An Autonomic Control Plane (ACP) Futurewei Technologies Inc. USA
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Arbor Networks
Operations and Management ANIMA WG Autonomic functions need a control plane to communicate, which depends on some addressing and routing. This Autonomic Management and Control Plane should ideally be self-managing, and as independent as possible of configuration. This document defines such a plane and calls it the "Autonomic Control Plane", with the primary use as a control plane for autonomic functions. It also serves as a "virtual out-of-band channel" for Operations Administration and Management (OAM) communications over a network that provides automatically configured hop-by-hop authenticated and encrypted communications via automatically configured IPv6 even when the network is not configured, or misconfigured.
Autonomic Networking is a concept of self-management: Autonomic functions self-configure, and negotiate parameters and settings across the network. defines the fundamental ideas and design goals of Autonomic Networking. A gap analysis of Autonomic Networking is given in . The reference architecture for Autonomic Networking in the IETF is specified in the document . Autonomic functions need an autonomically built communications infrastructure. This infrastructure needs to be secure, resilient and re-usable by all autonomic functions. Section 5 of introduces that infrastructure and calls it the Autonomic Control Plane (ACP). More descriptively it would be the "Autonomic communications infrastructure for Management and Control". For naming consistency with that prior document, this document continues to use the name ACP though. Today, the management and control plane of networks typically uses a routing and forwarding table which is dependent on correct configuration and routing. Misconfigurations or routing problems can disrupt management and control channels. Traditionally, an out-of-band network has been used to avoid or allow recovery from such problems, or personnel are sent on site to access devices through out-of-band management ports (also called craft ports, serial console, management ethernet port). However, both options are expensive. In increasingly automated networks either centralized management systems or distributed autonomic service agents in the network require a control plane which is independent of the configuration of the network they manage, to avoid impacting their own operations through the configuration actions they take. This document describes a modular design for a self-forming, self-managing and self-protecting Autonomic Control Plane (ACP), which is a virtual in-band network designed to be as independent as possible of configuration, addressing and routing problems. The details how this is achieved are described in . The ACP is designed to remain operational even in the presence of configuration errors, addressing or routing issues, or where policy could inadvertently affect connectivity of both data packets or control packets. This document uses the term "Data-Plane" to refer to anything in the network nodes that is not the ACP, and therefore considered to be dependent on (mis-)configuration. This Data-Plane includes both the traditional forwarding-plane, as well as any pre-existing control-plane, such as routing protocols that establish routing tables for the forwarding plane. The Autonomic Control Plane serves several purposes at the same time: Autonomic functions communicate over the ACP. The ACP therefore directly supports Autonomic Networking functions, as described in . For example, Generic Autonomic Signaling Protocol (GRASP - ) runs securely inside the ACP and depends on the ACP as its "security and transport substrate". A controller or network management system can use it to securely bootstrap network devices in remote locations, even if the (Data-Plane) network in between is not yet configured; no Data-Plane dependent bootstrap configuration is required. An example of such a secure bootstrap process is described in . An operator can use it to log into remote devices, even if the network is misconfigured or not configured. This document describes these purposes as use cases for the ACP in , it defines the requirements in . gives an overview how the ACP is constructed. The normative part of this document starts with , where the ACP is specified. defines normative how to support ACP on L2 switches. explains normative how non-ACP nodes and networks can be integrated. The remaining sections are non-normative: reviews benefits of the ACP (after all the details have been defined), provides operational recommendations, provides additional explanations and describes additional details or future standard or propriety extensions that were considered not to be appropriate for standardization in this document but were considered important to document. There are no dependencies against to build a complete working and interoperable ACP according to this document. The ACP provides secure IPv6 connectivity, therefore it can be used not only as the secure connectivity for self-management as required for the ACP in , but it can also be used as the secure connectivity for traditional (centralized) management. The ACP can be implemented and operated without any other components of autonomic networks, except for the GRASP protocol. ACP relies on per-link DULL GRASP (see ) to autodiscover ACP neighbors, and includes the ACP GRASP instance to provide service discovery for clients of the ACP (see ) including for its own maintenance of ACP certificates. The document "Using Autonomic Control Plane for Stable Connectivity of Network OAM" describes how the ACP alone can be used to provide secure and stable connectivity for autonomic and non-autonomic Operations Administration and Management (OAM) applications. That document also explains how existing management solutions can leverage the ACP in parallel with traditional management models, when to use the ACP and how to integrate with potentially IPv4 only OAM backends. Combining ACP with Bootstrapping Remote Secure Key Infrastructures (BRSKI), see ) results in the "Autonomic Network Infrastructure" as defined in , which provides autonomic connectivity (from ACP) with secure zero-touch (automated) bootstrap from BRSKI. The ANI itself does not constitute an Autonomic Network, but it allows the building of more or less autonomic networks on top of it - using either centralized, Software Defined Networking- (SDN-)style (see ) automation or distributed automation via Autonomic Service Agents (ASA) / Autonomic Functions (AF) - or a mixture of both. See for more information.
Please see the following Terminology section () for explanations of terms used in this section. The design of the ACP as defined in this document is considered to be applicable to all types of "professionally managed" networks: Service Provider, Local Area Network (LAN), Metro(politan networks), Wide Area Network (WAN), Enterprise Information Technology (IT) and ->"Operational Technology" (OT) networks. The ACP can operate equally on layer 3 equipment and on layer 2 equipment such as bridges (see ). The hop-by-hop authentication and confidentiality mechanism used by the ACP is defined to be negotiable, therefore it can be extended to environments with different protocol preferences. The minimum implementation requirements in this document attempt to achieve maximum interoperability by requiring support for multiple options depending on the type of device: IPsec, see , and datagram Transport Layer Security version 1.2 (DTLS), see ). The implementation footprint of the ACP consists of Public Key Infrastructure (PKI) code for the ACP certificate, the GRASP protocol, UDP, TCP and TLS (for security and reliability of GRASP), the ACP secure channel protocol used (such as IPsec or DTLS), and an instance of IPv6 packet forwarding and routing via the Routing Protocol for Low-power and Lossy Networks (RPL), see , that is separate from routing and forwarding for the Data-Plane (user traffic). The ACP uses only IPv6 to avoid complexity of dual-stack ACP operations (IPv6/IPv4). Nevertheless, it can without any changes be integrated into even otherwise IPv4-only network devices. The Data-Plane itself would not need to change, it could continue to be IPv4 only. For such IPv4 only devices, the IPv6 protocol itself would be additional implementation footprint only used for the ACP. The protocol choices of the ACP are primarily based on wide use and support in networks and devices, well understood security properties and required scalability. The ACP design is an attempt to produce the lowest risk combination of existing technologies and protocols to build a widely applicable operational network management solution: RPL was chosen because it requires a smaller routing table footprint in large networks compared to other routing protocols with an autonomically configured single area. The deployment experience of large scale Internet of Things (IoT) networks serves as the basis for wide deployment experience with RPL. The profile chosen for RPL in the ACP does not leverage any RPL specific forwarding plane features (IPv6 extension headers), making its implementation a pure control plane software requirement. GRASP is the only completely novel protocol used in the ACP, and this choice was necessary because there is no existing suitable protocol to provide the necessary functions to the ACP, so GRASP was developed to fill that gap. The ACP design can be applicable to (cpu, memory) constrained devices and (bitrate, reliability) constrained networks, but this document does not attempt to define the most constrained type of devices or networks to which the ACP is applicable. RPL and DTLS for ACP secure channels are two protocol choices already making ACP more applicable to constrained environments. Support for constrained devices in this specification is opportunistic, but not complete, because the reliable transport for GRASP (see ) only specifies TCP/TLS). See for discussions about how future standards or proprietary extensions/variations of the ACP could better meet different expectations from those on which the current design is based including supporting constrained devices better.
[RFC Editor: WG/IETF/IESG review of the terms below asked for references between these terms when they refer to each other. The only option I could fin RFC/XML to point to a hanging text acronym definition that also displays the actual term is the format="title" version, which leads to references such as '->"ACP domain certificate" ()'. I found no reasonable way to eliminate the trailing '()' generated by this type of cross references. Can you please take care of removing these artefacts during editing (after conversion to nroff ?). I also created a ticket to ask for an xml2rfc enhancement to avoid this in the future: [RFC Editor: Question: Is it possible to change the first occurrences of [RFCxxxx] references to "rfcxxx title" [RFCxxxx]? the XML2RFC format does not seem to offer such a format, but I did not want to duplicate 50 first references - one reference for title mentioning and one for RFC number.] In the rest of the document we will refer to systems using the ACP as "nodes". Typically such a node is a physical (network equipment) device, but it can equally be some virtualized system. Therefore, we do not refer to them as devices unless the context specifically calls for a physical system. This document introduces or uses the following terms (sorted alphabetically). Terms introduced are explained on first use, so this list is for reference only. "Autonomic Control Plane". The Autonomic Function as defined in this document. It provides secure zero-touch (automated) transitive (network wide) IPv6 connectivity for all nodes in the same ACP domain as well as a GRASP instance running across this ACP IPv6 connectivity. The ACP is primarily meant to be used as a component of the ANI to enable Autonomic Networks but it can equally be used in simple ANI networks (with no other Autonomic Functions) or completely by itself. An IPv6 address assigned to the ACP node. It is stored in the domain information field of the ->"ACP domain certificate". The ACP address may imply a range or set of addresses that the node can assign for different purposes. This address range/set is derived by the node from the format of the ACP address called the "addressing sub-scheme". An interface on an ACP node providing access to the ACP for non ACP capable nodes without using an ACP secure channel. See . The ACP domain is the set of nodes with ->"ACP domain certificates" that allow them to authenticate each other as members of the ACP domain. See also . A certificate (LDevID) carrying the domain information field which is used by the ACP to learn its address in the ACP and to derive and cryptographically assert its membership in the ACP domain. An rfc822Name information element (e.g., field) in the domain certificate in which the ACP relevant information is encoded: the domain name and the ACP address. The Loopback interface in the ACP Virtual Routing and Forwarding (VRF) that has the ACP address assigned to it. The ACP network constitutes all the nodes that have access to the ACP. It is the set of active and transitively connected nodes of an ACP domain plus all nodes that get access to the ACP of that domain via ACP edge nodes. The /48 IPv6 address prefixes used across the ACP. In the normal/simple case, the ACP has one ULA prefix, see . The ACP routing table may include multiple ULA prefixes if the "rsub" option is used to create addresses from more than one ULA prefix. See . The ACP may also include non-ULA prefixes if those are configured on ACP connect interfaces. See . A cryptographically authenticated and encrypted data connection established between (normally) adjacent ACP nodes to carry traffic of the ACP VRF securely and isolated from Data-Plane traffic in-band over the same link/path as the Data-Plane. The protocol used to build an ACP secure channel, e.g., Internet Key Exchange Protocol version 2 (IKEv2) with IPsec or Datagram Transport Layer Security (DTLS). An interface in the ACP VRF mapped to one or more ACP secure channels. See . "Autonomic Network": A network according to . Its main components are ANI, Autonomic Functions and Intent. An FQDN (Fully Qualified Domain Name) in the domain information field of the Domain Certificate. See . "Autonomic Network Infrastructure". The ANI is the infrastructure to enable Autonomic Networks. It includes ACP, BRSKI and GRASP. Every Autonomic Network includes the ANI, but not every ANI network needs to include autonomic functions beyond the ANI (nor Intent). An ANI network without further autonomic functions can for example support secure zero-touch (automated) bootstrap and stable connectivity for SDN networks - see . "Autonomic Networking Integrated Model and Approach". ACP, BRSKI and GRASP are products of the IETF ANIMA working group. "Autonomic Service Agent". Autonomic software modules running on an ANI device. The components making up the ANI (BRSKI, ACP, GRASP) are also described as ASAs. A function/service in an Autonomic Network (AN) composed of one or more ASA across one or more ANI nodes. "Bootstrapping Remote Secure Key Infrastructures" (. A protocol extending EST to enable secure zero-touch bootstrap in conjunction with ACP. ANI nodes use ACP, BRSKI and GRASP. The counterpoint to the ACP VRF in an ACP node: all routing and forwarding in the node other than the ACP VRF. In a simple ACP or ANI node, the Data-Plane is typically provisioned by means other than autonomically, for example manually (including across the ACP) or via SDN controllers. In a fully Autonomic Network node, the Data-Plane is managed autonomically via Autonomic Functions and Intent. Note that other (non-ANIMA) RFCs use the Data-Plane to refer to what is better called the forwarding plane. This is not the way the term is used in this document! A physical system, or physical node. The process where a node presents identification (for example through keying material such as the private key of an IDevID) to a network and acquires a network specific identity uch as an LDevID and trust anchors such as Certificate Authority (CA) certificates. "Enrollment over Secure Transport" (). IETF standard-track protocol for enrollment of a node with an LDevID. BRSKI is based on EST. "Generic Autonomic Signaling Protocol". An extensible signaling protocol required by the ACP for ACP neighbor discovery. The ACP also provides the "security and transport substrate" for the "ACP instance of GRASP". This instance of GRASP runs across the ACP secure channels to support BRSKI and other NOC/OAM or Autonomic Functions. See . An "Initial Device IDentity" X.509 certificate installed by the vendor on new equipment. Contains information that establishes the identity of the node in the context of its vendor/manufacturer such as device model/type and serial number. See . IDevID cannot be used for the ACP because they are not provisioned by the owner of the network, so they can not directly indicate an ACP domain they belong to. The type of management used predominantly in IP based networks, not leveraging an ->"out-of-band network". In in-band management, access to the managed equipment depends on the configuration of this equipment itself: interface, addressing, forwarding, routing, policy, security, management. This dependency makes in-band management fragile because the configuration actions performed may break in-band management connectivity. Breakage can not only be unintentional, it can simply be an unavoidable side effect of being unable to create configuration schemes where in-band management connectivity configuration is unaffected by Data-Plane configuration. See also ->"(virtual) out-of-band network". Policy language of an autonomic network according to . The conventional name for an internal IP interface to which addresses may be assigned, but which transmits no external traffic. A "Local Device IDentity" is an X.509 certificate installed during "enrollment". The Domain Certificate used by the ACP is an LDevID. See . "Manufacturer Installed Certificate". This is another word to describe an IDevID in referenced materials. This term is not used in this document. Interfaces existing on a node without configuration of the already running node. On physical nodes these are usually physical interfaces. On virtual nodes their equivalent. A system, e.g., supporting the ACP according to this document. Can be virtual or physical. Physical nodes are called devices. The identifier of an ACP node inside that ACP. It is the last 64 (see ) or 78-bits (see ) of the ACP address. "": "The hardware and software dedicated to detecting or causing changes in physical processes through direct monitoring and/or control of physical devices such as valves, pumps, etc.". OT networks are today in most cases well separated from Information Technology (IT) networks. An out-of-band network is a secondary network used to manage a primary network. The equipment of the primary network is connected to the out-of-band network via dedicated management ports on the primary network equipment. Serial (console) management ports were historically most common, higher end network equipment now also has ethernet ports dedicated only for management. An out-of-band network provides management access to the primary network independent of the configuration state of the primary network. One of the goals of the ACP is to provide this benefit of out-of-band networks virtually on the primary network equipment. The ACP VRF acts as a virtual out of band network device providing configuration independent management access. The ACP secure channels are the virtual links of the ACP virtual out-of-band network, meant to be operating independent of the configuration of the primary network. See also ->"in-band (management)". "IPv6 Routing Protocol for Low-Power and Lossy Networks". The routing protocol used in the ACP. See . "Manufacturer Authorized Signing Authority". A vendor/manufacturer or delegated cloud service on the Internet used as part of the BRSKI protocol. An ACP registrar is an entity (software and/or person) that is orchestrating the enrollment of ACP nodes with the ACP domain certificate. ANI nodes use BRSKI, so ANI registrars are also called BRSKI registrars. For non-ANI ACP nodes, the registrar mechanisms are undefined by this document. See . Renewal and other maintenance (such as revocation) of ACP domain certificates may be performed by other entities than registrars. EST must be supported for ACP domain certificate renewal (see ). BRSKI is an extension of EST, so ANI/BRSKI registrars can easily support ACP domain certificate renewal in addition to initial enrollment. "secured Unique Device Identifier". This is another word to describe an IDevID in referenced material. This term is not used in this document. "Unique Device Identifier". In the context of this document unsecured identity information of a node typically consisting of at least device model/type and serial number, often in a vendor specific format. See sUDI and LDevID. A "Unique Local Address" (ULA) is an IPv6 address in the block fc00::/7, defined in . It is the approximate IPv6 counterpart of the IPv4 private address (). The ULA Global ID prefix are the first 48-bits of a ULA address. In this document it is abbreviated as "ULA prefix". The ACP is modeled in this document as a "Virtual Routing and Forwarding" instance (VRF). This means that it is based on a "virtual router" consisting of a separate IPv6 forwarding table to which the ACP virtual interfaces are attached and an associated IPv6 routing table separate from the Data-Plane. Unlike the VRFs on MPLS/VPN-PE () or LISP XTR (), the ACP VRF does not have any special "core facing" functionality or routing/mapping protocols shared across multiple VRFs. In vendor products a VRF such as the ACP-VRF may also be referred to as a so called VRF-lite. An ACP zone is a set of ACP nodes using the same zone field value in their ACP address according to . Zones are a mechanism to support structured addressing of ACP addresses within the same /48-bit ULA prefix. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119],[RFC8174] when, and only when, they appear in all capitals, as shown here.
