Thank you for you answer.

We have tried to change the local port for Bob, but it doesnt change anything. And the contact value in 200 OK message has no influence in this case.

In fact, we have made a further investigation regarding the socket selection *and read the code. *The issue seems to be located in the RR module and the loose_route() function.

In the  after_loose() function in loose.c, the  function set_force_socket()  is called only if a DOUBLE route is mentioned in the route set of the ACK message

But when both users are using 5066 as proxy port, we get only ONE route for the proxy in the route set (and to us it is OK). In this case, we get a trace:

"No next URI found"

and the code exits. Later in the message processing, when t_relay() is called, the forward_request() selects the first socket defined in our configuration instead.

At this point, we can't presume what socket we be select. We believe that it is a software bug  and that after_loose() should force the send_socket even though we have only one route in the route set. We also checked the 5.1 code and there is no change in this module that would alter this behavior.

Are we missing something?

Thank you for you time,


Le 26/01/2018 à 15:43, Евгений Голей a écrit :

Could it be because of Bob happend to use 5060 as local port?
Yes, the port and the address in the ACK are indicated by what the value in Contact was in reply 200 Ok. Look at the message 200 Ok

    Четверг, 25 января 2018, 13:00 +03:00 от Thomas Carvello


    i have an issue with my Kamailio 4.1.9 configuration.

    This configuration is multi-homed, we have*two network*
    interfaces, one on a private network and on the public Internet.
    Kamailio is configured to listen on port 5060 and 5066 on both
    interfaces. We register two users Alice and Bob on the  public
    Internet using port 5066.  Both users are behind a NAT and we
    capture the SIP exchange on the proxy server.

    We have set the parameter mhomed=1

    When Alice calls Bob, we have

    Alice                       Proxy                           Bob

    src=5063            dst=5066
    INVITE ------------------>

                             ------  INVITE ---------------> dst=5060

                             <------- 200 OK -------------- src=5060

    <------- 200 OK --------- src=5066

    src=5063            dst=5066
    -------- ACK ----------->

                             *src=5060 (blocked by NAT)*
                             ------  ACK-----x            dst=5060

    The ACK packet gets relayed with the wrong source port. Then the
    NAT rejects the packet and the call cannot be established.

    For some reason, when Bob calls Alice, the call is correctly
    established. Could it be because Bob happend to use 5060 as local

    Also, if we set nhomed=0 it works BUT we are not sure that multi
    homed is handled correctly.

    I was wondering if you have encounter this issue before?

    I have investigated the code for selection socket and what is the
    logic of this selection ?

    /*How does kamailo knows that it should choose 5066 as src port if
    the user is registered using port 5066 instead of 5066?*

    Thank you for your time.


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