Peer templates in Cisco IOS

By andy
Published on April 17th, 2007

When you peer with lots of neighbors (as you should!) your bgp config in IOS is normally one of two things

Ok, so those are the opposite examples, but they don’t sit beyond the realms of possibility. I don’t like peer-groups because I don’t think they’re all that readable, and they are also not so scalable.

In steps the new way:peer templates. These are wonderful and allow you to put together a cascading peering policy for your routers. Templates support inheritance, so I can define in my router a global peering policy that I want every peer to have, and also a transit neighbor policy. Then you can define a template for each of your peered networks which inherits the global rules. Then the neighbor statement inherits the correct template for their AS.

In effect, you have global rules –> rules for a subset of networks –> rules for an AS –> a neighbor command.

To show the template system in action, this is what a peering session with the Cymru route-servers looks like using templates

router bgp 12345
template peer-session bogon-rs
remote-as 65333
description Peering with Team Cymru Bogons rs
password 7 094E176fakepassword271F
ebgp-multihop 255
exit-peer-session
!
no synchronization
bgp log-neighbor-changes
neighbor 194.109.21.101 inherit peer-session bogon-rs
neighbor 194.109.21.101 route-map CYMRUBOGONS in
neighbor 195.214.201.38 inherit peer-session bogon-rs
neighbor 195.214.201.38 route-map CYMRUBOGONS in
Global rules for the AS can be defined in just one place, so if I wanted to vary the max-prefix for an AS at every point where we meet, there is only one place to change the config. To use inheritance in the template peer-session section, use ‘inherit peer-session parent’ inside the ‘template peer-session’ section.

No more ugly, hard to read peer-groups.


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