Subject: RE: [SIP] A problem in SIP-NAT solution:

From: Satyanarayana T <[email-masked]>
Date: Thu, 22 Mar 2001 11:27:24 +0530

Absolutely. IP address, if it exists, in SIP headers too needs to be
replaced.
 
regards
Satya T

-----Original Message-----
From: YinShaoHua [mailto:[email-masked]]
Sent: Thursday, March 22, 2001 8:00 AM
To: [email-masked]
Subject: [SIP] A problem in SIP-NAT solution:

Hi,
In all the solution that handle SIP signalling through NAT or Firewall, the
IP address of SDP message is replaced but the address in SIP headers is not
considered. (Please see draft-ietf-sip-call-flows-03.txt or
draft-thernelius-sip-firewall-solution-00.txt) Actually, if the address of
the SIP headers is not replaced, it will lead to call failure also. 
                 _ _ _ _                                              _ _ _
_
                           \                                           /
A  (Private Address) |NAT1  (Public Address)   NAT2|  B  (Private Address)
                           /                                           \
                   -----
------
Regarding a special case of above figure. The A and B domain have private
address, perhaps, they have a same address plan. If one user(A1) of A domain
call a user(B1) of B domain through a Proxy(P1) of B domain(viz. A1 --> NAT1
--> NAT2 --> P1 --> B1 ), meanwhile, A1 and P1 have the same IP address in
different private address domain. Therefore, if we don't replace the address
of Via header of INVITE message when it go through NAT1, P1 will detect a
loop and then reject the call. 
From the above example, I think we should replace the IP address of SIP
headers also when SIP message goes through a NAT. Any suggestions are
welcomed! 
 
ShaoHua Yin
SIP Project,Signalling Department,
Huawei Co.LTD
Kefa Road
Science-Based Industrial Park
Nanshan District, Shenzhen,P.R.C
 
Shenzhen - 518057
 
Tel: 86-755-6544623
Fax:86-755-6544453
www.huawei.com <http://www.huawei.com>