Multi site BGP Routing design

Saqib Ilyas msaqib at
Sat Jun 6 12:21:29 UTC 2009

For a given interconnection between the upstream ISPs for the two site, once
the direct link goes down, the time required for site A to learn the new
route to site B and vice versa would be different with the different
proposed solutions, right?
Thanks and best regards

On Sat, Jun 6, 2009 at 12:40 PM, Ivan Pepelnjak <ip at> wrote:

> > To rephrase the OP's question, would it be BCP to acquire a
> > second ASN, and without further de-aggregating, continue
> > advertising each site's IP space to the DFZ, but from
> > dissimilar ASs as opposed to the same one?
> This would definitely be the best approach. You're not introducing new IP
> prefixes and you're not extending AS paths, so the net effect on the global
> BGP routing is zero (OK, you might have to use the 4 byte AS number :).
> Just make sure that both ISPs you connect to allow you to advertise
> "transit" prefixes. If site A public link goes down, but the private link
> is
> up, site B will advertise its own address space plus site A's address space
> with an extra AS number in the AS path (and the upstream ISP might filter
> that).
> Ivan

Muhammad Saqib Ilyas
PhD Student, Computer Science and Engineering
Lahore University of Management Sciences

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