Subject: CR-LDP indicator for network layer protocol

From: Nick Weeds <[email-masked]>
Date: Tue, 16 Nov 1999 14:22:10 -0000

Bilel,

As far as I can see, the CR-LDP Label Request messages doesn't carry an
indicator of the network layer protocol to be carried on the LSP tunnel
being set up.  Is this deliberate?

Background:

*	draft-ietf-mpls-label-encaps-07.txt section 2.2 discusses the need
to determine the network layer protocol for labeled packets, and also
discusses the problem of determining the network layer protocol.  The
general intent is to infer the the network layer protocol from the top
label:
"... the identity of the network layer protocol must be inferable from the
value of the label which is popped from the bottom of the stack,  possibly
along with the contents of the network layer header itself."
To avoid guessing, the LSP setup protocol must carry the network layer
protocol to be carried on the LSP.

*	RSVP includes the network layer protocol (ethertype) in the
LABEL_REQUEST object.

*	LDP implicitly includes the network layer protocol in the FEC TLV
because the FEC element contains the address family (and address families
are closely related to protocols).

*	CR-LDP doesn't include the address family in the CR-LDP FEC TLV, and
doesn't appear to have an alternative mechanism for indicating the network
layer protocol.

Thus it appears the LSRs are left to guess the network layer protocol for
any packet received on an LSP tunnel set up using CR-LDP.

This isn't a problem if we restrict ourselves to IPv4.  With IPv4 and IPv6
it's easy to distinguish the protocol by looking at the IP header.  
However, if other protocols are carried in future then protocol guessing
might be difficult, so it would still be desirable to carry the network
layer protocol id in the CR-LDP Label Request message.

What do you think?  Do you think we should retain a network layer protocol
identifier in the CR-LDP FEC TLV?

Thanks,

	Nick.

> Nick Weeds
> Software Developer
> Data Connection Ltd
> Tel:	+44 1244 313440		Fax:	+44 1244 312422
> Email:	[email-masked]		Web:
> http://www.datcon.co.uk
>