The MPLS WG Archive

["James R. Leu" <jleu@laurelnetworks.com>]

I agree with Eric.

Not only would this provide a means to clearly indicate that the resulting
LSP should utilize (tunnel through) and existing LSP.  It would also align
RSVP-TE, CR-LDP, and the TE-MIB with respect to EROs.

Jim
-- 
James R. Leu
Software Engineer
Laurel Networks, Inc
jleu@laurelnetworks.com

On Wed, Aug 16, 2000 at 09:57:13AM -0700, Eric Gray wrote:
> Kireeti,
> 
> 	Hi.
> 
> 	I'm afraid that this doesn't help, too much,
> in understanding how this might be done.  For one
> thing, if the interface ID sub-object type you've
> defined in the unnumbered draft (I am assuming you
> refer to draft-kompella-mpls-unnum-00) is intended
> to be used to identify LSPs, then it should maybe
> have been defined as a larger than 16-bit field.
> Since LSPs may be extended to large numbers of 
> LSRs either directly or indirectly connected, the
> number of interface IDs needed may be arbitrarily 
> large.
> 
> 	For another, there's an issue with how an LSR
> might interpret an IPv4 prefix in an ERO when there
> are multiple routes to that prefix - including one
> or more that traverse an LSP.  In fact, there is 
> nothing to prevent having more than one LSP at any
> LSR that extends toward an IPv4 prefix, is there?   
> And, although it may make sense to use an LSP that 
> directly connects the current LSR to a remote next 
> hop associated with the IPv4 prefix specified in an 
> ERO, if you cannot explicitly identify the LSP, the 
> local routing engine may decide to use another route.  
> This would appear to defeat the purpose of using the 
> ERO.
> 
> 	So, I guess the question comes down to "is there
> a reason why a user might want to force the path to
> follow a particular LSP even when routing would prefer
> a different path?"  I think the answer is yes, using
> Alan's specific example as a case in point, so the
> next question is - "how do we force this behavior?"
> 
> 	In CR-LDP, there is an explicit LSPID Hop type.
> Perhaps there should be a "Session" sub-object for 
> RSVP-TE?
> 
> 	Thanks!
> 
> > -----Original Message-----
> > From: Kireeti Kompella [mailto:kireeti@juniper.net]
> > Sent: Wednesday, August 16, 2000 9:16 AM
> > To: akullber@netplane.com; mpls@UU.NET
> > Subject: Re: generalized MPLS signaling question
> > 
> > 
> > > how do LSR-A and LSR-B coordinate
> > > the timeslot allocation so that LSR-A sends the data in the
> > > timeslot on the correct Lambda?
> > 
> > Using the ERO.  Each lambda (actually, lambda-switched path) is
> > uniquely identified, either by an IP address or by an "interface"
> > index as defined in the unnumbered draft.
> > 
> > Kireeti.
> >