Re: Evaluation: draft-ietf-mmusic-sdp4nat - RTCP attribute in SDP to Proposed Standard

["Steven M. Bellovin" <smb@research.att.com>]

In message <200304021819.NAA21679@ietf.org>, IESG Secretary writes:
>
>Last Call to expire on: 2003-4-14
>
>	Please return the full line with your position.
>
>                    Yes    No-Objection  Discuss *  Abstain  
>
>
>Steve Bellovin      [   ]     [   ]       [ x ]      [   ]

The discussion in point (4) (of the three-step process....) in Section 
3.1 is, in fact, imposing a new requirement on NATs.  This document is 
a rather subtle place for such a requirment.  I believe that a separate 
"NAT Requirements to Support SIP" document needs to be written first.

Given that according to this document, only "a large fraction" of NATs 
behave in the desired fashion today, there needs to be discussion of 
how an application can discover that it is behind an older NAT.  The 
alternative is silent failures to connect, which aren't very 
user-friendly.  The abstract to this document should note that it 
depends on STUN servers being available.

		--Steve Bellovin, http://www.research.att.com/~smb (me)
		http://www.wilyhacker.com (2nd edition of "Firewalls" book)