The following requirements were identified for the design of the ACP based on the above use-cases (). These requirements are informative. The ACP as specified in the normative parts of this document is meeting or exceeding these use-case requirements: The ACP should provide robust connectivity: As far as possible, it should be independent of configured addressing, configuration and routing. Requirements 2 and 3 build on this requirement, but also have value on their own. The ACP must have a separate address space from the Data-Plane. Reason: traceability, debug-ability, separation from Data-Plane, infrastructure security (filtering based on known address space). The ACP must use autonomically managed address space. Reason: easy bootstrap and setup ("autonomic"); robustness (admin cannot break network easily). This document suggests using ULA addressing for this purpose ("Unique Local Address", see ). The ACP must be generic, that is it must be usable by all the functions and protocols of the ANI. Clients of the ACP must not be tied to a particular application or transport protocol. The ACP must provide security: Messages coming through the ACP must be authenticated to be from a trusted node, and should (very strong should) be encrypted. Explanation for ACP4: In a fully autonomic network (AN), newly written ASA could potentially all communicate exclusively via GRASP with each other, and if that was assumed to be the only requirement against the ACP, it would not need to provide IPv6 layer connectivity between nodes, but only GRASP connectivity. Nevertheless, because ACP also intends to support non-AN networks, it is crucial to support IPv6 layer connectivity across the ACP to support any transport and application layer protocols. The ACP operates hop-by-hop, because this interaction can be built on IPv6 link local addressing, which is autonomic, and has no dependency on configuration (requirement 1). It may be necessary to have ACP connectivity across non-ACP nodes, for example to link ACP nodes over the general Internet. This is possible, but introduces a dependency against stable/resilient routing over the non-ACP hops (see ).
The Autonomic Control Plane is constructed in the following way (for details, see ): An ACP node creates a Virtual Routing and Forwarding (VRF) instance, or a similar virtual context. It determines, following a policy, a candidate peer list. This is the list of nodes to which it should establish an Autonomic Control Plane. Default policy is: To all link-layer adjacent nodes supporting ACP. For each node in the candidate peer list, it authenticates that node (according to ) and negotiates a mutually acceptable channel type. For each node in the candidate peer list, it then establishes a secure tunnel of the negotiated channel type. The resulting tunnels are then placed into the previously set up VRF. This creates an overlay network with hop-by-hop tunnels. Inside the ACP VRF, each node assigns its ULA IPv6 address to a Loopback interface assigned to the ACP VRF. Each node runs a lightweight routing protocol, to announce reachability of the virtual addresses inside the ACP (see ). Note: Non-ACP NMS ("Network Management Systems") or SDN controllers have to be explicitly configured for connection into the ACP. Connecting over non-ACP Layer-3 clouds requires explicit configuration. See . None of the above operations (except explicit configured ones) are reflected in the configuration of the node. The following figure illustrates the ACP.
This section describes the components and steps to set up an Autonomic Control Plane (ACP), and highlights the key properties which make it "indestructible" against many inadvertent changes to the Data-Plane, for example caused by misconfigurations. An ACP node can be a router, switch, controller, NMS host, or any other IP capable node. Initially, it must have its ACP domain certificate, as well as an (empty) ACP Adjacency Table (described in ). It then can start to discover ACP neighbors and build the ACP. This is described step by step in the following sections:
The ACP relies on group security. An ACP domain is a group of nodes that trust each other to participate in ACP operations such as creating ACP secure channels in an autonomous peer-to-peer fashion between ACP domain members via protocols such as IPsec. To establish trust, each ACP member requires keying material: An ACP node MUST have a certificate (LDevID) and a Trust Anchor (TA) consisting of a certificate (chain) used to sign the LDevID of all ACP domain members. The LDevID is used to cryptographically authenticate the membership of its owner node in the ACP domain to other ACP domain members. The TA is used to authenticate the ACP domain membership of other nodes (see ). Manual keying via shared secrets is not usable for an ACP domain because it would require a single shared secret across all current and future ACP domain members to meet the expectation of autonomous, peer-to-peer establishment of ACP secure channels between any ACP domain members. Such a single shared secret would be an inacceptable security weakness. Asymmetric keying material (public keys) without certificates does not provide the mechanisms to authenticate ACP domain membership in an autonomous, peer-to-peer fashion for current and future ACP domain members. The LDevID is called the ACP domain certificate, the TA is the Certificate Authority (CA) of the ACP domain. The ACP does not mandate specific mechanisms by which this keying material is provisioned into the ACP node. It only requires the certificate to comply with , specifically the Domain information field as specified in in its domain certificate as well as those of candidate ACP peers. See for more information about enrollment or provisioning options. This document uses the term ACP in many places where the Autonomic Networking reference documents and use the word autonomic. This is done because those reference documents consider (only) fully autonomic networks and nodes, but support of ACP does not require support for other components of autonomic networks except for relying on GRASP and providing security and transport for GRASP. Therefore the word autonomic might be misleading to operators interested in only the ACP. defines the term "Autonomic Domain" as a collection of autonomic nodes. ACP nodes do not need to be fully autonomic, but when they are, then the ACP domain is an autonomic domain. Likewise, defines the term "Domain Certificate" as the certificate used in an autonomic domain. The ACP domain certificate is that domain certificate when ACP nodes are (fully) autonomic nodes. Finally, this document uses the term ACP network to refer to the network created by active ACP nodes in an ACP domain. The ACP network itself can extend beyond ACP nodes through the mechanisms described in .
ACP domain certificates MUST be compliant X.509 certificates. ACP nodes MUST support RSA and Elliptic Curve (ECC) public keys in ACP certificates. ACP certificates wth ECC keys MUST indicate to be Elliptic Curve Diffie-Hellman capable (ECDH) if X.509 v3 keyUsage and extendedKeyUsage are included in the certificate. ACP nodes MUST support Certificates RSA keys with no less than 2048 bit key length and ECC keys with NIST P-256, P-384 and P-521 key length (and curve) or better. ACP nodes MUST support SHA-256, SHA-384, SHA-512 or better signatures for ACP certificates with RSA key and the same RSA signatures plus ECDSA signatures for ACP certificates with ECC key. The ACP certificate SHOULD use an RSA key and an RSA signature when the ACP certificate is intended to be used not only for ACP authentication but also for other purposes. The ACP certificate MAY use an ECC key and an ECDSA signature if the ACP certificate is only used for ACP and ANI authentication and authorization. Any secure channel protocols used for the ACP as specified in this document or extensions of this document MUST therefore support authentication (e.g.:signing) starting with these type of certificates. See for more information. The reason for these choices are as follows: As of 2020, RSA is still more widely used than ECC, therefore the MUST for RSA. ECC offers equivalent security at (logarithmically) shorter key lengths (see ). This can be beneficial especially in the presence of constrained bandwidth or constrained nodes in an ACP/ANI network. Some ACP functions such as GRASP peer-2-peer across the ACP require end-to-end/any-to-any authentication/authorization, therefore ECC can only reliably be used in the ACP when it MUST be supported on all ACP nodes. RSA signatures are mandatory to be supported also for ECC certificates because CAs themselves may not support ECC yet. For further certificate details, ACP certificates may follow the recommendations from . The ACP domain certificate SHOULD be used for any authentication between nodes with ACP domain certificates (ACP nodes and NOC nodes) where the required authorization condition is ACP domain membership, such as ACP node to NOC/OAM end-to-end security and ASA to ASA end-to-end security. defines this "ACP domain membership check". The uses of this check that are standardized in this document are for the establishment of hop-by-hop ACP secure channels () and for ACP GRASP () end-to-end via TLS (). The ACP domain membership check requires a minimum amount of elements in a certificate as described in . All elements are compliant. The identity of a node in the ACP is carried via the ACP Domain Information Field as defined in which is encoded as an rfc822Name field. Any other field of the ACP domain certificate is to be populated as required by or desired by the operator of the ACP domain ACP registrars/CA and required by other purposes that the ACP domain certificate is intended to be used for. For diagnostic and other operational purposes, it is beneficial to copy the device identifying fields of the node's IDevID into the ACP domain certificate, such as the "serialNumber" (see section 2.3.1). Inclusion of this information makes it easier to potentially attack the node though, for example by learning the device model, which may help to select a fitting subset of attacks. Neighboring attackers can retrieve the certificate through an otherwise unsuccessful initiation of a secure channel association. Note that there is no intention to constrain authorization within the ACP or autonomic networks using the ACP to just the ACP domain membership check as defined in this document. It can be extended or modified with future requirements. Such future authorizations can use and require additional elements in certificates or policies or even additional certificates. For an example, see .
