The MPLS WG Archive

[David Charlap <David.Charlap@marconi.com>]

Eric Rosen wrote:
> 
> I  admit I've  never  quite understood  the  role of  the  L3PID in
> RSVP-TE signaling.

It's so the egress router will know what to do with the packet after
popping the last label.

If you don't provide this (like LDP doesn't) then you must either assume
everything is IP, or you must use some out-of-band mechanism for
distributing this information.  Either way, it pretty much defeats the
multiprotocol capabilities of MPLS.

> In practice, the only situations in which PHP causes a packet's
> bottom label to be  popped off are  situations in which the payload
> is an "ordinary" IP packet.

Why are you forcing it to be IP?  Why can't people using other L3
protocols also send traffic through LSPs?

> If the payload is a layer 2 frame encapsulated via draft-martini,
> or a VPN packet encapsulated according to one of the L3VPN schemes,
> then PHP will never result in the bottom label being popped off.

There are more non-IP protocols than VPNs.

And why is it so superior to carry the L3 protocol ID in every single
packet, instead of signaling it once when the LSP is established?

-- David