[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

Curtis,

No where in the add-paths document, at least the -05 version does it
say anything like that.  The only mention of the decision precoes is


Doesnt say what? That add-paths is used to advertise additional routes
in addition to the best ones?

 7. Applications

  The BGP extension specified in this document can be used by a BGP
  route reflector [RFC2796] or BGP Confederation ASBR [RFC3065] to
  advertise more than just the best path in order to eliminate


"advertise more than just the best path in order to eliminate".

Thus your claim that these proposals only call for advertising the
best routes (ecmp) goes for a toss.

I hope you now appreciate the question that i had earlier asked?

  persistent route oscillations [RFC3345], or to help achieve optimal
  routing in a network.

  Other applications are for further study.

RFC3345 may provide a hint in that the route oscillation cases involve
the decision tie break using MED.  It is possible that the authors
expected the reader to be familiar with this references and in this
case recognize that advertising routes where MED break the tie would
be sufficient to stop the oscillation.

If this was the authors intent, which it may or may not be, then it 

Yes, this was the intent, which i thought was obvious to everyone
involved in this discussion.

Clearly I was mistaken.

Again, I just read the drafts.  I'm not connected with either set of
authors.  Maybe a discussion of the problem space is needed.  I had
considered the BGP ECMP case.  Apparently the primary focus of


If you had considered the ECMP case, then you couldnt have been any
further from reality. Did it ever cross your mind as to how these
proposals would convey the path information to the non
add-paths/multiple-hop peer?

add-path is suppressing RR and confed oscillations.  In private email
Joel pointed out that an RS is a case where a router might want to
send everything without running a decision process at all.


I think Joel's been quite clear on what he means by "everything".


> If the drafts are _only_ meant for ecmp then i see no text that talks
> of how these proposals work with non add-paths/multiple_hops capable
> peers.
>
> Read ecmp-routes-in-bgp draft if you want to understand my point. The
> instant you cross an ECMP domain you have to construct a "synthetic"
> (I picked up this term from this draft) aspath that contains all the
> AS numbers.
>
> Glen

That draft appears to have expired.  There is nothing with ecmp in the
filename, title, or abstract in the internet-drafts abstracts file
except one by George Swallow about MPLS ECMP.


I get this from the first google hit. The expired copy can be found at

http://tools.ietf.org/id/draft-bhatia-ecmp-routes-in-bgp-02.txt

The draft is very specific to their multiple-hop solution but the
basic idea is generic and can be extended to any proposal that
advertises ecmp routes.

From the draft: 

3. Requirements for the ECMP algorithm

  (a)  An ECMP capable peer must be able to advertise each individual
       BGP path to other ECMP capable IBGP peers.

  (b)  When advertising routes to non ECMP capable peers it must
       preserve as much of the AS Path structure as possible. This
       includes, the individual AS elements and the path length.

  We in this document propose an algorithm to advertise BGP ECMP
  routes, to both routers capable of ECMP and the ones without, so as
  to honor each of the requirements mentioned above.

Glen.

_______________________________________________
Idr mailing list
Idr at ietf.org
https://www1.ietf.org/mailman/listinfo/idr