Information about the domain MUST be encoded in the domain certificate in a subjectAltName / rfc822Name field according to the following ABNF () definition: [RFC Editor: Please substitute SELF in all occurrences of rfcSELF in this document with the RFC number assigned to this document and remove this comment line]
] ; as of RFC1034, section 3.5 acp-domain-name = ; ; as of RFC 1034, section 3.5 extensions = *( "+" extension ) extension = ; future standard definition. ; Must fit RFC5322 simple dot-atom format. routing-subdomain = [ rsub " ." ] acp-domain-name Example: given an ACP address of fd89:b714:f3db:0:200:0:6400:0000 and an ACP domain-name of and an rsub extenstion of area51.research then this results in: domain-information = rfcSELF+FD89B714F3DB00000200000064000000 acp-domain-name = routing-subdomain = ]]>
domain-information is the encoded information that is put into the ACP domain certificates subjectAltName / rfc822Name field. routing-subdomain is a string that can be constructed from the domain-information, and it is used in the hash-creation of the ULA (see below). The requirements and sementics of the parts of this information are explained in the following paragraphs: Nodes complying with this specification MUST be able to receive their ACP address through the domain certificate, in which case their own ACP domain certificate MUST have the 32HEXDIG "acp-address" field. Nodes complying with this specification MUST also be able to authenticate nodes as ACP domain members or ACP secure channel peers when they have a 0-value acp-address field and as ACP domain members (but not as ACP secure channel peers) when they have an empty acp-address field. See . "acp-domain-name" is used to indicate the ACP Domain across which all ACP nodes trust each other and are willing to build ACP channels to each other. See . Acp-domain-name SHOULD be the FQDN of a DNS domain owned by the operator assigning the certificate. This is a simple method to ensure that the domain is globally unique and collision of ACP addresses would therefore only happen due to ULA hash collisions (see ). If the operator does not own any FQDN, it should choose a string (in FQDN format) that it intends to be equally unique. To keep the encoding simple, there is no consideration for internationalized acp-domain-names. The ACP domain information is not intended for enduser consumption, and there is no protection against someone not owning a domain name to simpy choose it. Instead, it only serves as a hash seed for the ULA and for diagnostics to the operator. Therefore, any operator owning only an internationalized domain name should be able to pick an equivalently unique 7-bit ASCII acp-domain-name string representing the internationalized domain name. "routing-subdomain" is a heuristic that allows a Registrar to consistently generate a unique 48-bit ULA prefix for ACP addresses. The presence of the "rsub" component allows to a single ACP domain to employ multiple /48 ULA prefixes. See for example use-cases. The optional "extensions" field is used for future standardized extensions to this specification. It MUST be ignored if present and not understood. Formatting notes: "rsub" needs to be in the "local-part": If the format just had routing-subdomain as the domain part of the domain-information, rsub and acp-domain-name could not be separated from each other. It also makes domain-information a valid e-mail target across all routing-subdomains. "acp-address" cannot use standard IPv6 address formats because it must match the simple dot-atom format of . The character ":" is not allowed in that format. If "acp-address" is empty, and "rsub" is empty too, the "local-part" will have the format "rfcSELF++extension(s)". The two plus characters are necessary so the node can unambiguously parse that both "acp-address" and "rsub" are empty. The maximum size of "domain-information" is 254 characters and the maximum size of local-part is 64 characters according to that is referring to (superseded by ). The subjectAltName / rfc822Name encoding of the ACP domain name and ACP address is used for the following reasons: Rfc822name encoding for the ACP domain information was choosen for the following reasons. The ACP domain information field is the identifier of a node's ACP. It includes the the necessary components to identify a nodes ACP both from within the ACP as well as from the outside of the ACP. For manual and/or automated diagnostics and backend management of devices and ACPs, it is necessary to have an easily human readible and software parsed standard, single string representation of the ACP domain information. For example, inventory or other backend systems can always identify an entity by one unique string field but not by a combination of multiple fields, which would be necessary if there was no single string representation. If the encoding of the ACP domain information into the ACP domains certificate was not that of such a string, it would be necessary to define a second standard encoding to provide this format (standard string encoding). Rfc822 addresses have become standard identifiers of entities in many systems, including the majority of user identification in web or mobile applications, where in many cases, e-mail is not even part of the service for which an rfc822 address is used as an entities identifier. In single-sign-on systems for example, <local-part>@<domain> is instead used to indicate a <domain> with which authentication and authorization of <local-part> is performend without any other use of RFC822 than its address format (e.g.: no rfc822 formatted message exchanges). Encoding the ACP nodes identity/name in the format of an rfc822address is therefore following common practices for how rfc822 addresses are used in other contexts. It also very well matches the format of rfc822 address structure <local-part>@<domain> because the ACP domain information does logically also consist of a <domain> identifying the ACP, and a <local-part> identifying a nodes ACP. subjectAltName / rfc822Name is the standard, mandatory to implement certificate attribute to encode the certificate subjects rfc822 address and can be the only subjects name. Compatibilities: It should be possible to use the ACP domain certificate as an LDevID on the system for other uses beside the ACP. Therefore, the information element required for the ACP should be encoded so that it minimizes the possibility of creating incompatibilities with such other uses. The subjectName for example is for example often used as an entity identifier in non-ACP uses. The element should not require additional ASN.1 en/decoding, because libraries to access certificate information especially for embedded devices may not support extended ASN.1 decoding beyond predefined, manadatory fields. subjectAltName / rfc822Name is such a mandatory predefined field. subjectAlName / otherName for example is not. Encoding of the ACP domain information as a human readable string in a manadatory certificate field also has the benefit that it can be diagnosed/decoded in any pre-existing certificate diagnostic software. The element required for the ACP should not be misinterpreted by any other uses of the LDevID. If the element used for the ACP is interpreted by other components than the ACP, the impact should be benign. By using fully rfc822address compliant encoding, the benign side effect of non-ACP software using the ACP rfc822address would be emails sent to the mailbox identified by the rfc822address. If it is desired to receive such emails, suitable email software may also support assigning all rfc822addresses for an ACP domain to a single mailbox rfcSELF@<domain>. This is possible when "+" (which follows rfcSELF) is supported by the Mail User Agent as a separator between mail subscriber and sub-mailbox. See section of for details on the subjectAltName field.
The following points constitute the ACP domain membership check of a candidate peer via its certificate: The peer certificate is valid (lifetime). The peer has proved ownership of the private key associated with the certificate's public key. This check is performed by the security association protocol used, for example , section 2.15. The peer's certificate passes certificate path validation as defined in , section 6 against one of the Trust Anchors associated with the ACP node's ACP domain certificate (see below). If the node certificate indicates a Certificate Revocation List (CRL) Distribution Point (CDP) (, section or Online Certificate Status Protocol (OCSP) responder (, section, then the peer's certificate must be valid according to those criteria: An OCSP check for the peer's certificate across the ACP must succeed or the peer certificate must not be listed in the CRL retrieved from the CDP. This rule has to be skipped for ACP secure channel peer authentication when the node has no ACP or non-ACP connectivity to retrieve current CRL or access an OCSP responder (and the security association protocol itself has also no way to communicate CRL or OCSP check). The peer's certificate has a syntactically valid ACP domain information field (encoded as subjectAltName / rfc822Name) and the acp-domain-name in that peer's domain information field is the same as in this ACP node's certificate (lowercase normalized). Note: When an ACP node learns later via OCSP/CRL that an ACP peer's certificate for which rule 4 had to be skipped during ACP secure channel establishment is invalid, then the ACP secure channel to that peer SHOULD be closed even if this peer is the only connectivity to access CRL/OCSP. The ACP secure channel connection MUST be retried periodically to support the case that the neighbor aquires a new, valid certificate. When checking a candidate peer's certificate for the purpose of establishing an ACP secure channel, one additional check is performed: The candidate peer certificate's ACP domain information field has a non-empty acp-address field (either 32HEXDIG or 0, according to ). Technically, ACP secure channels can only be built with nodes that have an acp-address. Rule 6 ensures that this is taken into account during ACP domain membership check. Nodes with an empty acp-address field can only use their ACP domain certificate for non-ACP-secure channel authentication purposes. This includes for example NMS type nodes permitted to communicate into the ACP via ACP connect The special value 0 in an ACP certificates acp-address field is used for nodes that can and should determine their ACP address through other mechanisms than learning it through the acp-address field in their ACP domain certificate. These ACP nodes are permitted to establish ACP secure channels. Mechanisms for those nodes to determine their ACP address are outside the scope of this specification, but this option is defined here so that any ACP nodes can build ACP secure channels to them according to Rule 6. In summary: Steps 1...4 constitute standard certificate validity verification and private key authentication as defined by and security association protocols (such as IKEv2 when leveraging certificates. Steps 1...4 do not include verification of any pre-existing form of non-public-key-only based identity elements of a certificate such as a web servers domain name prefix often encoded in certificate common name. Steps 5 and 6 are the equivalent steps. Step 4 Constitutes standard CRL/OCSP checks refined for the case of missing connectivity and limited functionality security association protocols. Step 5 Checks for the presence of an ACP identity for the peer. Steps 1...5 authorize to build any secure connection between members of the same ACP domain except for ACP secure channels. Step 6 is the additional verification of the presence of an ACP address. Steps 1...6 authorize to build an ACP secure channel. For brevity, the remainder of this document refers to this process only as authentication instead of as authentication and authorization.
ACP nodes need Trust Point (TP) certificates to perform certificate path validation as required by , rule 3. Trust Point(s) must be provisioned to an ACP node (together with its ACP domain certificate) by an ACP Registrar during initial enrolment of a candidate ACP node. ACP nodes MUST also support renewal of TPs via EST as described below in . Trust Point is the term used in this document for a certificate authority (CA) and its associated set of certificates. Multiple certificates are required for a CA to deal with CA certificate renewals as explained in Section 4.4 of CMP (). A certificate path is a chain of certificates starting at the ACP certificate (leaf/end-entity) followed by zero or more intermediate Trust Point or sub-CA certificates and ending with a self-signed certificate of a so called root-CA or Trust Anchor. Certificate path validation authenticates that the ACP certificate is signed by a Trust Anchor, directly or indirectly via one or more intermediate Trust Points. Note that different ACP nodes may have different Trust Points and even different Trust Anchors in their certificate path, as long as the set of Trust Points for all ACP node includes the same set of Trust Anchors (usually 1), and each ACP nodes set of Trust Anchors includes the intermediate Trust Points for its own ACP domain certificate. The protocols through which ACP domain membership check rules 1-4 are performed therefore need to support the exchange not only of the ACP nodes certificates, but also their intermediate Trust Points. ACP nodes MUST support for the ACP domain membership check the certificate path validation with 0 or 1 intermediate Trust Points. They SHOULD support 2 intermediate Trust Points and two Trust Anchors (to permit migration to different root-CAs). Trust Points for ACP domain certificates must be trusted to sign certificates with valid ACP domain information fields only for trusted ACP registrars of that domain. This can be achieved by using Trust Anchors private to the owner of the ACP domain or potentially through appropriate contractual agreements between the involved parties. Public CA without such obligations and guarantees can not be used. A single owner can operate multiple independent ACP domains from the same set of private trust anchors (CAs) when the ACP Registrars are trusted not to permit certificates with incorrect ACP information fields to be signed, such as ACP information with a wrong acp-domain field. In this case, CAs can be completely unaware of ACP specifics, so that it should be possible to use any existing CA software. When ACP Registrars are not to be trusted, the correctness of the ACP domain information field for the candidate ACP node has to be verified by the CA signing the ACP domain certificate.
ACP nodes MUST support renewal of their Certificate and Trust Points (TP) via EST ("Enrollment over Secure Transport", see ) and MAY support other mechanisms. An ACP network MUST have at least one ACP node supporting EST server functionality across the ACP so that EST renewal is useable. ACP nodes SHOULD be able to remember the EST server from which they last renewed their ACP domain certificate and SHOULD provide the ability for this remembered EST server to also be set by the ACP Registrar (see ) that initially enrolled the ACP device with its ACP domain certificate. When BRSKI (see ) is used, the ACP address of the BRSKI registrar from the BRSKI TLS connection SHOULD be remembered and used for the next renewal via EST if that registrar also announces itself as an EST server via GRASP (see next section) on its ACP address. The EST server MUST present a certificate that is passing ACP domain membership check in its TLS connection setup (, rules 1..5, not rule 6 as this is not for an ACP secure channel setup). The EST server certificate MUST also contain the id-kp-cmcRA extended key usage extension and the EST client must check its presence. The additional check against the id-kp-cmcRA extended key usage extension field ensures that clients do not fall prey to an illicit EST server. While such illicit EST servers should not be able to support certificate signing requests (as they are not able to elicit a signing response from a valid CA), such an illicit EST server would be able to provide faked CA certificates to EST clients that need to renew their CA certificates when they expire. Note that EST servers supporting multiple ACP domains will need to have for each of these ACP domains a separate certificate and respond on a different transport address (IPv6 address and/or TCP port), but this is easily automated on the EST server as long as the CA does not restrict registrars to request certificates with the id-kp-cmcRA extended usage extension for themselves.
The ACP node SHOULD support Certificate Revocation Lists (CRL) via HTTP from one or more CRL Distribution Points (CDPs). The CDP(s) MUST be indicated in the Domain Certificate when used. If the CDP URL uses an IPv6 address (ULA address when using the addressing rules specified in this document), the ACP node will connect to the CDP via the ACP. If the CDP uses a domain name, the ACP node will connect to the CDP via the Data-Plane. It is common to use domain names for CDP(s), but there is no requirement for the ACP to support DNS. Any DNS lookup in the Data-Plane is not only a possible security issue, but it would also not indicate whether the resolved address is meant to be reachable across the ACP. Therefore, the use of an IPv6 address versus the use of a DNS name doubles as an indicator whether or not to reach the CDP via the ACP. A CDP can be reachable across the ACP either by running it on a node with ACP or by connecting its node via an ACP connect interface (see ). The CDP SHOULD use an ACP domain certificate for its HTTPs connections. The connecting ACP node SHOULD verify that the CDP certificate used during the HTTPs connection has the same ACP address as indicated in the CDP URL of the node's ACP domain certificate if the CDP URL uses an IPv6 address.
An ACP node may determine that its ACP domain certificate has expired, for example because the ACP node was powered down or disconnected longer than its certificate lifetime. In this case, the ACP node SHOULD convert to a role of a re-enrolling candidate ACP node. In this role, the node does maintain the trust anchor and certificate chain associated with its ACP domain certificate exclusively for the purpose of re-enrollment, and attempts (or waits) to get re-enrolled with a new ACP certificate. The details depend on the mechanisms/protocols used by the ACP registrars. Please refer to and for explanations about ACP registrars and vouchers as used in the following text. When ACP is intended to be used without BRSKI, the details about BRSKI and vouchers in the following text can be skipped. When BRSKI is used (i.e.: on ACP nodes that are ANI nodes), the re-enrolling candidate ACP node would attempt to enroll like a candidate ACP node (BRSKI pledge), but instead of using the ACP nodes IDevID, it SHOULD first attempt to use its ACP domain certificate in the BRSKI TLS authentication. The BRSKI registrar MAY honor this certificate beyond its expiration date purely for the purpose of re-enrollment. Using the ACP node's domain certificate allows the BRSKI registrar to learn that node's ACP domain information field, so that the BRSKI registrar can re-assign the same ACP address information to the ACP node in the new ACP domain certificate. If the BRSKI registrar denies the use of the old ACP domain certificate, the re-enrolling candidate ACP node MUST re-attempt re-enrollment using its IDevID as defined in BRSKI during the TLS connection setup. Both when the BRSKI connection is attempted with the old ACP domain certificate or the IDevID, the re-enrolling candidate ACP node SHOULD authenticate the BRSKI registrar during TLS connection setup based on its existing trust anchor/certificate chain information associated with its old ACP certificate. The re-enrolling candidate ACP node SHOULD only fall back to requesting a voucher from the BRSKI registrar when this authentication fails during TLS connection setup. When other mechanisms than BRSKI are used for ACP domain certificate enrollment, the principles of the re-enrolling candidate ACP node are the same. The re-enrolling candidate ACP node attempts to authenticate any ACP registrar peers during re-enrollment protocol/mechanisms via its existing certificate chain/trust anchor and provides its existing ACP domain certificate and other identification (such as the IDevID) as necessary to the registrar. Maintaining existing trust anchor information is especially important when enrollment mechanisms are used that unlike BRSKI do not leverage a voucher mechanism to authenticate the ACP registrar and where therefore the injection of certificate failures could otherwise make the ACP node easily attackable remotely. When using BRSKI or other protocol/mechanisms supporting vouchers, maintaining existing trust anchor information allows for re-enrollment of expired ACP certificates to be more lightweight, especially in environments where repeated acquisition of vouchers during the lifetime of ACP nodes may be operationally expensive or otherwise undesirable.
