The MPLS-OPS Archive

["Jim Guichard" <jguichar@cisco.com>]

Hi Yakov,

ok, so maybe I have one more point :)

> >-----Original Message-----
> >From: Yakov Rekhter [mailto:yakov@juniper.net]
> >Sent: Thursday, May 16, 2002 9:13 AM
> >To: Jim Guichard
> >Cc: mpls-ops@mplsrc.com
> >Subject: Re: [MPLS-OPS]: Fwd: Re: Why martini over kompella
> >
> >
> >Jim,
> >
> >> One point to add below ..
> >
> >likewise, I have one point to add as well :-)
> >
> >[clipped...]
> >
> >> > >>So, why BGP instead of LDP?  BGP does auto-discovery; LDP doesn't.
> >> > >>This makes a huge difference to the task of provisioning VPNs.
> >> > >>
> >> > >>BGP is also better suited to building largish VPNs -- with LDP, the
> >> > >>protocol state maintained in the network, the number of
> >targeted LDP
> >> > >>sessions, etc. all get pretty large pretty quickly [O(N**2)].  With
> >> > >>BGP, the protocol state in the network is O(N); and one
> >can use route
> >> > >>reflectors and/or confeds to keep the number of sessions at O(N).
> >> > >>Finally, if one is interested in building inter-AS/inter-provider
> >> > >>VPNs, BGP is a clear winner.
> >>
> >> I do not think that this is comparing apples to apples -
> >directed LDP has to
> >> distribute information to a particular endpoint for a given
> >attachment VC
> >> whereas BGP wants, by default, to distribute the information
> >to everyone. So
> >> although there will be a larger number of directed LDP
> >sessions than BGP
> >> sessions (with RRs), the amount of information that must be
> >carried by the
> >> directed LDP sessions is by no means the same as BGP sessions.
> >This means
> >> that the scaling implications are not the same as with BGP. Jim
> >
> >To avoid distributing the information to everyone one can use BGP
> >Outbound Route Filters (ORFs). And with ORFs the amount of information
> >that one needs to carry over BGP is comparable to the amount of
> >information one would need to carry over the directed LDP session.

I agree that ORF provides some scaling enhancements but my main point was
that if I have say 10 local VCs, these VCs will be bound to a number of
remote PEs. However, only a subset of the VC information needs to be
distributed across each of the attached directed LDP sessions. With BGP, we
must send all the VC information to the RR, unless we adopt some kind of RR
partitioning based on pseudowires so that we are able to adopt the ORF
functionality. Jim

> >

> >Yakov.
> >
> >P.S. For more details on ORF one may look at
> >draft-ietf-idr-route-filter-06.txt.

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