Re: [straw] AD review of draft-ietf-straw-sip-traceroute-02

[Hadriel Kaplan <[e-mail]>]

On Apr 11, 2014, at 3:29 PM, Richard Barnes <[e-mail]> wrote:

> If B2BUAs implement this spec as-is, then they'll see Max-Forwards: 0 and answer the call -- they don't know whether this is part of a traceroute or not.  So if a legacy UAC sends out a normal, non-traceroute, INVITE with loopback, and it happens to time out at one of these B2BUAs, and the UAC doesn't know to check for the Reason header for this value (because it's legacy), then it ends up talking to the B2BUA instead of the UAS.

Good point. So that's another benefit then. B2BUAs solve call failure problems they didn't even know existed.
;)

Actually, getting back to serious mode, that could happen even without this draft. Max-Forward handling in B2BUAs has always been undefined behavior until the loopback draft, afaik.


> It seems like in order to resolve this, you need to either:
> 1. Require UACs that use loopback to check for Reason (and thus update RFC 6849)

I'm fine with that.  Another option is to re-title this draft to be "Media-Loopback Usage in SIP" and add some text about that in general too.


> 2. Add some consent flag to the INVITE so that the B2BUA can tell traceroutes from other INVITEs

It won't help solve the problem you raised fully - it will help if all B2BUAs along the path implement this draft, but not if they just implement RFC 6849. Because they can still answer calls based on policy, and Max-Forwards=0 technically doesn't apply to them as a UAS unless they also implement the loopback draft.

-hadriel