The formal CDDL definition is:
The objective-flags field is set to indicate synchronization. The loop-count is fixed at 1 since this is a link-local operation. In the above example the RECOMMENDED period of sending of the objective is 60 seconds. The indicated ttl of 210000 msec means that the objective would be cached by ACP nodes even when two out of three messages are dropped in transit. The session-id is a random number used for loop prevention (distinguishing a message from a prior instance of the same message). In DULL this field is irrelevant but must still be set according to the GRASP specification. The originator MUST be the IPv6 link local address of the originating ACP node on the sending interface. The 'objective-value' parameter is a string indicating the protocol available at the specified or implied locator. It must be a protocol supported by the node to negotiate a secure channel. IKEv2 as shown above is the protocol used to negotiate an IPsec secure channel. The locator-option is optional and only required when the secure channel protocol is not offered at a well-defined port number, or if there is no well-defined port number. "IKEv2" is the abbreviation for "Internet Key Exchange protocol version 2". It is the main protocol used by the Internet IP security architecture (IPsec). We therefore use the term "IKEv2" and not "IPsec" in the GRASP definitions and example above. "IKEv2" has a well-defined port number 500, but in the above example, the candidate ACP neighbor is offering ACP secure channel negotiation via IKEv2 on port 15000 (for the sake of creating a non-standard example). "DTLS" indicates datagram Transport Layer Security version 1.2. There is no default UDP port, it must always be locally assigned by the node. See . If a locator is included, it MUST be an O_IPv6_LOCATOR, and the IPv6 address MUST be the same as the initiator address (these are DULL requirements to minimize third party DoS attacks). The secure channel methods defined in this document use the objective-values of "IKEv2" and "DTLS". There is no distinction between IKEv2 native and GRE-IKEv2 because this is purely negotiated via IKEv2. A node that supports more than one secure channel protocol method needs to flood multiple versions of the "AN_ACP" objective so that each method can be accompanied by its own locator-option. This can use a single GRASP M_FLOOD message as shown in . Note that a node serving both as an ACP node and BRSKI Join Proxy may choose to distribute the "AN_ACP" objective and the respective BRSKI in the same M_FLOOD message, since GRASP allows multiple objectives in one message. This may be impractical though if ACP and BRSKI operations are implemented via separate software modules / ASAs. The result of the discovery is the IPv6 link-local address of the neighbor as well as its supported secure channel protocols (and non-standard port they are running on). It is stored in the ACP Adjacency Table (see ), which then drives the further building of the ACP to that neighbor. Note that the DULL GRASP objective described does intentionally not include ACP nodes ACP domain certificate even though this would be useful for diagnostics and to simplify the security exchange in ACP secure channel security association protocols (see ). The reason is that DULL GRASP messages are periodically multicasted across IPv6 subnets and full certificates could easily lead to fragmented IPv6 DULL GRASP multicast packets due to the size of a certificate. This would be highly undesirable.
To avoid attacks, initial discovery of candidate ACP peers cannot include any non-protected negotiation. To avoid re-inventing and validating security association mechanisms, the next step after discovering the address of a candidate neighbor can only be to try first to establish a security association with that neighbor using a well-known security association method. From the use-cases it seems clear that not all type of ACP nodes can or need to connect directly to each other or are able to support or prefer all possible mechanisms. For example, code space limited IoT devices may only support DTLS because that code exists already on them for end-to-end security, but low-end in-ceiling L2 switches may only want to support Media Access Control Security (MacSec, see 802.1AE () because that is also supported in their chips. Only a flexible gateway device may need to support both of these mechanisms and potentially more. Note that MacSec is not required by any profiles of the ACP in this specification but just mentioned as a likely next interesting secure channel protocol. To support extensible secure channel protocol selection without a single common MTI protocol, ACP nodes must try all the ACP secure channel protocols it supports and that are feasible because the candidate ACP neighbor also announced them via its AN_ACP GRASP parameters (these are called the "feasible" ACP secure channel protocols). To ensure that the selection of the secure channel protocols always succeeds in a predictable fashion without blocking, the following rules apply: An ACP node may choose to attempt to initiate the different feasible ACP secure channel protocols it supports according to its local policies sequentially or in parallel, but it MUST support acting as a responder to all of them in parallel. Once the first secure channel protocol succeeds, the two peers know each other's certificates because they must be used by all secure channel protocols for mutual authentication. The node with the lower Node-ID in the ACP address of its ACP domain certificate becomes Bob, the one with the higher Node-ID in the certificate Alice. A peer with an empty ACP address field in its ACP domain certificate becomes Bob (this specification does not define such peers, only the interoperability with them). Bob becomes passive, he does not attempt to further initiate ACP secure channel protocols with Alice and does not consider it to be an error when Alice closes secure channels. Alice becomes the active party, continues to attempt setting up secure channel protocols with Bob until she arrives at the best one from her view that also works with Bob. For example, originally Bob could have been the initiator of one ACP secure channel protocol that Bob prefers and the security association succeeded. The roles of Bob and Alice are then assigned and the connection setup is completed. The protocol could for example be IPsec via IKEv2 ("IP security", see and "Internet Key Exchange protocol version 2", see . It is now up to Alice to decide how to proceed. Even if the IPsec connection from Bob succeeded, Alice might prefer another secure protocol over IPsec (e.g., FOOBAR), and try to set that up with Bob. If that preference of Alice succeeds, she would close the IPsec connection. If no better protocol attempt succeeds, she would keep the IPsec connection. The following sequence of steps show this example in more detail:
[1] Node 1 sends GRASP AN_ACP message to announce itself [2] Node 2 sends GRASP AN_ACP message to announce itself [3] Node 2 receives [1] from Node 1 [4:C1] Because of [3], Node 2 starts as initiator on its preferred secure channel protocol towards Node 1. Connection C1. [5] Node 1 receives [2] from Node 2 [6:C2] Because of [5], Node 1 starts as initiator on its preferred secure channel protocol towards Node 2. Connection C2. [7:C1] Node1 and Node2 have authenticated each others certificate on connection C1 as valid ACP peers. [8:C1] Node 1 certificate has lower ACP Node-ID than Node2, therefore Node 1 considers itself Bob and Node 2 Alice on connection C1. Connection setup C1 is completed. [9] Node 1 (Bob)) refrains from attempting any further secure channel connections to Node 2 (Alice) as learned from [2] because it knows from [8:C1] that it is Bob relative to Node 1. [10:C2] Node1 and Node2 have authenticated each others certificate on connection C2 (like [7:C1]). [11:C2] Node 1 certificate has lower ACP Node-ID than Node2, therefore Node 1 considers itself Bob and Node 2 Alice on connection C1, but they also identify that C2 is to the same mutual peer as their C1, so this has no further impact. [12:C2] Node 1 (Alice) closes C1. Because of [8:C1], Node 2 (Bob) expected this. [13] Node 1 (Alice) and Node 2 (Bob) start data transfer across C2, which makes it become a secure channel for the ACP.
Due to Channel Selection, ACP can support an evolving set of security association protocols. These protocols only need to be used to establish secure channels with L2 adjacent ACP neighbors and only optionally (where needed) across non-ACP capable L3 network (see ). Therefore, there is architecturally no need for any network wide mandatory to implement (MTI) security association protocols. Instead, ACP nodes only need to implement those protocols required to be supported by their neighbors. See for an example of this. The authentication of peers in any security association protocol MUST use the ACP domain certificate according to . Because auto-discovery of candidate ACP neighbors via GRASP (see ) as specified in this document does not communicate the neighbors ACP domain certificate, and ACP nodes may not (yet) have any other network connectivity to retrieve certificates, any security association protocol MUST use a mechanism to communicate the certificate directly instead of relying on a referential mechanism such as communicating only a hash and/or URL for the certificate. Any security association protocol MUST provide Forward Secrecy (whether inherently or as part of a profile of the security association protocol). The degree of security required on every hop of an ACP network needs to be consistent across the network so that there is no designated "weakest link" because it is that "weakest link" that would otherwise become the designated point of attack. When the secure channel protection on one link is compromised, it can be used to send/receive packets across the whole ACP network. This principle does not imply that the requirements against ACP security association protocols have to be the same across all subnets in an ACP network: Underlying L2 mechanisms such as strong encrypted radio technologies or may offer equivalent encryption and the ACP security association protocol may only be required to authenticate ACP domain membership of a peer and/or derive a key for the L2 mechanism. Mechanisms to auto-discover and associate ACP peers leveraging such underlying L2 security are possible and desirable to avoid duplication of encryption, but none are specified in this document. Strong physical security of a link may stand in where cryptographic security is infeasible. As there is no secure mechanism to automatically discover strong physical security solely between two peers, it can only be used with explicit configuration and that configuration too could become an attack vector. This document therefore only specifies with ACP connect one explicitly configured mechanism without any secure channel association protocol - for the case where both the link and the nodes attached to it have strong physical security. The following sub-sections define the security association protocols that are considered to be important and feasible to specify in this document.
An ACP node announces its ability to support IPsec, negotiated via IKEv2, as the ACP secure channel protocol using the "IKEv2" objective-value in the "AN_ACP" GRASP objective. The ACP usage of IPsec and IKEv2 mandates a narrow profile of the current standards-track usage guidance for IPsec and IKEv2 . This profile provides for stringent security properties and can exclude deprecated/legacy algorithms because there is no need for interoperability with legacy equipment for ACP secure channels. Any such backward compatibility would lead only to increased attack surface and implementation complexity, for no benefit.
ACP IPsec implementations MUST comply with (and its updates), with the following modifications to simplify hardware accelerated ACP IPsec implementation requirements by eliminating requirements for legacy or cryptographically weak options. ACP MUST NOT use any NULL encryption option due to the confidentiality of ACP payload that may not be encrypted by itself when carrying legacy management protocol traffics as well as hop-by-hop GRASP, which is designed to rely on the ACP for confidentiality of hop-by-hop distributed information. Therefore, IPsec MUST support ESP and MUST NOT use AH. For ESP, ENCR_NULL MUST NOT be used for ACP secure channels. Only ENCR_AES_GCM_16 is REQUIRED as an encryption algorithm for ACP secure channels with ESP. If an ACP node can perform ENCR_AES_CBC, ENCR_AES_CCM_8 at higher performance than ENCR_AES_GCM_16 or ENCR_CHACHA20_POLY1305 at equal or higher performance than ENCR_AES_GCM_16 then that ACP node SHOULD support such an encryption algorithm and prefer it in the IKEv2 negotiation if its performance is higher than that of ENCR_AES_GCM_16. Otherwise there are no normative requirements against either of these options. These requirements are overriding the MUST/SHOULD/SHOULD requirements of for these three algorithms for the following reasons: There is no unconditional requirement against ENCR_AES_CBC because ENCR_AES_GCM_16 is assumed to be feasible with less cost/higher higher performance in modern devices hardware accelerated implementations compared to ENCR-AES_CBC. AES-GCM is an authenticated encryption with associated data (AEAD) cipher mode, so no ESP authentication algorithm requirement is needed (unless further encryption algorithms are supported), further simplifying ACP IPsec implementations. there is no requirement to interoperate with legacy equipment in ACP secure channels, so a single MTI encryption algorithm for IPsec in ACP secure channels is sufficient for interoperability. There is no unconditional requirement against ENCR_AES_CCM_8 because it is currently not likely that it would be preferrable in ACP secure channels for more constrained IoT devices over options such as DTLS. In this algorithm is more desirable, because of solutions relying only on IPsec without such non-IPsec alternatives. There is no unconditional requirement against ENCR_CHACHA20_POLY1305 because there is currently no mechanism in the ACP to migrate all secure channels in an ACP domain to a different preferred encryption algorithm in the case of future discovered crypto weaknesses of AES. Once such mechanisms are defined, ENCR_CHACHA20_POLY1305 would be a good encryption algorithm, but due to the transitive traffic through ACP secure channels only when this does not result in an unexpected drop in performance. When using AES for encryption, keys less than 256 bits MUST NOT be used, and 256-bit keys MUST be supported. Once there are updates to , these should accordingly be reflected in updates to these ACP requirements, for example if ENCR_AES_GCM_16 was to be superceeded in the future.
IKEv2 for ACP secure channels MUST support the requirements of (as necessary to support the above described modified requirements for IPsec via ESP). Because IKEv2 for ACP secure channels is sufficient to be implemented in control plane software as opposed to ESP (which may need to be implemented in accelerated forwarding plane for sufficient performance), there are no restrictions on the requirements of for ACP secure channels. Instead, the following paragraphs describe additional or stricter requirements necessary for the authentication of ACP secure channels in IKEv2 via ACP domain certificates. IKEv2 Diffie-Hellman key exchange group 19 (256-bit random ECP) MUST be supported (in addition to 2048-bit MODP). ECC provides a similar security level to finite-field (MODP) key exchange with a shorter key length, so is generally preferred absent other considerations. IKEv2 authentication MUST use the ACP domain certificates. The Certificate Encoding "PKCS #7 wrapped X.509 certificate" (1) MUST be supported (see for this and other IANA IKEv2 parameter names used in this text). If certificate chains are used, all intermediate certificates up to, but not including the locally provisioned trust anchor certificate must be signaled. A certificate payload with the ACP certificate MUST be included during IKEv2 authentication to support the ACP domain membership check as described in , because it is using additional elements of the ACP certificates. ACP peers are expected to have the same set of Trust Anchors (TA), so a certificate path MUST only be included in the signaled payload when the path contains intermediate certificates not in the TA set, such as sub-CAs (see ). In IKEv2, ACP nodes are identified by their ACP address. The ID_IPv6_ADDR IKEv2 identification payload MUST be used and MUST convey the ACP address. If the peer's ACP domain certificate includes an ACP address in the ACP domain information field (not "0" or empty), the address in the IKEv2 identification payload must match it. See for more information about "0" or empty ACP address fields in the ACP domain information field. IKEv2 authentication MUST use authentication method 14 ("Digital Signature") for ACP certificates; this authentication method can be used with both RSA and ECDSA certificates, as indicated by a PKIX-style OID. The Digital Signature hash SHA2-512 MUST be supported (in addition to SHA2-256).
In network devices it is often more common to implement high performance virtual interfaces on top of GRE encapsulation than on top of a "native" IPsec association (without any other encapsulation than those defined by IPsec). On those devices it may be beneficial to run the ACP secure channel on top of GRE protected by the IPsec association. To run ACP via GRE/IPsec, no further IANA assignments/definitions are required. The requirements for ESP/IPsec/IKEv2 are the same as for native IPsec (see ) except that IPsec transport mode and next protocol GRE (47) are to be negotiated. Tunnel mode is not required because of GRE. If IKEv2 initiator and responder support IPsec over GRE, it has to be preferred over native IPsec. The ACP IPv6 traffic has to be carried across GRE according to .
