Subject: [SIP] SIP & NAT Interoperability

From: "Dan Jones" <[email-masked]>
Date: Mon, 7 May 2001 13:50:05 -0400

Hi,

I've been looking in to some of the issues around supporting SIP behind a
NAT device, and would like to know if there are any formal discussions on
this list on the matter.  Can't find any in the archives.  If not - would
like to start the conversation:

There is the beginning of a trend I see in at least some vendors' SIP
clients to allow one to put the outside NAT ip address in the SIP headers
(contact, from, callID, eg), so the receiving station knows to whom to
reply.  While this works, it also breaks SIP connectivity if you're trying
to contact another SIP UA inside your firewall.  The simple fix seems to be
an algorithm on the SIP UA that says:

If pkt destined for inside NAT address
{	leave SIP headers alone

else

	replace contact address with outside NAT address is contact, from, callID,
etc fields
}

Has anyone looked at this, or know of any efforts to standardize a fix?

/dan

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---

From: "Medhavi Bhatia" <[email-masked]>
Date: Mon, 7 May 2001 13:54:56 -0400

Several pieces of work:

draft-davies-fw-nat-traversal-00.txt
draft-rosenberg-sip-entfw-01.txt

there are other references inside these drafts.