Multi site BGP Routing design

John.Herbert at John.Herbert at
Sat Jun 6 00:40:15 UTC 2009

This is a good concept but if the ISP route is a Juniper then as I recall by default it looks ahead, sees the as-path routing loop if it were to send it to the other router, and doesn't send it. So while you might be able to configure it on the receiving router, if the sending router won't send it, you're SOL.


From: Chuck Anderson [cra at WPI.EDU]
Sent: Friday, June 05, 2009 20:33
To: nanog at
Subject: Re: Multi site BGP Routing design

On Fri, Jun 05, 2009 at 05:50:28PM -0500, Justin Krejci wrote:
> If the private link between the two sites fails, will BGP allow for us to
> access the IP subnets at site 2 from site 1 via the internet given that both
> sites are advertising under the same ASN?

Maybe.  Especially if both sites are connected to the same ISP, you
can tweak some BGP knobs to allow your own ASN to appear in the AS
PATH N times where N > 1, and accept the routes anyway.

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