We define the use of ACP via DTLS in the assumption that it is likely the first transport encryption supported in some classes of constrained devices. An ACP node announces its ability to support DTLS (as described here) as an ACP secure channel protocol in GRASP through the "DTLS" objective-value in the "AN_ACP" objective. To run ACP via UDP and DTLS v1.2 a locally assigned UDP port is used that is announced as a parameter in the GRASP AN_ACP objective to candidate neighbors. All ACP nodes supporting DTLS as a secure channel protocol MUST adhere to the DTLS implementation recommendations and security considerations of BCP 195 except with respect to the DTLS version. ACP nodes supporting DTLS MUST implement only DTLS 1.2 or later. For example, implementing DTLS-1.3 () is also an option. There is no additional session setup or other security association besides this simple DTLS setup. As soon as the DTLS session is functional, the ACP peers will exchange ACP IPv6 packets as the payload of the DTLS transport connection. Any DTLS defined security association mechanisms such as re-keying are used as they would be for any transport application relying solely on DTLS.
As explained in the beginning of , there is no single secure channel mechanism mandated for all ACP nodes. Instead, this section defines two ACP profiles (baseline and constrained) for ACP nodes that do introduce such requirements. A baseline ACP node MUST support IPsec natively and MAY support IPsec via GRE. A constrained ACP node that cannot support IPsec MUST support DTLS. An ACP node connecting an area of constrained ACP nodes with an area of baseline ACP nodes must therefore support IPsec and DTLS and supports therefore the baseline and constrained profile. Explanation: Not all type of ACP nodes can or need to connect directly to each other or are able to support or prefer all possible secure channel mechanisms. For example, code space limited IoT devices may only support DTLS because that code exists already on them for end-to-end security, but high-end core routers may not want to support DTLS because they can perform IPsec in accelerated hardware but would need to support DTLS in an underpowered CPU forwarding path shared with critical control plane operations. This is not a deployment issue for a single ACP across these type of nodes as long as there are also appropriate gateway ACP nodes that support sufficiently many secure channel mechanisms to allow interconnecting areas of ACP nodes with a more constrained set of secure channel protocols. On the edge between IoT areas and high-end core networks, general-purpose routers that act as those gateways and that can support a variety of secure channel protocols is the norm already. ACP nodes need to specify in documentation the set of secure ACP mechanisms they support and should declare which profile they support according to above requirements. An ACP secure channel MUST immediately be terminated when the lifetime of any certificate in the chain used to authenticate the neighbor expires or becomes revoked. Note that this is not standard behavior in secure channel protocols such as IPsec because the certificate authentication only influences the setup of the secure channel in these protocols.
..............................ACP.............................. . . . /-GRASP-flooding-\ ACP GRASP instance . . / \ A . GRASP GRASP GRASP C . link-local unicast link-local P . multicast messages multicast . . messages | messages . . | | | . ............................................................... . v v v ACP security and transport . . | | | substrate for GRASP . . | | | . . | ACP GRASP | - ACP GRASP A . | Loopback | Loopback interface C . | interface | - ACP-cert auth P . | TLS | . . ACP GRASP | ACP GRASP - ACP GRASP virtual . . subnet1 | subnet2 virtual interfaces . . TCP | TCP . . | | | . ............................................................... . | | | ^^^ Users of ACP (GRASP/ASA) . . | | | ACP interfaces/addressing . . | | | . . | | | A . | ACP-Loopback Interf.| <- ACP Loopback interface C . | ACP-address | - address (global ULA) P . subnet1 | subnet2 <- ACP virtual interfaces . . link-local | link-local - link-local addresses . ............................................................... . | | | ACP VRF . . | RPL-routing | virtual routing and forwarding . . | /IP-Forwarding\ | A . | / \ | C . ACP IPv6 packets ACP IPv6 packets P . |/ \| . . IPsec/DTLS IPsec/DTLS - ACP-cert auth . ............................................................... | | Data-Plane | | | | - ACP secure channel link-local link-local - encapsulation addresses subnet1 subnet2 - Data-Plane interfaces | | ACP-Nbr1 ACP-Nbr2
GRASP unicast messages inside the ACP always use the ACP address. Link-local addresses from the ACP VRF must not be used inside objectives. GRASP unicast messages inside the ACP are transported via TLS according to execept that only TLS version 1.2 () or higher MUST be used - because there is no need for backward compatibility in the new use-case of ACP. Mutual authentication MUST use the ACP domain membership check defined in (). GRASP link-local multicast messages are targeted for a specific ACP virtual interface (as defined ) but are sent by the ACP into an ACP GRASP virtual interface that is constructed from the TCP connection(s) to the IPv6 link-local neighbor address(es) on the underlying ACP virtual interface. If the ACP GRASP virtual interface has two or more neighbors, the GRASP link-local multicast messages are replicated to all neighbor TCP connections. TLS for GRASP MUST offer TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 and TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 and MUST NOT offer options with less than 256bit AES or less than SHA384. TLS for GRASP MUST also include the "Supported Elliptic Curves" extension, it MUST support support the NIST P-256 (secp256r1) and P-384 (secp384r1(24)) curves . In addition, GRASP TLS clients SHOULD send an ec_point_formats extension with a single element, "uncompressed". For further interoperability recommendations, GRASP TLS implementations SHOULD follow . TCP and TLS connections for GRASP in the ACP use the IANA assigned TCP port for GRASP (7107). Effectively the transport stack is expected to be TLS for connections from/to the ACP address (e.g., global scope address(es)) and TCP for connections from/to link-local addresses on the ACP virtual interfaces. The latter ones are only used for flooding of GRASP messages.
Usage: Autonomic addresses are exclusively used for self-management functions inside a trusted domain. They are not used for user traffic. Communications with entities outside the trusted domain use another address space, for example normally managed routable address space (called "Data-Plane" in this document). Separation: Autonomic address space is used separately from user address space and other address realms. This supports the robustness requirement. Loopback-only: Only ACP Loopback interfaces (and potentially those configured for "ACP connect", see ) carry routable address(es); all other interfaces (called ACP virtual interfaces) only use IPv6 link local addresses. The usage of IPv6 link local addressing is discussed in . Use-ULA: For Loopback interfaces of ACP nodes, we use Unique Local Addresses (ULA), as defined in with L=1 (as defined in section 3.1 of ). Note that the random hash for ACP Loopback addresses uses the definition in and not the one of section 3.2.2. No external connectivity: They do not provide access to the Internet. If a node requires further reaching connectivity, it should use another, traditionally managed address scheme in parallel. Addresses in the ACP are permanent, and do not support temporary addresses as defined in . Addresses in the ACP are not considered sensitive on privacy grounds because ACP nodes are not expected to be end-user host. All ACP nodes are in one (potentially federated) administrative domain. They are assumed to be to be candidate hosts of ACP traffic amongst each other or transit thereof. There are no transit nodes less privileged to know about the identity of other hosts in the ACP. Therefore, ACP addresses do not need to be pseudo-random as discussed in . Because they are not propagated to untrusted (non ACP) nodes and stay within a domain (of trust), we also consider them not to be subject to scanning attacks. The ACP is based exclusively on IPv6 addressing, for a variety of reasons: Simplicity, reliability and scale: If other network layer protocols were supported, each would have to have its own set of security associations, routing table and process, etc. Autonomic functions do not require IPv4: Autonomic functions and autonomic service agents are new concepts. They can be exclusively built on IPv6 from day one. There is no need for backward compatibility. OAM protocols do not require IPv4: The ACP may carry OAM protocols. All relevant protocols (SNMP, TFTP, SSH, SCP, Radius, Diameter, ...) are available in IPv6. See also for how ACP could be made to interoperate with IPv4 only OAM.
The first 48-bits follow the ULA scheme, as defined in , to which a type field is added: "fd" identifies a locally defined ULA address. The 40-bits ULA "global ID" (term from ) for ACP addresses carried in the domain information field of domain certificates are the first 40-bits of the SHA256 hash of the routing subdomain from the same domain information field. In the example of , the routing subdomain is "" and the 40-bits ULA "global ID" 89b714f3db. When creating a new routing-subdomain for an existing autonomic network, it MUST be ensured, that rsub is selected so the resulting hash of the routing-subdomain does not collide with the hash of any pre-existing routing-subdomains of the autonomic network. This ensures that ACP addresses created by registrars for different routing subdomains do not collide with each others. To allow for extensibility, the fact that the ULA "global ID" is a hash of the routing subdomain SHOULD NOT be assumed by any ACP node during normal operations. The hash function is only executed during the creation of the certificate. If BRSKI is used then the BRSKI registrar will create the domain information field in response to the EST Certificate Signing Request (CSR) Attribute Request message by the pledge. Establishing connectivity between different ACP (different acp-domain-name) is outside the scope of this specification. If it is being done through future extensions, then the rsub of all routing-subdomains across those autonomic networks need to be selected so the resulting routing-subdomain hashes do not collide. For example a large cooperation with its own private Trust Anchor may want to create different autonomic networks that initially should not be able to connect but where the option to do so should be kept open. When taking this future possibility into account, it is easy to always select rsub so that no collisions happen. Type: This field allows different address sub-schemes. This addresses the "upgradability" requirement. Assignment of types for this field will be maintained by IANA. The sub-scheme may imply a range or set of addresses assigned to the node, this is called the ACP address range/set and explained in each sub-scheme. Please refer to and for further explanations why the following Sub-Addressing schemes are used and why multiple are necessary. The following summarizes the addressing schemes:
+------+-----+----------------+-------+------------+ | type | Z | name | F-bit | V-bit size | +------+-----+----------------+-------+------------+ | 0x00 | 0 | ACP Zone | N/A | 1 bit | +------+-----+----------------+-------+------------+ | 0x00 | 1 | ACP Manual | N/A | 1 bit | +------+-----+----------------+-------+------------+ | 0x01 | N/A | VLong-ASA | 0 | 8-bits | +------+-----+----------------+-------+------------+ | 0x01 | N/A | VLong-ACP-edge | 1 | 16-bits | +------+-----+----------------+-------+------------+
The sub-scheme defined here is defined by the Type value 00b (zero) in the base scheme and 0 in the Z bit.
64 64 +-----------------+---+---------++-----------------------------+---+ | (base scheme) | Z | Zone-ID || Node-ID | | | | || Registrar-ID | Node-Number| V | +-----------------+---+---------++--------------+--------------+---+ 50 1 13 48 15 1
The fields are defined as follows: Zone-ID: If set to all zero bits: The Node-ID bits are used as an identifier (as opposed to a locator). This results in a non-hierarchical, flat addressing scheme. Any other value indicates a zone. See on how this field is used in detail. Z: MUST be 0. Node-ID: A unique value for each node. The 64-bit Node-ID is derived and composed as follows: Registrar-ID (48-bit): A number unique inside the domain that identifies the ACP registrar which assigned the Node-ID to the node. A MAC address of the ACP registrar can be used for this purpose. Node-Number: A number which is unique for a given ACP registrar, to identify the node. This can be a sequentially assigned number. V (1-bit): Virtualization bit: 0: Indicates the ACP itself ("ACP node base system); 1: Indicates the optional "host" context on the ACP node (see below). In the ACP Zone Addressing Sub-Scheme, the ACP address in the certificate has Zone-ID and V fields as all zero bits. The ACP address set includes addresses with any Zone-ID value and any V value. The "Node-ID" itself is unique in a domain (i.e., the Zone-ID is not required for uniqueness). Therefore, a node can be addressed either as part of a flat hierarchy (Zone-ID = 0), or with an aggregation scheme (any other Zone-ID). An address with Zone-ID = 0 is an identifier, with a Zone-ID !=0 it is a locator. See for more details. The Virtual bit in this sub-scheme allows the easy addition of the ACP as a component to existing systems without causing problems in the port number space between the services in the ACP and the existing system. V:0 is the ACP router (autonomic node base system), V:1 is the host with pre-existing transport endpoints on it that could collide with the transport endpoints used by the ACP router. The ACP host could for example have a p2p virtual interface with the V:0 address as its router into the ACP. Depending on the software design of ASAs, which is outside the scope of this specification, they may use the V:0 or V:1 address. The location of the V bit(s) at the end of the address allows the announcement of a single prefix for each ACP node. For example, in a network with 20,000 ACP nodes, this avoid 20,000 additional routes in the routing table.
The Zone-ID allows for the introduction of route prefixes in the addressing scheme. Zone-ID = 0 is the default addressing scheme in an ACP domain. Every ACP node with a Zone Addressing Sub-Scheme address MUST respond to its ACP address with Zone-ID = 0. Used on its own this leads to a non-hierarchical address scheme, which is suitable for networks up to a certain size. Zone-ID = 0 addresses act as identifiers for the nodes, and aggregation of these address in the ACP routing table is not possible. If aggregation is required, the 13-bit Zone-ID value allows for up to 8191 zones. The allocation of Zone-ID's may either happen automatically through a to-be-defined algorithm; or it could be configured and maintained explicitly. If a node learns (see ) that it is part of a zone, it MUST also respond to its ACP address with that Zone-ID. In this case the ACP Loopback is configured with two ACP addresses: One for Zone-ID = 0 and one for the assigned Zone-ID. This method allows for a smooth transition between a flat addressing scheme and a hierarchical one. A node knowing it is in a zone MUST use that Zone-ID != 0 address in GRASP locator fields. This eliminates the use of the identifier address (Zone-ID = 0) in forwarding and the need for network wide reachability of those non-aggregable identifier addresses. Zone-ID != 0 addresses are assumed to be aggregable in routing/forwarding based on how they are allocated in the ACP topology. Note: The Zone-ID is one method to introduce structure or hierarchy into the ACP. Another way is the use of the routing subdomain field in the ACP that leads to multiple /48 Global IDs within an ACP domain. Note: Zones and Zone-ID as defined here are not related to zones or zone_id. ACP zone addresses are not scoped (reachable only from within an RFC4007 zone) but reachable across the whole ACP. An RFC4007 zone_id is a zone index that has only local significance on a node, whereas an ACP Zone-ID is an identifier for an ACP zone that is unique across that ACP.
The sub-scheme defined here is defined by the Type value 00b (zero) in the base scheme and 1 in the Z bit.
The fields are defined as follows: Subnet-ID: Configured subnet identifier. Z: MUST be 1. Interface Identifier. This sub-scheme is meant for "manual" allocation to subnets where the other addressing schemes cannot be used. The primary use case is for assignment to ACP connect subnets (see ). "Manual" means that allocations of the Subnet-ID need to be done today with pre-existing, non-autonomic mechanisms. Every subnet that uses this addressing sub-scheme needs to use a unique Subnet-ID (unless some anycast setup is done). The Z bit field was added to distinguish Zone addressing and manual addressing sub-schemes without requiring one more bit in the base scheme and therefore allowing for the Vlong scheme (described below) to have one more bit available. Manual addressing sub-scheme addresses SHOULD NOT be used in ACP domain certificates. Any node capable to build ACP secure channels and permitted by Registrar policy to participate in building ACP secure channels SHOULD receive an ACP address (prefix) from one of the other ACP addressing sub-schemes. Nodes not capable (or permitted) to participate in ACP secure channels can connect to the ACP via ACP connect interfaces of ACP edge nodes (see ), without setting up an ACP secure channel. Their ACP domain certificate MUST include an empty acp-address to indicate that their ACP domain certificate is only usable for non- ACP secure channel authentication, such as end-to-end transport connections across the ACP or Data-Plane. Address management of ACP connect subnets is done using traditional assignment methods and existing IPv6 protocols. See for details.
