The MPLS WG Archive

[Curtis Villamizar <curtis@avici.com>]

In message <4.2.2.20000427091619.00a8fd10@farley.cisco.com>, Jeremy Lawrence wr
ites:
> Jim,
> 
> At 05:13 04/27/2000 -0400, Jim Sullivan wrote:
> >Jeremy, 
> >
> >
> >At 06:47 PM 04/26/2000 +1000, Jeremy Lawrence wrote:
> > >At 17:39 04/25/2000 -0700, Bora Akyol wrote:
> 
> [...]
> > >>FEC to LSP binding is almost historical now.
> > >
> > >That's arguably true in router-based networks, because of the
> > >predominance of TE as an application of MPLS in those networks.
> > >However, FEC to LSP binding is very much alive in ATM MPLS
> > >networks. 
> >I'm not sure I completely follow this thread. I make the assumption
> >that Bora believes all packets that do not get forwarded on 
> >TE LSPs can be efficiently forwarded as unlabeled packets. 
> >Is the point your raising that ATM-LSRs in general can not
> >be expected to forward unlabeled traffic efficiently ? 
> 
> Exactly right. ATM-LSRs do not necessarily have any capability
> of forwarding unlabelled packets. Most, but not all, ATM-LSRs 
> have some capacity to forward unlabelled packets, but (in all
> cases I'm aware of) this is limited compared to their capacity
> for labelled packet forwarding.
> 
> So, where the 'default' forwarding mechanism in a router network
> using MPLS TE can sometimes be ordinary IP packet forwarding (see
> also the next paragraph), the default mechanism in an ATM MPLS
> network normally must be hop-by-hop routed MPLS.
> 
> There are also several VPN schemes that require labelled packet
> forwarding as the default in any type of MPLS network over which
> they operate.
> 
> Regards,
> 
> Jeremy Lawrence


Jeremy,

Some ISPs have considered running MPLS-RSVP backbones in which the
interior nodes do run an IGP but do not run IBGP.  In such a network,
any router which has one or more EBGP peers must run IBGP and have a
tunnel to any other router with one or more EBGP peer.  The IGP
carries only internal routes and is used for the MPLS signaling plus
management of the network.

This design does not forward external IP traffic hop by hop and does
not use LDP either.  A similar approach could be taken for MPLS-ATM.

Curtis