The MPLS WG Archive

[Bora Akyol <akyol@pluris.com>]

For MPLS based VPNs, LDP scales better than RSVP-TE and requires less
configuration as the network evolves.

What happens is that egress routers advertise /32 FECs to themselves in
Downstream-Unsolicited mode with liberal label retention. iBGP with
"advertise-self" is used to set the NH attribute to the iBGP peer instead
of the eBGP peer. This allows two things:

1) Only transit traffic gets sucked into the tunnels. This is what VPNs
are about.

2) Core routers in the network know nothing about the BGP peering and they
don't run BGP.

As an added benefit, with liberal retention, LDP is able to heal much
faster when routers in the middle of the network become unreachable.

Makes sense?

Bora
Who thinks that someone should write a BCP on MPLS based VPN usage.


On Wed, 11 Apr 2001, HANSEN CHAN wrote:

> Eric,
>
> Then mind telling us what are the reasons? I have been hearing LDP is used to
> achieve maximum degree of interoperability with other vendors. However, I find
> it difficult to accept as there're probably much more vendors supporting RSVP-TE
> than LDP.
>
> Cheers,
> Hansen
>
> Eric Rosen wrote:
>
> > Curtis> My understanding of the real reason  why we are using LDP for VPN is
> > Curtis> that it had more to do  with the scalability of a particular RSVP/TE
> > Curtis> implementation
> >
> > If you are speculating about the reason Cisco uses LDP in support of RFC2547
> > VPNs, then I  can state authoritatively that this  has nothing whatsoever to
> > do with any characteristic of any RSVP/TE implementation.
>