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

[Abinash Sarangi]

Hi Gaurav,
please see what is the AOR status of this endpoint in your server(cli command would help). on or before expiration if the client is re-registering , check the AOR now..are you getting a "received=<IP>" and rport=<port> in the Via header in the response packet. that would clearly mention if the NAT is sip aware ..

Thanks

-Abinash 


Date: Sat, 20 Jul 2013 23:10:11 +0530
From: rudra.k1 at gmail.com
To: Gaurav.Srivastava at inin.com
CC: discussion at sipforum.org; somesh.shanbhag at nsn.com; sip-implementors at lists.cs.columbia.edu
Subject: Re: [SIPForum-discussion] [Sip-implementors] Address change in "Via" field from private IP to public IP.

Hi Gaurav,

I think what you are seeing with your registration attempts to Skype is a standard. With what I have read in you explanation, I am expecting that when you see your public REGISTER message, you would find another via header appended over there while yours private IP would have got stacked down.


This new VIA IP would be your proxy or B2BUA, which could also have NAT functionality. The idea is that your REGISTRAR is sitting over Internet and there is no way for it to recognise your private IP. So, your B2BUA/ Nat server provides its IP in the 1st VIA header so that all responses from the Skype 1st hits this server and thereafter, your server can uniquely route the response to your private IP.


I am also expecting the presence of Record-Route headers in the going out requests and for all subsequent request a ROUTE header imbibed-into as well. The afore-stated details should be aptly seen if you have a trace running on your B2bUA/NAt server else you may not see all dialogs together and the sniffer which you are taking would only explain how the end-client sees tings.


Now, coming to your attempts to register to a PBX which doesn't let you get the calls. I would like to get a little more details about it to understand what is happening.

I hope the above explanation would have added value.


Regards,
Rudra


On Fri, Jun 14, 2013 at 12:28 PM, Srivastava, Gaurav <Gaurav.Srivastava at inin.com> wrote:

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

www.inin.com/au-nz



-----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?



Br,

Somesh



-----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.



Hi,



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.

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