50 78 +---------------------++-----------------------------+----------+ | (base scheme) || Node-ID | | || Registrar-ID |F| Node-Number| V | +---------------------++--------------+--------------+----------+ 50 46 1 23/15 8/16
This addressing scheme foregoes the Zone-ID field to allow for larger, flatter routed networks (e.g., as in IoT) with 8421376 Node-Numbers (2^23+2^15). It also allows for up to 2^16 (i.e. 65536) different virtualized addresses within a node, which could be used to address individual software components in an ACP node. The fields are the same as in the Zone-ID sub-scheme with the following refinements: F: format bit. This bit determines the format of the subsequent bits. V: Virtualization bit: this is a field that is either 8 or 16 bits. For F=0, it is 8 bits, for F=1 it is 16 bits. The V bits are assigned by the ACP node. In the ACP certificate's ACP address , the V-bits are always set to 0. Registrar-ID: To maximize Node-Number and V, the Registrar-ID is reduced to 46-bits. This still permits the use of the MAC address of an ACP registrar by removing the V and U bits from the 48-bits of a MAC address (those two bits are never unique, so they cannot be used to distinguish MAC addresses). The Node-Number is unique to each ACP node. There are two formats for the Node-Number. When F=0, the node-number is 23 bits, for F=1 it is 15 bits. Each format of node-number is considered to be in a unique number space. The F=0 bit format addresses are intended to be used for "general purpose" ACP nodes that would potentially have a limited number (< 256) of clients (ASA/Autonomic Functions or legacy services) of the ACP that require separate V(irtual) addresses. The F=1 bit Node-Numbers are intended for ACP nodes that are ACP edge nodes (see ) or that have a large number of clients requiring separate V(irtual) addresses. For example large SDN controllers with container modular software architecture (see ). In the Vlong addressing sub-scheme, the ACP address in the certificate has all V field bits as zero. The ACP address set for the node includes any V value.
ACP registrars are responsible to enroll candidate ACP nodes with ACP domain certificates and associated trust point(s). They are also responsible that an ACP domain information field is included in the ACP domain certificate carrying the ACP domain name and the ACP nodes ACP address prefix. This address prefix is intended to persist unchanged through the lifetime of the ACP node. Because of the ACP addressing sub-schemes, an ACP domain can have multiple distributed ACP registrars that do not need to coordinate for address assignment. ACP registrars can also be sub-CAs, in which case they can also assign ACP domain certificates without dependencies against a (shared) root-CA (except during renewals of their own certificates). ACP registrars are PKI registration authorities (RA) enhanced with the handling of the ACP domain certificate specific fields. They request certificates for ACP nodes from a Certificate Authority through any appropriate mechanism (out of scope in this document, but required to be BRSKI for ANI registrars). Only nodes that are trusted to be compliant with the requirements against registrar described in this section must be given the necessary credentials to perform this RA function, such as credentials for the BRSKI connection to the CA for ANI registrars.
Any protocols or mechanisms may be used as ACP registrars, as long as the resulting ACP certificate and trust anchors allow to perform the ACP domain membership described in with other ACP domain members, and meet the ACP addressing requirements for its ACP domain information field as described further below in this section. An ACP registrar could be a person deciding whether to enroll a candidate ACP node and then orchestrating the enrollment of the ACP certificate and associated trust anchor, using command line or web based commands on the candidate ACP node and trust anchor to generate and sign the ACP domain certificate and configure certificate and trust anchors onto the node. The only currently defined protocol for ACP registrars is BRSKI (). When BRSKI is used, the ACP nodes are called ANI nodes, and the ACP registrars are called BRSKI or ANI registrars. The BRSKI specification does not define the handling of the ACP domain information field because the rules do not depend on BRSKI but apply equally to any protocols/mechanisms an ACP registrar may use.
ACP registrars MUST NOT allocate ACP address prefixes to ACP nodes via the ACP domain information field that would collide with the ACP address prefixes of other ACP nodes in the same ACP domain. This includes both prefixes allocated by the same ACP registrar to different ACP nodes as well as prefixes allocated by other ACP registrars for the same ACP domain. For this purpose, an ACP registrar MUST have one or more unique 46-bit identifiers called Registrar-IDs used to allocate ACP address prefixes. The lower 46-bits of a EUI-48 MAC addresses are globally unique 46 bit identifiers, so ACP registrars with known unique EUI-48 MAC addresses can use these as Registrar-IDs. Registrar-IDs do not need to be globally unique but only unique across the set of ACP registrars for an ACP domain, so other means to assign unique Registrar-IDs to ACP registrars can be used, such as configuration on the ACP registrars. When the candidate ACP device (called Pledge in BRSKI) is to be enrolled into an ACP domain, the ACP registrar needs to allocate a unique ACP address to the node and ensure that the ACP certificate gets a domain information field () with the appropriate information - ACP domain-name, ACP-address, and so on. If the ACP registrar uses BRSKI, it signals the ACP domain information field to the Pledge via the EST /csrattrs command (see , section 5.9.2 - "EST CSR Attributes"). [RFC Editor: please update reference to section 5.9.2 accordingly with latest BRSKI draft at time of publishing, or RFC]
The ACP registrar selects for the candidate ACP node a unique address prefix from an appropriate ACP addressing sub-scheme, either a zone addressing sub-scheme prefix (see ), or a Vlong addressing sub-scheme prefix (see ). The assigned ACP address prefix encoded in the domain information field of the ACP domain certificate indicates to the ACP node its ACP address information. The sub-addressing scheme indicates the prefix length: /127 for zone address sub-scheme, /120 or /112 for Vlong address sub-scheme. The first address of the prefix is the ACP address. All other addresses in the prefix are for other uses by the ACP node as described in the zone and Vlong addressing sub scheme sections. The ACP address prefix itself is then signaled by the ACP node into the ACP routing protocol (see ) to establish IPv6 reachability across the ACP. The choice of addressing sub-scheme and prefix-length in the Vlong address sub-scheme is subject to ACP registrar policy. It could be an ACP domain wide policy, or a per ACP node or per ACP node type policy. For example, in BRSKI, the ACP registrar is aware of the IDevID of the candidate ACP node, which contains a "serialNnumber" that is typically indicating the node's vendor and device type and can be used to drive a policy selecting an appropriate addressing sub-scheme for the (class of) node(s). ACP registrars SHOULD default to allocate ACP zone sub-address scheme addresses with Zone-ID 0. Allocation and use of zone sub-addresses with Zone-ID != 0 is outside the scope of this specification because it would need to go along with rules for extending ACP routing to multiple zones, which is outside the scope of this specification. ACP registrars that can use the IDevID of a candidate ACP device SHOULD be able to choose the zone vs. Vlong sub-address scheme for ACP nodes based on the "serialNumber" of the IDevID, for example by the PID (Product Identifier) part which identifies the product type, or the complete "serialNumber". In a simple allocation scheme, an ACP registrar remembers persistently across reboots its currently used Registrar-ID and for each addressing scheme (zone with Zone-ID 0, Vlong with /112, Vlong with /120), the next Node-Number available for allocation and increases it during successful enrollment to an ACP node. In this simple allocation scheme, the ACP registrar would not recycle ACP address prefixes from no longer used ACP nodes.
When an ACP domain certificate is renewed or rekeyed via EST or other mechanisms, the ACP address/prefix in the ACP domain information field MUST be maintained unless security issues or violations of the unique address assignment requirements exist or are suspected by the ACP registrar. ACP address information SHOULD be maintained even when the renewing/rekeying ACP registrar is not the same as the one that enrolled the prior ACP certificate. See for an example. ACP address information SHOULD also be maintained even after an ACP certificate did expire or failed. See and .
The choosen RPL profile is one that expects a fairly reliable network with reasonably fast links so that RPL convergence will be triggered immediately upon recognition of link failure/recovery. The profile is also designed to not require any RPL Data-Plane artifacts (such as defined in ). This is largely driven by the desire to avoid introducing the required Hop-by-Hop headers into the ACP forwarding plane, especially to support devices with silicon forwarding planes that cannot support insertion/removal of these headers in silicon or hop-by-hop forwarding based on them. Note: Insertion/removal of headers by a (potentially silicon based) ACP node would be be necessary when senders/receivers of ACP packets are legacy NOC devices connected via ACP connect (see to the ACP. Their connectivity can be handled in RPL as non-RPL-aware leafs (or "Internet") according to the Data-Plane architecture explained in . To avoid Data-Plane artefacts, the profile uses a simple destination prefix based routing/forwarding table. To achieve this, the profiles uses only one RPL instanceID. This single instanceID can contain only one Destination Oriented Directed Acyclic Graph (DODAG), and the routing/forwarding table can therefore only calculate a single class of service ("best effort towards the primary NOC/root") and cannot create optimized routing paths to accomplish latency or energy goals between any two nodes. Consider a network that has multiple NOCs in different locations. Only one NOC will become the DODAG root. Traffic to and from other NOCs has to be sent through the DODAG (shortest path tree) rooted in the primary NOC. Depending on topology, this can be an annoyance from a latency point of view or from minimizing network path resources, but this is deemed to be acceptable given how ACP traffic is "only" network management/control traffic. Using a single instanceID/DODAG does not introduce a single point of failure, as the DODAG will reconfigure itself when it detects data-plane forwarding failures including choosing a different root when the primary one fails. See for more details. The benefit of this profile, especially compared to other IGPs is that it does not calculate routes for node reachable through the same interface as the DODAG root. This RPL profile can therefore scale to much larger number of ACP nodes in the same amount of compute and memory than other routing protocols. Especially on nodes that are leafs of the topology or those close to those leafs. The lack of RPL Packet Information (RPI, the IPv6 header for RPL defined by ), means that the Data-Plane will have no rank value that can be used to detect loops. As a result, traffic may loop until the time-to-live (TTL) of the packet reaches zero. This is the same behavior as that of other IGPs that do not have the Data-Plane options of RPL. Since links in the ACP are assumed to be mostly reliable (or have link layer protection against loss) and because there is no stretch according to , loops caused by RPL routing packet loss should be exceedingly rare. There are a variety of mechanisms possible in RPL to further avoid temporary loops: DODAG Information Objects (DIOs) SHOULD be sent 2...3 times to inform children when losing the last parent. The technique in section (Detaching) SHOULD be favored over that in section, (Poisoning) because it allows local connectivity. Nodes SHOULD select more than one parent, at least 3 if possible, and send Destination Advertisement Objects (DAO)s to all of them in parallel. Additionally, failed ACP tunnels can be quickly discovered trough the secure channel protocol mechanisms such as IKEv2 Dead Peer Detection. This can function as a replacement for a Low-power and Lossy Networks' (LLN's) Expected Transmission Count (ETX) feature that is not used in this profile. A failure of an ACP tunnel should imediately signal the RPL control plane to pick a different parent.
Single RPL instance. Default RPLInstanceID = 0.
Proactive, aggressive DAO state maintenance: Use K-flag in unsolicited DAO indicating change from previous information (to require DAO-ACK). Retry such DAO DAO-RETRIES(3) times with DAO- ACK_TIME_OUT(256ms) in between.
Not used.
Every ACP node (RPL node) announces an IPv6 prefix covering the address(es) used in the ACP node. The prefix length depends on the chosen addressing sub-scheme of the ACP address provisioned into the certificate of the ACP node, e.g., /127 for Zone Addressing Sub-Scheme or /112 or /120 for Vlong addressing sub-scheme. See for more details. Every ACP node MUST install a black hole (aka null) route for whatever ACP address space that it advertises (i.e.: the /96 or /127). This is avoid routing loops for addresses that an ACP node has not (yet) used.
Administrative Preference (, 3.2.6 – to become root): Indicated in DODAGPreference field of DIO message. Explicit configured ”root”: 0b100 ACP registrar (Default): 0b011 ACP-connect (non-registrar): 0b010 Default: 0b001.
Because RPL minimizes the size of the routing and forwarding table, prefixes reachable through the same interface as the RPL root are not known on every ACP node. Therefore traffic to unknown destination addresses can only be discovered at the RPL root. The RPL root SHOULD have attach safe mechanisms to operationally discover and log such packets. As this requirement raises additional data plane requirements, it does not apply to nodes where the administrative parameter to become root () can always only be 0b001, e.g.: the node does not support explicit configuration to be root, or to be ACP registrar or to have ACP-connect functionality. If an ACP network is degraded to the point where there are no nodes that could be configured roots, ACP registrars or ACP-connect nodes, traffic to unknown destinations could not be diagnosed, but in the absence of any intelligent nodes supporting other than 0b001 administrative preference, there is likely also no diagnostic function possible.
Data-Plane "native" (no ACP) . +--------+ +----------------+ . +-------------+ | ACP | |ACP Edge Node | . | | | Node | | | v | | | |-------|...[ACP VRF]....+-----------------| |+ | | ^ |. | | NOC Device || | | . | .[Data-Plane]..+-----------------| "NMS hosts" || | | . | [ ] | . ^ | || +--------+ . +----------------+ . . +-------------+| . . . +-------------+ . . . Data-Plane "native" . ACP "native" (unencrypted) + ACP auto-negotiated . "ACP connect subnet" and encrypted . ACP connect interface e.g., "VRF ACP native" (config)
Combined ACP and Data-Plane interface . +--------+ +--------------------+ . +--------------+ | ACP | |ACP Edge No | . | NMS Host(s) | | Node | | | . | / Software | | | | [ACP ]. | . | |+ | | | .[VRF ] .[VRF ] | v | "ACP address"|| | +-------+. .[Select].+--------+ "Date Plane || | | ^ | .[Data ]. | | Address(es)"|| | | . | [Plane] | | || | | . | [ ] | +--------------+| +--------+ . +--------------------+ +--------------+ . Data-Plane "native" and + ACP auto-negotiated/encrypted
GRASP can and should be possible to use across ACP connect interfaces, especially in the architectural correct solution when it is used as a mechanism to connect Software (e.g., ASA or legacy NMS applications) to the ACP. Given how the ACP is the security and transport substrate for GRASP, the requirements for devices connected via ACP connect is that those are equivalently (if not better) secured against attacks and run only software that is equally (if not better) protected, known (or trusted) not to be malicious and accordingly designed to isolate access to the ACP against external equipment. The difference in security is that cryptographic security of the ACP secure channel is replaced by required physical security of the network connection between an ACP edge node and the NMS or other host reachable via the ACP connect interface. Node integrity too is expected to be easier because the ACP connect node, the ACP connect link and the nodes connecting to it must be in a contiguous secure location, hence assuming there can be no physical attack against the devices. When using "Combined ACP and Data-Plane Interfaces", care must be taken that only GRASP messages intended for the ACP GRASP domain received from Software or NMS Hosts are forwarded by ACP edge nodes. Currently there is no definition for a GRASP security and transport substrate beside the ACP, so there is no definition how such Software/NMS Host could participate in two separate GRASP Domains across the same subnet (ACP and Data-Plane domains). At current it is assumed that all GRASP packets on a Combined ACP and Data-Plane interface belong to the GRASP ACP Domain. They must all use the ACP IPv6 addresses of the Software/NMS Hosts. The link-local IPv6 addresses of Software/NMS Hosts (used for GRASP M_DISCOVERY and M_FLOOD messages) are also assumed to belong to the ACP address space.
