On 05/31/2012 07:06 PM, Saku Ytti wrote: > On (2012-05-31 08:46 -0700), David Barak wrote: > >> On what precisely do you base the idea that a mandatory transitive attribute >> of a BGP prefix is a "purely advisory flag which has no real meaning"? I >> encourage you to reconsider that opinion - it's actually a useful attribute, >> much the way that MED is a useful attribute. Many providers re-write MED, >> and apparently some re-write ORIGIN. Neither of those is "network abuse" - >> it's more accurately described as "network routing policy." As has been >> stated here before: your network, your rules. > > When provider rewrites MED, they do it, because they don't want peer to > cause them to cold-potato, to which they may have compelling reason. > Then some clever people realise they forgot to rewrite origin, working > around the implicit agreement you had with them. >
You CAN rewrite MED, as stated in RFC 4271, section 5.1.4 - but you SHOULD NOT change origin attribute, as stated in section 5.1.1. So, in terms of rewriting, MED is not comparable to origin. I think RFC 4271 (http://tools.ietf.org/html/rfc4271) is very clear here. Back to the standard, why condone it's violation? Yes, statement about origin is here since January 2006 - older RFC 1771 didn't contain similar rule. But 6 years after publishing I think everyone had enough time to implement this correctly. I still think, that professionals shoult follow RFC and not insert their own creativity to places, where's not expected - just because they decide that as a "cool" idea. For local routing policy - there're still lot of knobs, which can be used internally (typically MED, LOCPREF) to enforce expected policy and there's technically no reason to change origin. -- Daniel