Subject: [mpls] draft-ietf-mpls-lsp-ping-06.txt

From: Fugui Wang <[email-masked]>
Date: Mon, 30 Aug 2004 13:20:36 -0700 (PDT)

Hello Kireeti and George,

In draft-ietf-mpls-lsp-ping-06.txt page 20, there is a
paragraph saying:

"In "traceroute" mode (fault isolation mode), the TTL
is set successively to 1, 2, ..."

Transit node is suppose to send an Echo Reply
message back with Downstream Mapping object(s).
However, I am just wondering: when the transit node
receives an MPLS packet with TTL expiration, how would
it know the MPLS payload (Echo Request in this case)
is an IP packet(In general, payload could be IPv4,
IPv6, Martini, etc)? If transit node does not know the
MPLS payload, how could it assume that it is an IP/UDP
packet and parse it as an Echo Request? 

Thanks,
Fugui

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