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

[Johan Wilfer]

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?


-- 
Johan Wilfer