Subject: [NSIS] WGLC comments for draft-ietf-nsis-ntlp-13.txt

From: "Christian Dickmann" <[email-masked]>
Date: Tue, 24 Apr 2007 23:03:01 +0200

Hi all,

During the last weeks I have been working on the interop test case
draft[1]. In the process I looked at almost all aspects of normal GIST
operation and also at some more rare ones. I have no major concerns and
as an implementor I can confirm that the spec can be implemented. GIST
seems to have some complexity, but being a general purpose signaling
transport protocol this is acceptable to me. As an implementor I can say
that the complexity is manageable. 

Here is a number of small issues (I mailed purely editorial issues
directly to Robert while they came up):
- I implemented the Legacy NAT detection given in Section 7.2.1 and it
works fine with a standard linux NAT. 

- However, the spec tells me (not just in the case of NAT Traversal) to
abort a 3-way handshake when I receive an Error message. The general
rules for error messages tell me to  send the message with NSLP ID = 0.
As GIST uses the triplet (MRI, SID, NSLP ID) to index the MRS-Table, I
do not know how to match the error message to the flow that is currently
performing the 3-way handshake. I could try all NSLP IDs, but I do not
see any reason why the error message shouldn't tell me which NSLP ID it
corresponds to. Or am I supposed to get that information from the
original Common Header echoed in the error message? A clarification in
Section 5.6 "Error Message Processing" would be nice.

- Section 7.2.1. "Legacy NAT Handling" does not discuss Q-Mode
encapsulated D-Mode messages. If there is no working solution here, that
should be made clear. If there is one, it should be in that section.

- I tried to implement the GIST-aware NAT traversal and ran into a
problem. See the separate mail on that issue.

- There seems to be some inconsistency regarding the setting of the
S-Flag for retransmissions.
On Page 55 the spec says (indicates MUST): " Note that all MRMs require
S=1 for at least some
   retransmissions, so ICMP errors related to fragmentation will be seen
   at the Querying node."
In Section 5.8.1.2 the spec says (says SHOULD): 
"     A node SHOULD use the flow source address for initial Query
      messages, but SHOULD transition to the signalling source address
      for some retransmissions or as a matter of static configuration,
      for example if a NAT is known to be in the path out of a certain
      interface."
In Section 7.2.1 (indicated RECOMMEND):
" note the Q-mode
   encapsulation rules recommend that S=1 is used at least for some
   retransmissions (see Section 5.8)."

I guess "SHOULD" is correct. 

Again, overall I agree with the current draft and would be happy to see
GIST proceed through the IESG review. The specification is very well
written, the technical problems have been well addressed, the complexity
is manageable and the specification can be implemented. In addition,
interoperable implementations exist and most features of GIST have been
tested in interop events.

Regards,
Christian Dickmann

[1]
http://user.informatik.uni-goettingen.de/~cdickman/draft-dickmann-nsis-n
tlp-interop-00.txt

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