[SR-Users] Wrong src-adress in packets sent from Kamailio when using listen=

[Olle E. Johansson]

27 jun 2013 kl. 16:44 skrev Johan Wilfer <lists at jttech.se>:

> 2013-06-27 16:08, Andrew Mortensen skrev:
>> 
>> On Jun 27, 2013, at 9:50 AM, Johan Wilfer <lists at jttech.se> wrote:
>> 
>>> Hi!
>>> 
>>> I've the following setup: Teleco <-> Kamailio <-> Asterisk(s)
>>> 
>>> The proxy has one public IP (say 1.2.3.4) and one private (10.0.0.1).
>>> The asterisk-pbx:es has private adresses (10.0.0.2 in this example)
>>> 
>>> I noticed that if I bind like this in kamilio.cfg
>>> listen=tcp:1.2.3.4:5060
>>> listen=udp:1.2.3.4:5060
>>> listen=tcp:10.0.0.1:5060
>>> listen=udp:10.0.0.1:5060
>>> 
>>> Then if a call comes in from the Telco to Kamailio (1.2.3.4), kamailio should forward the SIP-packet from it's private address (10.0.0.1) to asterisk (10.0.0.2)
>>> 
>>> However, the source address of the packets sent from Kamilio to Asterisk is wrong - it uses the public ip. Like this (tcpdump output):
>>> 
>>> 15:02:08.999642 IP 1.2.3.4.sip > 10.0.0.1.5060: SIP, length: 1346
>>> 15:02:09.474525 IP 1.2.3.4.sip > 10.0.0.1.5060: SIP, length: 1346
>>> 15:02:10.474524 IP 1.2.3.4.sip > 10.0.0.1.5060: SIP, length: 1346
>>> 15:02:12.474525 IP 1.2.3.4.sip > 10.0.0.1.5060: SIP, length: 1346
>>> 
>>> Obviously kamailio doesn't get any answers here. The packet goes out of the right interface, but with the wrong src-address.
>>> 
>>> However, if I remove the lines with "listen=" in kamailio.cfg to allow kamilio to bind to all interfaces the src-address is correct and everything works!
>>> 
>>> (I've also done some tests with icmp and telnet and the src-addr seems right in all these cases.)
>>> 
>>> Is this a bug or am I missing something here?
>> 
>> It sounds like what you want is force_send_socket:
>> 
>> 	<http://www.kamailio.org/wiki/cookbooks/4.0.x/core#force_send_socket>
>> 
>> andrew
> 
> Hi Andrew,
> Thanks for the tip!
> 
> My kamailio get the routing from a database, and then rewrites the R-URI with $ru = "sip: ...";. And then Kamailio resolve this domain and does all the magic. :-)
> 
> If I need to script a code-path for all these different cases I think the best way for me is to remove the listen=...-directives. Because I just want the src-address to be the "right" address (the same as the interface). Right now kamailio uses the right interface for the destination, but uses the source-ip of another interface.
> 
> 
> Is there a reason Kamailio just pick one address (of random? the first?) of all addresses when using "listen=", but can determine the right src-address when no "listen="-lines are present?
> 
> If this is a limitation with the listen-directive, I guess it's better to bind to all (no listen=) and use iptables to block access to some of the addresses, correct?

Have you enabled multihoming?
http://www.kamailio.org/wiki/cookbooks/4.0.x/core#mhomed

/O