Loop Detection Mechanisms for Session Initiation Protocol (SIP) Back-to-Back User Agents (B2BUAs)
draft-ietf-straw-b2bua-loop-detection-04

I'm really glad to see this moving forward (because I've also talked to some of the folk who have had the pleasure of Max-Forwards=70 meltdowns). The recommendations seem clear and reasonable, and I'm happy to ballot Yes, with one nosy question. (I also agree with Barry's comment, and think I agree with Pete's as well, but you've already seen those).

This text:

   If the received request did not contain a Max-Forwards header field,
   one MUST be created in any request generated in the UAC side, which
   SHOULD be 70, as described for Proxies in section 16.6 part 3 of
   [RFC3261].

points back to this text:

      3. Max-Forwards

         If the copy contains a Max-Forwards header field, the proxy
         MUST decrement its value by one (1).

         If the copy does not contain a Max-Forwards header field, the
         proxy MUST add one with a field value, which SHOULD be 70.

         Some existing UAs will not provide a Max-Forwards header field
         in a request.

in a proposed standard published in 2002. I'm looking at the definition in 20.22 Max-Forwards, which says 

   This header field should be inserted by elements that can not
   otherwise guarantee loop detection.  For example, a B2BUA should
   insert a Max-Forwards header field.

So, what I'm wondering is, and a "no" answer would terminate my questions, which are pipelined just to avoid roundtrip latencies :-)

- Are UAs that don't insert Max-Forwards still deployed? If so,

- Would a spiral back out to a proxy or B2BUA that doesn't insert Max-Forwards still be vulnerable to the endless looping problem that this draft is addressing? If so,

I wouldn't dream of asking you to figure out how to detect such a loop (and especially not when what you've already got is a huge improvement and doing so would hold you up), but I'm wondering if it would make sense to 

- point this problem out in the draft, and/or

- consider whether a short BCP on "omitting Max-Forwards considered harmful" would have any positive effect.