redundant bgp design question with backdoor

chinkevi_2 · ‎07-03-2009

lately i'm starting to see networks as such that 2 sites with different BGP AS has backdoor connection between the sites. The preferred routes between the sites are via backdoor link.

The CE on both sites are doing BGP with ISP and IGP on the internal network, so both CE are advertising the same routes to ISP.

controlling routing in this scenario is quite a nightmare. Wouldn't it be better if both sites use the same AS?

so is there a pointer on how this should be done properly?

milan.kulik · ‎07-03-2009

Hi,

IMHO, if you are advertising the same prefixes to both ISPs, you should definitely use the same AS number.

Otherwise, your prefixes will be as-inconsistent in the Internet.

But do you own a public AS number?

If using a private AS number, it will be removed by the ISP anyway.

This might help you:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf5

BR,

Milan

chinkevi_2 · ‎07-04-2009

both sites are using the same isp in the same vpn. AS are private.

chinkevi_2 · ‎07-05-2009

found a similar situation, the discussion have a few suggestion:

http://supportwiki.cisco.com/ViewWiki/index.php?title=Tech_Insights_talk:Preferring_MPLS_VPN_BGP_Path_with_IGP_Backup&edit

Joseph W. Doherty · ‎07-05-2009

Another possible approach . . .

eBGP peer between (AS) sites on the "inside" too. Be "default", one less AS hop so it would be the preferred path between those sites. Basically all your off-site routing becomes BGP.