Network Ninja

Scalability in EIGRP comes from Summarization. In EIGRP Summarization limits advertisements, minimizes the size and optimizes the speed of the routing table, limits route recalculation, and keeps to a minimum the amount of memory and processor resources consumed.

Summarization also solves a unique problem in EIGRP known as query scoping. This is when queries do not stop until they reach a dead-end; because of this, queries can loop. Routing convergence cannot proceed until all queries sent out have a reply. Summarization limits queries by stating “only these routes are found past this point” in effect making dead-ends. Summarization at logical points of the network is important to prevent SIA.

As of IOS 12.2(8) auto summarization happens at the classful network boundaries. This is EIGRP being helpful, however most networks use the private address classes 10.0.0.0/8 or 192.168.x.0/24. But some networks combine the two network-numbers and in that case automatic summarization will need to be disabled.

To disable auto summarization do the following:

Router(config)#router eigrp autonomous-system-number
Router(config-router)#network network-number
Router(config-router)#no auto-summary

Used in an example:

Router(config)#router eigrp 1
Router(config-router)#network 10.0.0.0
Router(config-router)#no auto-summary

From here Summarization may be applied at any point in the network. You can configure manual summarization on any router interface. Summarization for upstream should receive consolidated routes and downstream should receive the default route.

Router(config)#router eigrp autonomous-system-number
Router(config-router)#network network-number
Router(config-router)#no auto-summary
Router(config-router)#exit
Router(config)#interface fastethernet 0/1
Router(config-if)#ip summary-address eigrp autonomous-system-number address mask

Used in an Example:

Router(config)#router eigrp 1
Router(config-router)#network 10.0.0.0
Router(config-router)#no auto-summary
Router(config-router)#exit
!Downstream
Router(config)#interface fastethernet 0/1
Router(config-if)#ip summary-address eigrp 1 0.0.0.0 0.0.0.0
Router(config-if)#exit
!Upstream
Router(config)#interface fastethernet 0/2
Router(config-if)#ip summary-address eigrp 1 10.0.0.0 255.255.255.0
Router(config-if)#exit

Summarizing a default route is useful but where there are multiple default paths, this will reduce routing options and prevent failover when the primary route fails.

Software Study Resources:

The Command Memorizer was originally developed by a CCIE Candidate (David Bombal) for his own use and is now available to anyone who wants to use it.Command Memorizer helped him pass the CCIE Lab on the first attempt, and although I am not a CCIE candidate “officially” I have fiddling with it and finding it useful to test my command line retention and overall progress towards CCIE readiness as I do my current CCNP. The proof will be in the pudding as the Command Memorizer boasts 1000s of commands and hundreds of scenarios to test command line knowledge and retention. It has a section for EIGRP and I also like knowing where I am on my long road to Cisco. Like most study aids / study tools this tool / aid has a specific focus. The Command Memorizer only works when used in conjunction with theoretical backing because you need to know what a command does and how it relates to the technology area. IOW You need to make the connection before you can start drilling actual commands repetitively to get them to start flowing and become second nature. For a disclosure statement on my relationship with Configure Terminal.

Cisco Press Resources:

Stewart, B,D., Gough, C (2008). CCNP BSCI Official Exam Certification Guide, Fourth Edition. Indianapolis: Cisco Press.

Notes and Notices:

This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.