Multi site BGP Routing design

John.Herbert at John.Herbert at
Sat Jun 6 00:35:00 UTC 2009

Depending on your security policies you may want to encrypt said tunnel also.

Other than that, it all depends on it all depends. For example - if you receive / or have a default route pointing to the ISP, then the fact you have the same AS and won't receive the other site's routes in BGP doesn't matter at all - you'll follow a default from site 1 to the ISP, and the ISP will have a route to site 2 and can pass the traffic in the right direction. If you don't mind your traffic being passed unencrypted over the Internet, that is. You'll obviously need to adapt your firewall policies to allow for that flow as well.


From: Chris Adams [cmadams at]
Sent: Friday, June 05, 2009 20:16
To: nanog at
Subject: Re: Multi site BGP Routing design

Once upon a time, Steve Bertrand <steve at> said:
> Unless someone else has any better advice (I'm sure they do), you will
> need two separate public ASNs. Site 1 advertises it's space out of AS1,
> and site 2 advertises it's space from AS2.

I don't know that it's better advice, but another way to link the two
sites is via a tunnel (GRE or IPIP).  Use the upstream IP on each router
as the local endpoint, and then run some routing protocol over the
Chris Adams <cmadams at>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.

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