Re: FW: I-D ACTION:draft-bhatia-ecmp-routes-in-bgp-00.txt

[Manav Bhatia <[e-mail]>]

Mareline,
The design implicitly takes care of the scenario you explain.  Though I
confess that I have not been really clear on this in this version of the
draft.

To advertise two ECMP routes with different attributes we will use two
UPDATEs where each will be sent with a blank ECMP_NEXT_HOP attribute (nos.
of next-hops will be kept as zero). The receiver upon receiving such
UPDATEs will know that since the ECMP_NEXT_HOP attribute is present in the
UPDATE, it needs to be added in addition to what it has already.

I guess the following text needs to be added in the draft.

The receiver SHOULD not remove any previous route and add the route
received with an ECMP_NEXT_HOP attribute rather than replace the previous
routes.

When advertising more than one ECMP hop with identical attributes the
sender SHOULD send a single update with multiple hops listed in the
ECMP_NEXT_HOP attribute.

When advertising more than one ECMP hop which do not have identical
attributes multiple BGP updates MUST be sent with the ECMP_NEXT_HOP
attribute included to suppress route replacement.

But a more important question is that whether we need this kind of
mechanism in BGP or not. We already have multiple drafts proposed which
strive to achieve similar goals using different techniques and mechanisms.
I guess one motivation being, to allow inter-operatibility between
different vendors to allow advertisement of multiple BGP paths of same
preference.

Once we're through with the above discussion, we can sit down and look into
the nitty-gritties of each proposal.

Regards,
Manav



----- Original Message ----- 
From: "Mareline Sheldon" <[e-mail]>
To: "Manav Bhatia" <[e-mail]>
Cc: <[e-mail]>
Sent: Sunday, May 18, 2003 9:54 AM
Subject: Re: FW: I-D ACTION:draft-bhatia-ecmp-routes-in-bgp-00.txt


> Manav,
> Can we using this draft advertise two ECMP routes of equal preference but
say, with different
> AS Paths. As far as i could gather you use one additional attribute to
describe equal cost
> routes using the same path attributes. This way you can definitely
advertise routes with all
> the same attributes. But what happens say when one of my path attributes
are different. Eg. AS
> PATH 112 123 in one attribute and AS PATH 564 232 in the other?
>
> Can this be done here?
>
> Regards,
> Mareline S.
>
> --- Manav Bhatia <[e-mail]> wrote:
> > Hi,
> > Please look into this new Internet draft which is available from the
> > on-line Internet-Drafts directories.
> >
> > I-D ACTION:draft-bhatia-ecmp-routes-in-bgp-00.txt
> > To: IETF-Announce: ;
> > Subject: I-D ACTION:draft-bhatia-ecmp-routes-in-bgp-00.txt
> > From: [e-mail]
> > Date: Thu, 15 May 2003 07:19:32 -0400
> > Reply-to: [e-mail]
> > Sender: [e-mail]
> >
> > A New Internet-Draft is available
> >
> > Title  : Advertising Equal Cost Multi-Path (ECMP) routes in BGP
> > Author(s) : M. Bhatia
> > Filename : draft-bhatia-ecmp-routes-in-bgp-00.txt
> > Pages  : 7
> > Date  : 2003-5-14
> >
> > This document describes an extensible mechanism that will allow a BGP
> > [BGP4] speaker to advertise equal cost multi-path (ECMP) routes for a
> > destination to its peers without changing the semantics of the UPDATE
> > message.
> >
> > A new BGP attribute is introduced that will be used to advertise the
> > multiple next hops for the feasible and the un-feasible ECMP BGP routes
to
> > the remote peers.
> >
> > The mechanisms described in this document are applicable to all
routers,
> > both those with the ability to inject multiple routing  entries in
their
> > forwarding table and those without (although the latter need not
implement
> > some extensions described in this document).
> >
> > A URL for this Internet-Draft is:
> >
http://www.ietf.org/internet-drafts/draft-bhatia-ecmp-routes-in-bgp-00.txt
> >
> >
> > To remove yourself from the IETF Announcement list, send a message to
> > ietf-announce-request with the word unsubscribe in the body of the
message.
> >
> > Internet-Drafts are also available by anonymous FTP. Login with the
> > username "anonymous" and a password of your e-mail address. After
logging
> > in, type "cd internet-drafts" and then
> >  "get draft-bhatia-ecmp-routes-in-bgp-00.txt".
> >
> >
> >
>
>
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