Re: [straw] WGLC Comments on draft-ietf-straw-b2bua-loop-detection-02

[Hadriel Kaplan <[e-mail]>]

Hi Andy,
Thanks for reviewing!  Comments below...

On Sep 19, 2013, at 5:24 AM, "Hutton, Andrew" <[e-mail]> wrote:

> I have a couple of comments.
> 
> 1. Section 4 states " It is RECOMMENDED that B2BUAs implement the loop-detection mechanism for the Via header field, as defined for a Proxy in [RFC5393]."
> 
> This could be changed to a MUST requirement by changing it to "B2BUAs MUST implement the updates to [RFC3261] for strengthening the requirements to perform loop detection as specified in [RFC5393]".  I prefer this because it enforces the requirement that some form of loop-detection must be in place when forking.

This was raised back in June here:
http://www.ietf.org/mail-archive/web/straw/current/msg00127.html

I'm fine with changing it to a MUST, but would like to hear more folks weigh in.  

As an aside, I'm fairly sure changing it to a MUST won't make B2BUA's implement that check, because some B2BUAs literally can't do it safely; that check requires knowing what all of the variables used for routing requests are, and it's not technically possible to know that in some architectures.  For example, if your architecture allows using external systems/routing-engines, or scripts/plugins, or something flexible like that to control SIP request routing decisions... then I don't think you can safely preform that via header check. (by "safely" I mean accurately enough to detect legitimate spirals vs. loops)


> 2. Section 5 states " B2BUAs MAY perform the same actions for in-dialog requests, but doing so may cause issues with devices that set Max-Forwards values based upon the number of received Via or Record-Route headers"
> 
> I think this could do with some more explanation regarding mid-dialog requests and the issues associated with setting Max-Forwards based on Via or Record-Route. It would be good to remove this "MAY" and have clear requirements for handling mid-dialog requests. Do we really need to have the text about setting based on the number of via or record-route headers?

I'm not sure I understand what you mean.  This doc is about B2BUA handling copying the Max-Forwards, not about the originating UAC setting the MAx-Forwards.  The text in this section was based on this:
http://www.ietf.org/mail-archive/web/straw/current/msg00157.html

-hadriel