consistent policy != consistent announcements

John Scudder jgs at
Thu Mar 13 15:46:06 UTC 1997

> Yep, policy filters run up against the policy of only announcing the
> single, best route.  I've been thinking with policy filters and variable
> weighting, should it be changed to announcing the 'best' route that
> meets policy, even if it is the second or third 'best' route you
> know about.

Unless I misunderstand what you mean by "variable weighting", this
would not be a good idea.

It's a BGP design point for a router to only announce the route(s) that
it is actively *using*.  In your comment above,

a. If a router has a route it believes is "best", why isn't it using

b. Regardless of the answer, the router should announce the route it is
   using for its own forwarding.  To do otherwise would be to lie about
   the path which traffic will take to the advertised destination.  

   If policy forbids it from announcing the route it is using, so be
   it.  (Or, if that's not acceptable change the policy.)

By the way, this general fact about BGP (external announcements are
governed by internal route selection) also means that for Randy to
always announce the same route to his peer, he would have to change his
own, internal routing policy to do cold-potato routing to one of the
two candidate paths.  This doesn't seem like a reasonable thing for a
peer to demand he do.



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