Subject: [mpls] lsp trace route question

From: "Amit Goyal \(agoyal\)" <[email-masked]>
Date: Wed, 2 Feb 2005 09:48:27 +0530

Hi All,

I have a question for lsp trace route in scenario where label stack of depth
n ( n>1) is required to reach the destination. In such cases how many FEC
elements would be there in FEC stack of echo request? If there would be only
one FEC element corresponding to destination (not tunnel end point) then how
does the intermediate LSR makes the FEC to label matching processing
(section 4.3 of draft-ietf-mpls-lsp-ping-70).

I am assuming the intermediate LSR is not aware of the destination FEC.

If the FEC stack contains same number of elements as there are tunnels then
FEC to label matching processing could be done. so is it mandatory in case
of tunnels that the trace route echo request contains all tunnel endpoints
the LSP traverses. While "ping" mode echo request can contain only
destination FEC element as only egress LSR control plane is going to do all
that check.

Another question I have is why the FEC matching is started from bottom of
both the stacks, as intermediate router would not be aware of the bottom
most label and FEC and as per section 4.3 step 3 in this case it would reply
with a return code 4 "Replying router has no mapping for the FEC at
stack-depth"

Thanks in advance

Amit Goyal

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