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@ioshints.info> 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