BGP maximum-path

Answered Question
Apr 18th, 2007

Dear All,

I required your comments on a scenario of multihoming to a single provider.RouterA have 2 links with upstream provider and using maximum-path command to install more than 1 path in routing table for a prefix learned from both eBGP sessions.RouterA have iBGP session with RouterB also in its AS, now my question is that when I check BGP table for a prefix ( suppose 11.11.0.0 /16 ) at RouterB then it shows next hop ip address of its peer i.e RouterA although I am not using nexthop-self command on RouterA.Is this behaviour is due to maximum-path command ??

Regards,

Mujeeb

I have this problem too.
0 votes
Correct Answer by Harold Ritter about 7 years 6 days ago

Mujeeb,

You are correct. In this scenario, the next-hop-self is set to self by router A because "maximum-paths" is configured and as a result of that multiple BGP paths are installed in the RIB.

Hope this helps,

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Average Rating: 5 (2 ratings)
danail-petrov Wed, 04/18/2007 - 02:31

Hello Mujeeb,

because of iBGP protocol ,the next-hop attribute is the IP address of the iBGP peer. If you setup another iBGP session between routerB and another routerC, the router C will receive announce for this prefix (11.11.0.0/16) with next-hop address of router A. Check this out:

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/bgp.htm#wp1020610

hope that helps!

BR,

Danail Petrov

nedian123 Wed, 04/18/2007 - 03:07

Danail,

Router B would not advertise 11.11.0.0/16(learned from eBGP peers) to RouterC b/c of split horizon. As far as Mujeeb's issue is concerned i also have noticed that RouterB would show next-hop to Router A for prefix 11.11.0.0/16 if & only if maximum path 2 is defined on Router A without using next-hop-self.

Regards,

Akhtar

Correct Answer
Harold Ritter Wed, 04/18/2007 - 04:24

Mujeeb,

You are correct. In this scenario, the next-hop-self is set to self by router A because "maximum-paths" is configured and as a result of that multiple BGP paths are installed in the RIB.

Hope this helps,

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Posted April 18, 2007 at 1:07 AM
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