The MPLS WG Archive

[neil.2.harrison@bt.com]

David Charlap wrote18 April 2002 16:33
> 
> Markus Jork wrote:
> > 
> > It looks to me as if the L3PID signaling seemed like a good idea at
> > the time but turned out to be not particularly useful. The problem
> > is that it is often unknown what type of traffic is carried on an
> > LSP.  For example an RSVP LSP can be used to carry IP traffic and
> > at the same time also labeled traffic from a targeted LDP session
> > that runs over the RSVP LSP.
> 
> The L3PID of the inner LSP is known, because it is signaled as IP.
> 
> The ingress router for the inner LSP also knows the L3PID of the outer
> LSP, since it must participate in the signaling for the outer LSP.
> 
> I would argue that it should not shunt incompatible traffic into that
> LSP.  Don't allow a non-IP LSP to tunnel through an IP-LSP.
> 
> If the inner LSP is meant to carry traffic of many different 
> types, then
> it should be signaled as such.  With an L3PID meaning 
> "unknown".  Which
> would mean, of course, that the egress of such an LSP would 
> not be able
> to handle a packet that only has one label - since it won't know the
> actual L3PID after popping that last label.  But this would be OK, if
> there's another label on the stack - either indicating an outer LSP to
> use for forwarding, or indicating the L2/L3 PID.
> 
> Of course, the whole argument falls apart when you realize 
> that the two
> LSPs (inner and outer) don't both have to be RSVP.  I don't 
> think L3PID
> is signaled with LDP or CR-LDP.
NH=> Can I just check something here David.....in the martini-trans ID I
believe only LDP is allowed for signalling XoverMPLS LSPs.  If so, then how
can we signal the payload 'X' of the LSP for such XoverMPLS cases?  I always
assumed that the 'multiprotocol' aspects would be taken care of by label
semantics in lieu of no PID field in the MPLS header.  So am I right one
cannot signal this and only configure it?  And why is RSVP-TE say prohibited
for the setting up the inner LSP?  Any enlightenment/corrections would be
much appreciated.

regards, Neil