Explicit configuration of a remote-peer according to this ABNF provides all the information to build a secure channel without requiring a tunnel to that peer and running DULL GRASP inside of it. The configuration includes the parameters otherwise signaled via DULL GRASP: local address, remote (peer) locator and method. The differences over DULL GRASP local neighbor discovery and secure channel creation are as follows: The local and remote address can be IPv4 or IPv6 and are typically global scope addresses. The VRF across which the connection is built (and in which local-addr exists) can to be specified. If vrf is not specified, it is the default VRF on the node. In DULL GRASP the VRF is implied by the interface across which DULL GRASP operates. If local address is "any", the local address used when initiating a secure channel connection is decided by source address selection ( for IPv6). As a responder, the connection listens on all addresses of the node in the selected VRF. Configuration of port is only required for methods where no defaults exist (e.g., "DTLS"). If remote address is "any", the connection is only a responder. It is a "hub" that can be used by multiple remote peers to connect simultaneously - without having to know or configure their addresses. Example: Hub site for remote "spoke" sites reachable over the Internet. Pmtu should be configurable to overcome issues/limitations of Path MTU Discovery (PMTUD). IKEv2/IPsec to remote peers should support the optional NAT Traversal (NAT-T) procedures.
The ACP is self-healing: New neighbors will automatically join the ACP after successful validation and will become reachable using their unique ULA address across the ACP. When any changes happen in the topology, the routing protocol used in the ACP will automatically adapt to the changes and will continue to provide reachability to all nodes. The ACP tracks the validity of peer certificates and tears down ACP secure channels when a peer certificate has expired. When short-lived certificates with lifetimes in the order of OCSP/CRL refresh times are used, then this allows for removal of invalid peers (whose certificate was not renewed) at similar speeds as when using OCSP/CRL. The same benefit can be achieved when using CRL/OCSP, periodically refreshing the revocation information and also tearing down ACP secure channels when the peer's (long-lived) certificate is revoked. There is no requirement against ACP implementations to require this enhancement though to keep the mandatory implementations simpler. The ACP can also sustain network partitions and mergers. Practically all ACP operations are link local, where a network partition has no impact. Nodes authenticate each other using the domain certificates to establish the ACP locally. Addressing inside the ACP remains unchanged, and the routing protocol inside both parts of the ACP will lead to two working (although partitioned) ACPs. There are few central dependencies: A certificate revocation list (CRL) may not be available during a network partition; a suitable policy to not immediately disconnect neighbors when no CRL is available can address this issue. Also, an ACP registrar or Certificate Authority might not be available during a partition. This may delay renewal of certificates that are to expire in the future, and it may prevent the enrollment of new nodes during the partition. Highly resilient ACP designs can be built by using ACP registrars with embedded sub-CA, as outlined in . As long as a partition is left with one or more of such ACP registrars, it can continue to enroll new candidate ACP nodes as long as the ACP registrar's sub-CA certificate does not expire. Because the ACP addressing relies on unique Registrar-IDs, a later re-merge of partitions will also not cause problems with ACP addresses assigned during partitioning. After a network partition, a re-merge will just establish the previous status, certificates can be renewed, the CRL is available, and new nodes can be enrolled everywhere. Since all nodes use the same trust anchor(s), a re-merge will be smooth. Merging two networks with different trust anchors requires the ACP nodes to trust the union of Trust Anchors. As long as the routing-subdomain hashes are different, the addressing will not overlap, which only happens in the unlikely event of a 40-bit hash collision in SHA256 (see ). Note that the complete mechanisms to merge networks is out of scope of this specification. It is also highly desirable for implementation of the ACP to be able to run it over interfaces that are administratively down. If this is not feasible, then it might instead be possible to request explicit operator override upon administrative actions that would administratively bring down an interface across which the ACP is running. Especially if bringing down the ACP is known to disconnect the operator from the node. For example any such down administrative action could perform a dependency check to see if the transport connection across which this action is performed is affected by the down action (with default RPL routing used, packet forwarding will be symmetric, so this is actually possible to check).
The following sections document important operational aspects of the ACP. They are not normative because they do not impact the interoperability between components of the ACP, but they include recommendations/requirements for the internal operational model beneficial or necessary to achieve the desired use-case benefits of the ACP (see ). describes recommended operator diagnostics capabilities of ACP nodes. The have been derived from diagnostic of a commercially available ACP implementation. describes high level how an ACP registrar needs to work, what its configuration parameters are and specific issues impacting the choices of deployment design due to renewal and revocation issues. It describes a model where ACP Registrars have their own sub-CA to provide the most distributed deployment option for ACP Registrars, and it describes considerations for centralized policy control of ACP Registrar operations. describes suggested ACP node behavior and operational interfaces (configuration options) to manage the ACP in so-called greenfield devices (previously unconfigured) and brownfield devices (preconfigured). The recommendations and suggestions of this chapter were derived from operational experience gained with a commercially available pre-standard ACP implementation.
Even though ACP and ANI in general are taking out many manual configuration mistakes through their automation, it is important to provide good diagnostics for them. The basic diagnostics is support of (yang) data models representing the complete (auto-)configuration and operational state of all components: BRSKI, GRASP, ACP and the infrastructure used by them: TLS/DTLS, IPsec, certificates, trust anchors, time, VRF and so on. While necessary, this is not sufficient: Simply representing the state of components does not allow operators to quickly take action - unless they do understand how to interpret the data, and that can mean a requirement for deep understanding of all components and how they interact in the ACP/ANI. Diagnostic supports should help to quickly answer the questions operators are expected to ask, such as "is the ACP working correctly?", or "why is there no ACP connection to a known neighboring node?" In current network management approaches, the logic to answer these questions is most often built as centralized diagnostics software that leverages the above mentioned data models. While this approach is feasible for components utilizing the ANI, it is not sufficient to diagnose the ANI itself: Developing the logic to identify common issues requires operational experience with the components of the ANI. Letting each management system define its own analysis is inefficient. When the ANI is not operating correctly, it may not be possible to run diagnostics from remote because of missing connectivity. The ANI should therefore have diagnostic capabilities available locally on the nodes themselves. Certain operations are difficult or impossible to monitor in real-time, such as initial bootstrap issues in a network location where no capabilities exist to attach local diagnostics. Therefore it is important to also define means of capturing (logging) diagnostics locally for later retrieval. Ideally, these captures are also non-volatile so that they can survive extended power-off conditions - for example when a device that fails to be brought up zero-touch is being sent back for diagnostics at a more appropriate location. The most simple form of diagnostics answering questions such as the above is to represent the relevant information sequentially in dependency order, so that the first non-expected/non-operational item is the most likely root cause. Or just log/highlight that item. For example: Q: Is ACP operational to accept neighbor connections: Check if any potentially necessary configuration to make ACP/ANI operational are correct (see for a discussion of such commands). Does the system time look reasonable, or could it be the default system time after clock chip battery failure (certificate checks depend on reasonable notion of time). Does the node have keying material - domain certificate, trust anchors. If no keying material and ANI is supported/enabled, check the state of BRSKI (not detailed in this example). Check the validity of the domain certificate: Does the certificate validate against the trust anchor? Has it been revoked? Was the last scheduled attempt to retrieve a CRL successful (e.g., do we know that our CRL information is up to date). Is the certificate valid: validity start time in the past, expiration time in the future? Does the certificate have a correctly formatted ACP domain information field? Was the ACP VRF successfully created? Is ACP enabled on one or more interfaces that are up and running? If all this looks good, the ACP should be running locally "fine" - but we did not check any ACP neighbor relationships. Question: why does the node not create a working ACP connection to a neighbor on an interface? Is the interface physically up? Does it have an IPv6 link-local address? Is it enabled for ACP? Do we successfully send DULL GRASP messages to the interface (link layer errors)? Do we receive DULL GRASP messages on the interface? If not, some intervening L2 equipment performing bad MLD snooping could have caused problems. Provide e.g., diagnostics of the MLD querier IPv6 and MAC address. Do we see the ACP objective in any DULL GRASP message from that interface? Diagnose the supported secure channel methods. Do we know the MAC address of the neighbor with the ACP objective? If not, diagnose SLAAC/ND state. When did we last attempt to build an ACP secure channel to the neighbor? If it failed, why: Did the neighbor close the connection on us or did we close the connection on it because the domain certificate membership failed? If the neighbor closed the connection on us, provide any error diagnostics from the secure channel protocol. If we failed the attempt, display our local reason: There was no common secure channel protocol supported by the two neighbors (this could not happen on nodes supporting this specification because it mandates common support for IPsec). The ACP domain certificate membership check () fails: The neighbor's certificate does not have the required trust anchor. Provide diagnostics which trust anchor it has (can identify whom the device belongs to). The neighbor's certificate does not have the same domain (or no domain at all). Diagnose domain-name and potentially other cert info. The neighbor's certificate has been revoked or could not be authenticated by OCSP. The neighbor's certificate has expired - or is not yet valid. Any other connection issues in e.g., IKEv2 / IPsec, DTLS?. Question: Is the ACP operating correctly across its secure channels? Are there one or more active ACP neighbors with secure channels? Is the RPL routing protocol for the ACP running? Is there a default route to the root in the ACP routing table? Is there for each direct ACP neighbor not reachable over the ACP virtual interface to the root a route in the ACP routing table? Is ACP GRASP running? Is at least one SRV.est objective cached (to support certificate renewal)? Is there at least one BRSKI registrar objective cached (in case BRSKI is supported) Is BRSKI proxy operating normally on all interfaces where ACP is operating? ... These lists are not necessarily complete, but illustrate the principle and show that there are variety of issues ranging from normal operational causes (a neighbor in another ACP domain) over problems in the credentials management (certificate lifetimes), explicit security actions (revocation) or unexpected connectivity issues (intervening L2 equipment). The items so far are illustrating how the ANI operations can be diagnosed with passive observation of the operational state of its components including historic/cached/counted events. This is not necessary sufficient to provide good enough diagnostics overall: The components of ACP and BRSKI are designed with security in mind but they do not attempt to provide diagnostics for building the network itself. Consider two examples: BRSKI does not allow for a neighboring device to identify the pledges certificate (IDevID). Only the selected BRSKI registrar can do this, but it may be difficult to disseminate information about undesired pledges from those BRSKI registrars to locations/nodes where information about those pledges is desired. The Link Layer Discovery Protocol (LLDP, ) disseminates information about nodes to their immediate neighbors, such as node model/type/software and interface name/number of the connection. This information is often helpful or even necessary in network diagnostics. It can equally considered to be too insecure to make this information available unprotected to all possible neighbors. An "interested adjacent party" can always determine the IDevID of a BRSKI pledge by behaving like a BRSKI proxy/registrar. Therefore the IDevID of a BRSKI pledge is not meant to be protected - it just has to be queried and is not signaled unsolicited (as it would be in LLDP) so that other observers on the same subnet can determine who is an "interested adjacent party".
As described in , the ACP addressing mechanism is designed to enable lightweight, distributed and uncoordinated ACP registrars that are providing ACP address prefixes to candidate ACP nodes by enrolling them with an ACP domain certificate into an ACP domain via any appropriate mechanism/protocol, automated or not. This section discusses informatively more details and options for ACP registrars.
The interactions of an ACP registrar outlined and above depend on the following parameters: A URL to the trust anchor (root CA) and credentials so that the ACP registrar can let the trust anchor sign candidate ACP member certificates. The ACP domain-name. The Registrar-ID to use. This could default to a MAC address of the ACP registrar. For recovery, the next-useable Node-IDs for zone (Zone-ID=0) sub-addressing scheme, for Vlong /112 and for Vlong /1120 sub-addressing scheme. These IDs would only need to be provisioned after recovering from a crash. Some other mechanism would be required to remember these IDs in a backup location or to recover them from the set of currently known ACP nodes. Policies if candidate ACP nodes should receive a domain certificate or not, for example based on the devices IDevID as in BRSKI. The ACP registrar may have a whitelist or blacklist of devices "serialNumbers" from their IDevID. Policies what type of address prefix to assign to a candidate ACP devices, based on likely the same information. For BRSKI or other mechanisms using vouchers: Parameters to determine how to retrieve vouchers for specific type of secure bootstrap candidate ACP nodes (such as MASA URLs), unless this information is automatically learned such as from the IDevID of candidate ACP nodes (as defined in BRSKI).
When an ACP node renews/rekeys its certificate, it may end up doing so via a different registrar (e.g., EST server) than the one it originally received its ACP domain certificate from, for example because that original ACP registrar is gone. The ACP registrar through which the renewal/rekeying is performed would by default trust the ACP domain information from the ACP nodes current ACP domain certificate and maintain this information so that the ACP node maintains its ACP address prefix. In EST renewal/rekeying, the ACP nodes current ACP domain certificate is signaled during the TLS handshake. This simple scenario has two limitations: The ACP registrars cannot directly assign certificates to nodes and therefore needs an "online" connection to the trust anchor (root CA). Recovery from a compromised ACP registrar is difficult. When an ACP registrar is compromised, it can insert for example conflicting ACP domain information and create thereby an attack against other ACP nodes through the ACP routing protocol. Even when such a malicious ACP registrar is detected, resolving the problem may be difficult because it would require identifying all the wrong ACP domain certificates assigned via the ACP registrar after it was compromised. And without additional centralized tracking of assigned certificates there is no way to do this.
