Hi Greg,
> > Have anyone tried to document that instead of doing AS-PATH prepend > across set of upstreams (for whatever valid reason that may be) the > preferred entrance should advertise the paths with IGP or EGP origin while > the other ASBRs (which would otherwise prepend N times) with INCOMPLETE ? > BGP best path should automatically across most implementations do the right > path selection. > > Offhand, I don’t know of anyone who has tried to document this. But why > EGP origin? EGP is a Historic protocol that is rarely if ever used. IMO, > although this technique could work, it is misleading. > I thought it is not used too but looking at the BGP table it is there: cto-asr1x-ny1#sh ip bgp detail | count .*EGP.*external, best.* Number of lines which match regexp = 826 cto-asr1x-ny1#sh ip bgp detail | count .*EGP.* Number of lines which match regexp = 2345 Then looking at some vendor's docs I see that they apply it if the advertised route was learned via different ASN (many folks run more then one AS globally) bit of surprise as RFC4271 never mentioned such use case. origin egp—(Optional) BGP origin attribute that indicates that the path information originated in another AS. So one could argue that it is misleading already today :) > If not maybe we should think about a new attribute along the lines of > cost community to be more widely used in a transitive manner and to have > single meaning to allow to deprefer a prefix originated by given AS across > number of ISP uplinks with a numeric value (just like MED or Local Pref are > used locally). > > IMO, this is a better idea. Well sure, but you know the time we take to define it, the time vendors take to implement it, the time it takes to deploy it then the time it takes for folks to actually start using it we are talking years ... Sure if we never start we will never get there but in the mean time perhaps we could use what's deployed everywhere to trim size of AS-PATHs yet get all the benefits of AS-PATH prepends ? Clearly I am here just trying to probe the WG list on three questions ... Is it worth to try it - ie. do we have a problem, Is this a good idea - ie. do we break anything, Should this option be added to draft-mcbride-grow-as-path-prepend as something to consider instead of doing N times AS-PATH prepend (often N > 5 or N> 10 ....) See at the end of the day the best thing about this is that anyone can try to advertise his paths with different origin even today and it should just work - without anyone else doing anything configuration wise in the upstream ASNs. Thx, R.
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