[SIPForum-techwg] SIPConnect and IP addresses in Via headers

[Chris Sibley]

Hi Michael,

Sorry the delay in responding. Things have been pretty quiet on the list
as-of-late, thus I haven't been checking for new messages very
frequently.

That said, good observation! This didn't come up during the draft
review, but I agree with you that the publicly routable address
requirement should really only apply to the top-most Via: header. 

Assuming that no-one objects, I will make a note of this and add some
clarifying text to a future release of the specification.

Thanks!

--Chris

> -----Original Message-----
> From: techwg-bounces at sipforum.org [mailto:techwg-bounces at sipforum.org]
On
> Behalf Of Michael Procter
> Sent: Friday, November 03, 2006 6:44 AM
> To: techwg at sipforum.org
> Subject: [SIPForum-techwg] SIPConnect and IP addresses in Via headers
> 
> I have been reading sf-draft-twg-IP_PBX_SP_Interop-sibley-sipconnect
> version 5, and have a question about a statement in section 9 -
Firewall
> and NAT traversal.
> 
> The draft states that:
> 	Any IP address contained within the headers ... of SIP messages
> exchanged between the Service Provider and the Enterprise networks
> MUST be a publicly routable address.
> 
> My question is whether this is too strict.  The scenario I have in
mind
> is one where there is a UA connected to an IP-PBX that is implemented
as
> a proxy.  A message sent from the Enterprise network to the SP will
> therefore have multiple Via headers (2 or more).  I can clearly see
why
> the topmost Via of the message at the point of egress must be publicly
> routable, but why do any others need to be?
> 
> I can see why it might be desirable to only expose public IP addresses
> (e.g. for topology hiding), but that doesn't seem to be what this
> section is saying.
> 
> Can anyone shed light on what I am missing please?
> 
> Regards,
> 
> Michael
> 
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