In situations, where either of the above two limitations are an issue, ACP registrars could also be sub-CAs. This removes the need for connectivity to a root-CA whenever an ACP node is enrolled, and reduces the need for connectivity of such an ACP registrar to a root-CA to only those times when it needs to renew its own certificate. The ACP registrar would also now use its own (sub-CA) certificate to enroll and sign the ACP nodes certificates, and therefore it is only necessary to revoke a compromised ACP registrars sub-CA certificate. Alternatively one can let it expire and not renew it, when the certificate of the sub-CA is appropriately short-lived. As the ACP domain membership check verifies a peer ACP node's ACP domain certificate trust chain, it will also verify the signing certificate which is the compromised/revoked sub-CA certificate. Therefore ACP domain membership for an ACP node enrolled from a compromised and discovered ACP registrar will fail. ACP nodes enrolled by a compromised ACP registrar would automatically fail to establish ACP channels and ACP domain certificate renewal via EST and therefore revert to their role as a candidate ACP members and attempt to get a new ACP domain certificate from an ACP registrar - for example, via BRSKI. In result, ACP registrars that have an associated sub-CA makes isolating and resolving issues with compromised registrars easier. Note that ACP registrars with sub-CA functionality also can control the lifetime of ACP domain certificates easier and therefore also be used as a tool to introduce short lived certificates and not rely on CRL, whereas the certificates for the sub-CAs themselves could be longer lived and subject to CRL.
When using multiple, uncoordinated ACP registrars, several advanced operations are potentially more complex than with a single, resilient policy control backend, for example including but not limited to: Which candidate ACP node is permitted or not permitted into an ACP domain. This may not be a decision to be taken upfront, so that a per-"serialNumber" policy can be loaded into every ACP registrar. Instead, it may better be decided in real-time including potentially a human decision in a NOC. Tracking of all enrolled ACP nodes and their certificate information. For example in support of revoking individual ACP nodes certificates. More flexible policies what type of address prefix or even what specific address prefix to assign to a candidate ACP node. These and other operations could be introduced more easily by introducing a centralized Policy Management System (PMS) and modifying ACP registrar behavior so that it queries the PMS for any policy decision occurring during the candidate ACP node enrollment process and/or the ACP node certificate renewal process. For example, which ACP address prefix to assign. Likewise the ACP registrar would report any relevant state change information to the PMS as well, for example when a certificate was successfully enrolled onto a candidate ACP node.
A "greenfield" node is one that did not have any prior configuration. For greenfield nodes, only "ANI enable" is relevant. If another mechanism than BRSKI is used to (zero-touch) bootstrap a node, then it is up to that mechanism to provision domain certificates and to set global "ACP enable" as desired. Nodes supporting full ANI functionality set "ANI enable" automatically when they decide that they are greenfield, e.g., that they are powering on from factory condition. They will then put all native interfaces into "admin down" state and start to perform BRSKI pledge functionality - and once a domain certificate is enrolled they automatically enable ACP. Attempts for BRSKI pledge operations in greenfield state should terminate automatically when another method of configuring the node is used. Methods that indicate some form of physical possession of the device such as configuration via the serial console port could lead to immediate termination of BRSKI, while other parallel auto configuration methods subject to remote attacks might lead to BRSKI termination only after they were successful. Details of this may vary widely over different type of nodes. When BRSKI pledge operation terminates, this will automatically unset "ANI enable" and should terminate any temporarily needed state on the device to perform BRSKI - DULL GRASP, BRSKI pledge and any IPv6 configuration on interfaces.
There is no desirable configuration for the ACP. Instead, all parameters that need to be configured in support of the ACP are limitations of the solution, but they are only needed in cases where not all components are made autonomic. Whereever this is necessary, it relies on pre-existing mechanisms for configuration such as CLI or YANG () data models. The most important examples of such configuration include: When ACP nodes do not support an autonomic way to receive an ACP domain certificate, for example BRSKI, then such certificate needs to be configured via some pre-existing mechanisms outside the scope of this specification. Today, router have typically a variety of mechanisms to do this. Certificate maintenance requires PKI functions. Discovery of these functions across the ACP is automated (see ), but their configuration is not. When non-ACP capable nodes such as pre-existing NMS need to be physically connected to the ACP, the ACP node to which they attach needs to be configured with ACP-connect according to . It is also possible to use that single physical connection to connect both to ACP and the data-plane of the network as explained in . When devices are not autonomically bootstrapped, explicit configuration to enable the ACP needs to be applied. See . When the ACP needs to be extended across interfacess other than L2, the ACP as defined in this document can not autodiscover candidate neighbors automatically. Remote neighbors need to be configured, see . Once the ACP is operating, any further configuration for the data-plane can be configured more reliably across the ACP itself because the ACP provides addressing and connectivity (routing) independent of the data-plane itself. For this, the configuration methods simply need to also allow to operate across the ACP VRF - netconf, ssh or any other method. The ACP also provides additional security through its hop-by-hop encryption for any such configuration operations: Some legacy configuration methods (SNMP, TFTP, HTTP) may not use end-to-end encryption, and most of the end-to-end secured configuration methods still allow for easy passive observation along the path about configuration taking place (transport flows, port numbers, IP addresses). The ACP can and should equally be used as the transport to configure any of the aforemention non-automic components of the ACP, but in that case, the same caution needs to be exercised as with data-plane configuration without ACP: Misconfiguration may cause the configuring entity to be disconnected from the node it configures - for example when incorrectly unconfiguring a remote ACP neighbor through which the configured ACP node is reached.
After seeding an ACP by configuring at least one ACP registrar with routing-subdomain and a CA, an ACP is self-protecting and there is no need to apply configuration to make it secure (typically the ACP Registrar doubles as EST server for certificate renewal). Its security therefore does not depend on configuration. This does not include workarounds for non-autonomic components as explained in . See for details of how the ACP protects itself against attacks from the outside and to a more limited degree from the inside as well. However, the security of the ACP depends on a number of other factors: The usage of domain certificates depends on a valid supporting PKI infrastructure. If the chain of trust of this PKI infrastructure is compromised, the security of the ACP is also compromised. This is typically under the control of the network administrator. Every ACP registrar is criticial infrastructure that needs to be hardened against attacks, similar to a CA. A malicious registrar can enroll enemy plegdes to an ACP network or break ACP routing by duplicate ACP address assignment to pledges via their ACP domain certificates. Security can be compromised by implementation errors (bugs), as in all products. There is no prevention of source-address spoofing inside the ACP. This implies that if an attacker gains access to the ACP, it can spoof all addresses inside the ACP and fake messages from any other node. The ACP is designed to enable automation of current network management and future autonomic peer-to-peer/distributed network automation. Any ACP member can send ACP IPv6 packet to other ACP members and announce via ACP GRASP services to all ACP members without depenency against centralized components. The ACP relies on peer-to-peer authentication and authorization using ACP certificates. This security model is necessary to enable the autonomic ad-hoc any-to-any connectivity between ACP nodes. It provides infrastructure protection through hop by hop authentication and encryption - without relying on third parties. For any services where this complete autonomic peer-to-peer group security model is appropriate, the ACP domain certificate can also be used unchanged. For example for any type of data-plane routing protocol security. This ACP security model is designed primarily to protect against attack from the outside, but not against attacks from the inside. To protect against spoofing attacks from compromised on-path ACP nodes, end-to-end encryption inside the ACP is used by new ACP signaling: GRASP across the ACP using TLS. The same is expected from any non-legacy services/protocols using the ACP. Because no group-keys are used, there is no risk for impacted nodes to access end-to-end encrypted traffic from other ACP nodes. Attacks from impacted ACP nodes against the ACP are more difficult than against the data-plane because of the autoconfiguration of the ACP and the absence of configuration options that could be abused that allow to change/break ACP behavior. This is excluding configuration for workaround in support of non-autonomic components. Mitigation against compromised ACP members is possible through standard automated certificate management mechanisms including revocation and non-renewal of short-lived certificates. In this version of the specification, there are no further optimization of these mechanisms defined for the ACP (but see ). Higher layer service built using ACP domain certificates should not solely rely on undifferentiated group security when another model is more appropriate/more secure. For example central network configuration relies on a security model where only few especially trusted nodes are allowed to configure the data-plane of network nodes (CLIL, Netconf). This can be done through ACP domain certificates by differentiating them and introduce roles. See . Fundamentally, security depends on avoiding operator and network operations automation mistakes, implementation and architecture. Autonomic approaches such as the ACP largely eliminate operator mistakes and make it easier to recover from network operations mistakes. Implementation and architectural mistakes are still possible, as in all networking technologies. Many details of ACP are designed with security in mind and discussed elsewhere in the document: IPv6 addresses used by nodes in the ACP are covered as part of the node's domain certificate as described in . This allows even verification of ownership of a peer's IPv6 address when using a connection authenticated with the domain certificate. The ACP acts as a security (and transport) substrate for GRASP inside the ACP such that GRASP is not only protected by attacks from the outside, but also by attacks from compromised inside attackers - by relying not only on hop-by-hop security of ACP secure channels, but adding end-to-end security for those GRASP messages. See . ACP provides for secure, resilient zero-touch discovery of EST servers for certificate renewal. See . ACP provides extensible, auto-configuring hop-by-hop protection of the ACP infrastructure via the negotiation of hop-by-hop secure channel protocols. See . The ACP is designed to minimize attacks from the outside by minimizing its dependency against any non-ACP (Data-Plane) operations/configuration on a node. See also . In combination with BRSKI, ACP enables a resilient, fully zero-touch network solution for short-lived certificates that can be renewed or re-enrolled even after unintentional expiry (e.g., because of interrupted connectivity). See . Because ACP secure channels can be long lived, but certificates used may be short lived, secure channels, for example built via IPsec need to be terminated when peer certificates expire. See . The ACP is designed to minimize attacks from the outside by minimizing its dependency against any non-ACP (Data-Plane) operations/configuration on a node. See also .
This work originated from an Autonomic Networking project at Cisco Systems, which started in early 2010. Many people contributed to this project and the idea of the Autonomic Control Plane, amongst which (in alphabetical order): Ignas Bagdonas, Parag Bhide, Balaji BL, Alex Clemm, Yves Hertoghs, Bruno Klauser, Max Pritikin, Michael Richardson, Ravi Kumar Vadapalli. Special thanks to Brian Carpenter, Elwyn Davies, Joel Halpern and Sheng Jiang for their thorough reviews and to Pascal Thubert and Michael Richardson to provide the details for the recommendations of the use of RPL in the ACP. Thanks to Valery Smyslov for review of the IPsec and IKEv2 configuration parameters. Further input, review or suggestions were received from: Rene Struik, Brian Carpenter, Benoit Claise, William Atwood and Yongkang Zhang.
Only after ACP entered IESG review did it become clear that the in-progress BRSKI document would not provide all the explanations needed for ACP registrars as expected earlier by ACP authors. Instead, BRSKI will only specify a subset of required ACP behavior related to certificate handling and registrar. There, it became clear that the ACP draft should specify generic ACP registrar behavior independent of BRSKI so ACP could be implemented with or without BRSKI and any manual/proprietary or future standardized BRSKI alternatives (for example via NetConf) would understand the requirements for ACP registrars and its certificate handling. This lead to additional text about ACP registrars in the ACP document: 1. Defined relationship ACP / ANI (ANI = ACP + BRSKI). 6.1.4 (new) Overview of trust points and trust anchors required for ACP. Added explanations/requirements for Re-enrolment. 6.10.7 Normative requirements for ACP registrars (BRSKI or not). 10.2 Operational expectations against ACP registrars (BRSKI or not).
There is a wide range of setting up different ACP solution by appropriately using CAs and the domain and rsub elements in the domain information field of the domain certificate. We summarize these options here as they have been explained in different parts of the document in before and discuss possible and desirable extensions: An ACP domain is the set of all ACP nodes using certificates from one or more Trust Anchors (TA) (typically one CA) using the same domain field. GRASP inside the ACP is run across all transitively connected ACP nodes in a domain. The rsub element in the domain information field permits the use of addresses from different ULA prefixes. One use case is to create multiple physical networks that initially may be separated with one ACP domain but different routing subdomains, so that all nodes can mutual trust their ACP domain certificates (not depending on rsub) and so that they could connect later together into a contiguous ACP network. One instance of such a use case is an ACP for regions interconnected via a non-ACP enabled core, for example due to the absence of product support for ACP on the core nodes. ACP connect configurations as defined in this document can be used to extend and interconnect those ACP islands to the NOC and merge them into a single ACP when later that product support gap is closed. Note that RPL scales very well. It is not necessary to use multiple routing subdomains to scale ACP domains in a way it would be possible if other routing protocols where used. They exist only as options for the above mentioned reasons. If different ACP domains are to be created that should not allow to connect to each other by default, these ACP domains simply need to have different domain elements in the domain information field. These domain elements can be arbitrary, including subdomains of one another: Domains "" and "" are separate domains if both are domain elements in the domain information element of certificates. It is not necessary to have a separate CA for different ACP domains: an operator can use a single CA to sign certificates for multiple ACP domains that are not allowed to connect to each other because the checks for ACP adjacencies includes comparison of the domain part. If multiple independent networks choose the same domain name but had their own CA, these would not form a single ACP domain because of CA mismatch. Therefore there is no problem in choosing domain names that are potentially also used by others. Nevertheless it is highly recommended to use domain names that one can have high probability to be unique. It is recommended to use domain names that start with a DNS domain names owned by the assigning organization and unique within it. For example "" if you own "".
..... USA ...... ..... Europe ...... NOC1 NOC2 | | | metric 100 | ACP1 --------------------------- ACP2 . | | . WAN | metric 10 metric 20 | . Core | | . ACP3 --------------------------- ACP4 . | metric 100 | | | . | | . Sites ACP10 ACP11 .
describes diagnostics options that can be done without changing the external, interoperability affecting characteristics of ACP implementations. Even better diagnostics of ACP operations is possible with additional signaling extensions, such as: Consider if LLDP should be a recommended functionality for ANI devices to improve diagnostics, and if so, which information elements it should signal (noting that such information is conveyed in an insecure manner). Includes potentially new information elements. In alternative to LLDP, A DULL GRASP diagnostics objective could be defined to carry these information elements. The IDevID of BRSKI pledges should be included in the selected insecure diagnostics option. This may be undesirable when exposure of device information is seen as too much of a security issue (ability to deduce possible attack vectors from device model for example). A richer set of diagnostics information should be made available via the secured ACP channels, using either single-hop GRASP or network wide "topology discovery" mechanisms.