On May 31, 2012, at 7:26 AM, Nick Hilliard <nick@foobar.org> wrote:
There are many useful ways to build a multi-exit discrimination policy. Using origin is not one of them, in my opinion.
The problem is that origin is ranked one place higher than MED. So if you don't rewrite it, you are automatically giving your upstreams an inherent means of strongly influencing the tie-breaking policy. If this were an attribute which actually meant something, then maybe there would be some point in paying attention to it, but it conveys no useful information these days. IOW, it is completely pointless these days and you almost certainly want to work the possibility of any upstream tweaking it.
Nick
I disagree. Origin is tremendously useful as a multi-AS weighting tool, and isn't the blunt hammer that AS_PATH is. The place where I've gotten the most benefit is large internal networks, where there may be multiple MPLS clouds along with sites cascaded off of them - it provides a way of sending "soft" preferences down the transitive chain. Also useful is "set origin egp XX" - on a route injector, that can post-pend an ASN and limit the spread of a route while still allowing the same transitive properties. David Barak Sent from a mobile device, please forgive autocorrection.