Browsing articles in "Tutorial"
Speed up your console

Generally to upgrade/downgrade an IOS, you use the classical ftp/tftp transfer from a laptop to a router/switch; unfortunately, there are some cases where this way is not possible, so the only solution is to use the console. Suppose you have to upload an image of about 20Mb. On a 9600bps intereface, the time required to upload this image is about 35minutes (20000000/9600)! Oh my God! Fortunately Cisco permit to change the console speed using the command “speed”. By default the console interface works at 9600bps: Ciscozine#sh line console 0 Tty Line Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int […]

Dual Internet connections in active/standby mode without BGP

Suppose that your company has two independent Internet connections: the first used as main link and the second used ONLY in case of main connection fault. What can we do to avoid a ‘manual’ switch of routing and NAT tables? In general, in this case, the best solution is to use the BGP protocol with bofh providers, but this solution can be very expensive, so are there other ways to implement this process? In my opinion, one of the best solutions is to use IPSLA, PBR and the EEM features togheter, but what are these features? See you below each […]

Show interface in depth

In my opinion, a good network engineer must know the “show interface” in depth; indeed, this command is useful to obtain various interface information like drop, duplex mismatch, error, tx/rx load, … Usually, the IOS switch/router have similar “show interface” output; the differences are dictated by devices, interface and IOS. Below a show interface of a TenGigabitEthernet interface. The show is issued on a Cisco WS-C6509-E in VSS Mode with IOS version 15.

How to save configurations using SNMP

Everyone knows there are software to get the configuration using SNMP; but how can you copy the configuration if you don’t have any tool? Let me explain what is SNMP before show you how to implement it. Simple Network Management Protocol (SNMP) is an “Internet-standard protocol for managing devices on IP networks”. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more. It is used mostly in network management systems to monitor network-attached devices for conditions that warrant administrative attention. SNMP uses an extensible design, where the available information is defined by management information bases (MIBs). MIBs describe the […]

Reload in X? Why don’t you rollback or replace the configuration?

Do you remember the article ‘How to schedule a reload‘? This feature (reload in ‘x’) is useful when you must apply a critical configuration on a remote device, for instance new route or new acl. In fact, if you happen to lose connection to device after a change, you must wait the device reload to reconnect to it. This can be a solution but there is a better solution: the replace/roolback feature. Introduced in 12.3(7)T IOS, the Configuration Replace and Configuration Rollback features provide the capability to replace the current running configuration with any saved Cisco IOS configuration file. This […]

Using IP SLA to change routing

Cisco IP SLAs is a part of Cisco IOS that allows Cisco customers to analyze IP service levels for IP applications and services by using active traffic monitoring for measuring network performance. With Cisco IOS IP SLAs, service provider customers can measure and provide service level agreements, and enterprise customers can verify service levels, verify outsourced service level agreements, and understand network performance. Cisco IOS IP SLAs can perform network assessments, verify quality of service (QoS), ease the deployment of new services, and assist with network troubleshooting. IP SLAs collects a unique subset of these performance metrics: Delay (both round-trip […]

PBR: Route a packet based on source IP address

Everyone knows that the routing table lists the routes to particular network destinations, but is it possible define the next-hop based on source ip, packet size or other criteria? Obviously yes! Policy-based routing (PBR) provides a tool for forwarding and routing data packets based on policies defined by network administrators. In effect, it is a way to have the policy override routing protocol decisions. Policy-based routing includes a mechanism for selectively applying policies based on access list, packet size or other criteria. The actions taken can include routing packets on user-defined routes, setting the precedence, type of service bits, etc.

NAT Virtual Interface aka NVI, what is that?!

Not everyone knows that from IOS version 12.3(14)T, Cisco has introduced a new feature called NAT Virtual Interface; NVI removes the requirements to configure an interface as either NAT inside or NAT outside. An interface can be configured to use NAT or not use NAT. How to use NVI? It’s easy! You must use the command ‘ip nat source …’ without specifying the inside/outside tag and enable the nat to the interfaces using the command ‘ip nat enable’. For instance, if you use legacy statement:

Using route maps for conditional NAT

As explained in a previous article, NAT is the process of modifying IP address information in IP packet headers, while route maps are mainly used to redistribute and manipulate routes (OSPF, BGP, EIGRP, and so on). The question is obvious… What is the relationship between these two features? Static NAT configuration with the route-map option can be used to implement destination-based NAT scenarios where the same inside local address needs to be translated to more than one inside global address, depending on where the traffic is destined.

NAT and PAT: a complete explanation

Network address translation (NAT) is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device. There are two different types of NAT: NAT Static NAT: The simplest type of NAT provides a one-to-one translation of IP addresses. It is often also referred to as one-to-one NAT. In this type of NAT only the IP addresses, IP header checksum and any higher level checksums that include the IP address need to be changed. The rest of the packet can be left untouched (at least for basic TCP/UDP functionality, some higher level protocols may […]