The MPLS WG Archive

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

Narendra Byrapuram wrote:
> 
> How Egress ATM-LSR/FR-LSR distinguishes IPv4 and IPv6 packets?
> 
> In the case of Generic Label, RFC 3032 "MPLS Label Stack Encoding"
> specifies IPv4 Explicit NULL (0) and IPv6 Explicit NULL (2).
> 
> RFC3034 (MPLS on FR) and RFC 3035 (MPLS using ATM VC Switching) doesn't
> talk about the similarly to identify Network Layer.
> 
> When Egress ATM-LSR receives an MPLS packet, how it can identify the packet
> is IPv4 packet or IPv6?
> 
> Could some one point me to the document/rfc where I can find the answer?

I don't think you can tell, just by looking at the data-plane packets.

But you can tell from signaling.  If RSVP-TE is used to set up the LSP, 
the L3PID field in the LABEL_REQUEST object should contan the ethertype 
for IPv4 (0x0800) or IPv6 (0x86dd)

For LDP, I'm not certain, but I would assume that labels that correspond 
to an IPv4 FEC would contain IPv4 payload, and labels correspoding to an 
IPv6 FEC would contain IPv6 payload.

-- David