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

[Johan Wilfer]

2013-06-27 16:53, Olle E. Johansson skrev:
>
> 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
>

Olle, you are the king. Thank you!

With mhomed=1 it works with the listen-directives.


Greetings from Västkusten :-)

-- 
Johan Wilfer