Re: [SR-Users] how to extract the ip address in the via header received paramter - sr-users

13 Mar 2013

Hi Daniel,

Thanks for your response. But I don't want the IP in the received parameter of the
incoming request. 
Instead, I want to read it (i.e. the public IP address of my own network where the local
user and Kamailio are located) from the incoming response received from another proxy
located outside the network. And I need that because Kamailio strips the top most via
(where the received parameter is present ) in the incoming response before sending it back
to the local user, which I guess is correct. But the user needs to know that IP address.
So we are planning to send that IP address in a custom header in the response back to the
user.

After going through some Kamailio documents I found that $sel(via.received) would return
the IP address in top most via of a message. Can I store it in a variable inside
onreply_route[MANAGE_REPLY] block and use that variable later in some appropriate route
block to insert a new header in the response to the local user? 

Can I do something as given below to fetch and store the IP address from received
parameter in the via header of incoming response

onreply_route[MANAGE_REPLY] {
...
if(search_hf("Via", "received", "f")) {
		xdbg("received param exists on top most via header \n");
		$var(public_ip) = $sel(via.received);
	}
...
}

and insert a new header as given below in an appropriate route block which is executed
while sending response back?
append_hf("My-custom-hdr: $var(public_ip) \r\n");

I am not sure if this logic would work. Is the $var() variable retained through two
different sip transactions? And which route block should be used to insert the header as
mentioned above? Please help.

Thanks,
Ajay

Hello,

the received parameter is constructed from source IP of the incoming request. You get it
via $si script variable.

Cheers,
Daniel

On 3/12/13 7:22 PM, Ajay Sabat wrote:
...

 Hi,

 I want to extract the IP address in the received parameter of the top 
 most via header of a response and use that in a custom header while 
 sending response back to the caller. Can somebody please tell how to 
 implement that in the Kamailio configuration file?

 I need to handle a NAT traversal scenario without enabling NAT in 
 Kamailio which is used as the proxy server. The caller which is in the 
 same network as Kamailio first sends a OPTIONS request to the callee 
 before sending the INVITE. It uses the public IP address returned in 
 the custom header of the OPTIONS response to build the contact header 
 and SDP of the INVITE request. In fact, it first looks for the IP 
 address in the received parameter of the via header to do that. But 
 Kamailio removes the top most via with received parameter and then 
 sends the OPTIONS response back to the caller. So we are using a 
 custom header for that purpose.

 I would appreciate other suggestions to achieve this in Kamailio, may 
 be by enabling NAT or some other alternative.

 Thanks,

 Ajay

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