[SIPForum-discussion] [Sip-implementors] Address change in "Via" field from private IP to public IP.

Srivastava, Gaurav Gaurav.Srivastava at inin.com
Fri Jun 14 06:58:28 UTC 2013

This is interesting Somesh,  maybe such a mechanism is involved after all. I wouldn't read much into the second REGISTER part as now I observe all the new REGISTERs going out with the public IP address.

Thank you so much for highlighting that, I will check if STUN (or a similar mechanism) is in place for the client to be aware of the public IP.

What if such a mechanism was not there , would I face problems ? The sip client (un aware of the public IP address) would send out REGISTER having my laptop's private IP in the contact & via headers - but I am sure some other device along the way would do the honours - I am just not sure which.

I am actually not facing any issues with this. I am having trouble with a PBX that I have which does not seem to be "aware" & sends out a REGISTER with its private IP in contact & via. Calls do not land on my PBX subsequently from the outside, public networks.

Thanks again!

Gaurav Srivastava | Senior Systems Engineer
phone | +61.449642846 | Gaurav.Srivastava at inin.com
Interactive Intelligence Inc.
Deliberately Innovative

-----Original Message-----
From: Shanbhag, Somesh (NSN - IN/Bangalore) [mailto:somesh.shanbhag at nsn.com] 
Sent: Friday, 14 June 2013 4:51 PM
To: Srivastava, Gaurav; SIP Implementors; discussion at sipforum.org
Subject: RE: [Sip-implementors] Address change in "Via" field from private IP to public IP.

Hello Gaurav,

May be your sip client is learning the IP address (NAT) via some mechanism like STUN etc. But I am not sure, why it only does for second REGISTER. May be its designed that way that after learning, during re-REGISTRATIONs it will use the learnt address.

One more interesting point - are you facing any issues with this? May be your organization NAT is SIP aware?


-----Original Message-----
From: ext Srivastava, Gaurav [mailto:Gaurav.Srivastava at inin.com] 
Sent: Wednesday, June 12, 2013 8:00 AM
To: SIP Implementors; discussion at sipforum.org
Subject: [Sip-implementors] Address change in "Via" field from private IP to public IP.


I am using a SIP soft phone (Zopier) that registers to Skype. The softphone sends out a REGISTER message to sip.skype.com for this.

While going through the messaging, I noticed that initially the via field contains my private IP address.

When the client re REGISTERs, the address changes from my private IP to the public IP which my organization has.

Please note that I am running the packet capture on my laptop.

I am trying to understand the change in IP address - please let me know if you have an understanding of this.

Warm Regards,
Gaurav Srivastava.
Sip-implementors mailing list
Sip-implementors at lists.cs.columbia.edu

More information about the discussion mailing list