From: Chad Hintz (ccie_2b2004@yahoo.com)
Date: Sat Dec 31 2005 - 10:30:39 GMT-3
Mike,
From my understanding if you are asked for confederations the first solution would be correct. The local as command is used for transitioning from one AS to another without breaking existing peering relationships. What I mean by that is if your company owned as1 and bought a company with as2, then for as2 router to peer via ibgp to as1 router the would be configured with router bgp 1, but using the local as gives them the ability to still peer with neighbors they had before they were purchased by as1 by issuing the neighbor X..X.X.X LOCAL-AS 2.
Here is a link from cisco's website that explains it better.
http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800949cd.shtml#backinfo
Confederation are used to break up your internal AS into smaller sub AS's to help with the amount of peers and the ability to break up administrative groups. It also helps with the issues related to ibgp from a route propagation perspective and the need for a route reflector is some cases.
HTH,
Chad
Michael Brooks <michaeljbrooks@gmail.com> wrote:
I need some clarification in regards to a router in a BGP confederation
forming an ebgp peering relationship.
R1 (AS: 100/Confed AS 65026) <----> ISP-R2 (AS 200)
On R1 would you configure:
R1:
router bgp 65026
neighbor 1.1.1.2 remote-as 200 (isp)
*bgp confederation identifier 100*
***OR****
R1:
router bgp 65026
neighbor 1.1.1.2 remote-as 200 (isp)
*neighbor 1.1.1.2 local-as 100
*
**********************
Both configurations appear to work, but I am curious to know what the
preferred method is and why ? Also, I noticed the "local-as" command takes
precedence over the "confederation identifier" command when both configured
at the same time. Are these commands basically inter-changeable when
configuring ebgp peering relationships (besides the identification of the
neighbor with local-as command). Your input would be greatly aprreciated.
Thanks,
Mike
This archive was generated by hypermail 2.1.4 : Mon Jan 09 2006 - 07:07:52 GMT-3