Section: 11.2.1.3.2 IPv6 Stateless Address Autoconfiguration
Content: As described in 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [3], the IPv6 prefix of a PDP Context of PDP type IPv6 or IPv4v6 activated by means of the IPv6 Stateless Address Autoconfiguration Procedure is uniquely identified by the prefix part of the IPv6 address only. The MS may select any value for the Interface-Identifier part of the address. The only exception is the Interface-Identifier for the link-local address used by the MS (see RFC 4291 [82]). This Interface-Identifier shall be assigned by the GGSN to avoid any conflict between the link-local address of the MS and that of the GGSN itself. This is described in subclause "IPv6 PDP Context Activation" above. For IPv6 the PDP Context Activation phase is followed by an address autoconfiguration phase. The procedure describing APNs configured to use Stateless Address Autoconfiguration, may be as follows: 1) After the first phase of setting up IPv6 access to an Intranet or ISP, the MS shall use the IPv6 Interface-Identifier, as provided by the GGSN, to create its IPv6 Link-Local Unicast Address according to RFC 4291 [82]. Before the MS can communicate with other hosts or Mses on the Intranet/ISP, the MS must obtain an IPv6 Global or Site-Local Unicast Address. The simplest way is the IPv6 Stateless Address Autoconfiguration procedure described below and in 3GPP TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [3]. The procedure is consistent with RFC 4862 [83]. The procedure below takes place through signalling in the user plane. It is done on the link between the MS and the GGSN. From the MS perspective the GGSN is now the first router on the link. 2) After the GGSN has sent a Create PDP Context Response message to the SGSN, it shall start sending Router Advertisements periodically on the new MS-GGSN link established by the PDP Context. The MS may issue a Router Solicitation directly after the user plane establishment. This shall trigger the GGSN to send a Router Advertisement immediately. To indicate to the MS that stateless address autoconfiguration shall be performed, the GGSN shall leave the M-flag cleared in the Router Advertisement messages. The GGSN may set the O-flag if there are additional configuration parameters that need to be fetched by the MS (see below). The Prefix sent in the Router Advertisements shall be identical to the Prefix returned in the Create PDP Context Response. The Prefix is contained in the Prefix Information Option of the Router Advertisements and shall have the A-flag set ("Autonomous address configuration flag") and the L-flag cleared (i.e. the prefix should not be used for on-link determination). The lifetime of the prefix shall be set to infinity. In practice, the lifetime of a Prefix will be the lifetime of its PDP Context. There shall be exactly one Prefix included in the Router Advertisements. The handling of Router Advertisements shall be consistent with what is specified in RFC 4861 [89]. For the MS-GGSN link however, some specific handling shall apply. The randomisation part to determine when Router Advertisements shall be sent may be omitted since the GGSN is the only router on the link. Furthermore, some 3GPP specific protocol constants and default values shall apply (see subclause "IPv6 Router Configuration Variables in the GGSN"). These relate to the periodicity of the Router Advertisements initially and during continued operation. The motivation for this is to have a faster user-plane set-up even in bad radio conditions and to minimize MS power consumption during long continued operation. 3) When creating a Global or Site-Local Unicast Address, the MS may use the Interface-Identifier received during the PDP Context Activation phase or it may generate a new Interface-Identifier. There is no restriction on the value of the Interface-Identifier of the Global or Site-Local Unicast Address, since the Prefix is unique. Interface-Identifiers shall in any case be 64-bit long. Since the GGSN guarantees that the Prefix is unique, the MS does not need to perform any Duplicate Address Detection on addresses it creates. That is, the ‘DupAddrDetectTransmits’ variable in the MS should have a value of zero. If the MS finds more than one Prefix in the Router Advertisement message, it shall only consider the first one and silently discard the others. The GGSN shall not generate any globally unique IPv6 addresses for itself using the Prefix assigned to the MS in the Router Advertisement. If the O-flag ("Other configuration flag") was set in the Router Advertisement, the MS may start a DHCP session to retrieve additional configuration parameters. See subclause 13.2.2 "Other configuration by the Intranet or ISP". If the MS is not DHCP capable, the O-flag may be ignored. Figure 11bb: IPv6 Stateless Address Autoconfiguration