Subject: [mpls] Questions on draft-ietf-mpls-lsp-ping-enhanced-dsmap-08

From: [email-masked]
Date: Fri, 4 Mar 2011 14:52:02 +0800

Dear authors,

I have some questions on draft-ietf-mpls-lsp-ping-enhanced-dsmap-08.

1. In the specified paragraph following "Remote peer addrss" in Section 
3.3.3, there is an example described as
"E.g.  In the LDP over RSVP case Figure 1, router B would respond back 
with the address of router D as the remote peer address for the LDP FEC 
being traced." 

The Figure 1 mentioned is:
   A           B           C            D            E 
   o -------- o -------- o --------- o --------- o 
     \_____/  | \______/    \______/ | \______/ 
       LDP    |   RSVP        RSVP   |    LDP 
              |                      | 
               \____________________/ 
                         LDP 

According to the usage described in this draft, there is no FEC Stack 
change sub-TLV for the LDP FEC being traced. And, there will be only one 
FEC Stack change sub-TLV, for the RSVP FEC. In this example, does it mean 
that the remote peer address for the LDP FEC will be included in the FEC 
Stack change sub-TLV for the RSVP FEC? I don't believe this implementation 
is suitable, or maybe this example is not suitable here. How to use this 
remote peer address field exactly?
IMHO, the Remote Peer Address is for the build of a LSP topology. However, 
if without this field in the FEC Stack change sub-TLV, there is no impact 
on the normal tracing procedures, and the LSP topology will also be build 
with the information from the other field in FEC Stack change sub-TLVs.

2. AFAIK, the FEC Stack change sub-TLV in the echo reply message is for 
the initiator to have a knowledge of the Target FEC change. As described 
in RFC4379 and draft-ietf-mpls-p2mp-lsp-ping-15, the initiator SHOULD copy 
the Downstream Detailed Mapping TLV into its next echo request. That means 
the FEC Stack change sub-TLV in the DDM TLV will be also in the next echo 
request message. I don't think the reciever need this sub-TLV in the echo 
request. So IMHO it is not necessary to contain this sub-TLV in the echo 
request message.

3. In the algorithm section 4.3.1.2, there missing a "{" at the end of 
line fourth
" while (sub-tlv = get_next_sub_tlv(downstream_detailed_map_tlv)) "

Thanks,
Zhi

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