Subject: TTL processing in Ethernet Pseudowire

From: [email-masked]
Date: Wed, 04 Dec 2002 13:38:39 +0100

Hi all,
An Ethernet Pseudowire (PW) allows Ethernet frames to be carried over MPLS.
In this scenario, Ethernet frames entering the MPLS network should be 
encapsulated with a stack of 2 labels: the top label being the one 
transporting the packet to the end of the network; the bottom label 
being the VC label identifying the flow.
I have the following questions regarding TTL values:

1) The obsolete draft-martini-l2circuit-encap-mpls-04 states:
    "The ingress LSR, R1, SHOULD set the TTL field of the VC label to a
     value of 2."
     Is this still valid?

2) What should the TTL be for the outer label?
     Where is it inferred from?

3) How does the outer TTL have to be processed in the core nodes?
     Should it be decremented at every node?
     Can it be decremented only by 1, seeing the entire MPLS network as 
a single hop?

Thanks for your help.
Regards Roberto