Re: [Idr] Progressing draft-bhatia-bgp-multiple-next-hops-01.txt

["John G. Scudder" <jgs at cisco.com>]

At 8:44 PM +0100 8/24/06, Paul Jakma wrote:
> On Thu, 24 Aug 2006, Enke Chen wrote:
>
> > Let us give a trivial algorithm:
> >
> > For a prefix, allocate the path identifiers for paths sequentially 
> > starting from 0, do not reuse until it wraps (that will take many 
> > many years).
>
> Now you receive a path update and must pass it on to this peer, how 
> do you find out whether a previous path was advertised?

The referent of "this" isn't clear but I'll take a shot at answering anyway.

> Bear in mind, you can't just compare against peer path was received 
> from, because there can be multiple such paths.

- Peer A sends us route R for prefix P with path ID N.
- If peer A has not previously sent us a route for P with ID N,
  this is a new route.  We store it, allocating it local ID M
  calculated as P->local_id++ (you get the idea I hope).  Now
  that we have a local ID for it, we can advertise it using that
  ID, following whatever normal procedures we have for
  advertising a route to a peer.
- If peer A has previously sent us a route for prefix
  P with path ID N, this is a replacement.  We replace our
  local copy -- there is no need to recompute our local ID as we
  already have one -- and re-advertise the route using our local
  ID, following whatever normal procedures we have for advertising
  a route to a peer.

I'm not sure if that answers your question or not.  If the question 
was "how do you know if the peer previously advertised a route to 
us?" the answer is "you look it up, just like you do now, only 
considering the path ID as well".  If the question was "how do you 
know if you previously advertised the route to your (other) peer?" 
the answer is "just like you do now".  If I've missed the sense of 
your question altogether, please ask again.

--John

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