redundant bgp design question with backdoor

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Jul 3rd, 2009
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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?

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milan.kulik Fri, 07/03/2009 - 05:23
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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:



chinkevi_2 Sat, 07/04/2009 - 04:06
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both sites are using the same isp in the same vpn. AS are private.

Joseph W. Doherty Sun, 07/05/2009 - 19:43
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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.


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