On May 31, 2012, at 7:26 AM, Nick Hilliard <n...@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.