Problem with ipsec setting of Via for outgoing message - sr-users

24 Mar 2025


      Hello,
I'm using Kamailio ver. 5.8.4.
I configured the ims_ipsec_pcscf with
modparam("ims_ipsec_pcscf", "ipsec_max_connections", 1)
and call ipsec_forward with flag = IPSEC_FORWARD_FLAGS
where :
# - IPSEC_SEND_FORCE_SOCKET 1
# - IPSEC_FORWARD_USEVIA 256
#!define IPSEC_FORWARD_FLAGS 257
For the UE REGISTRATION I have the following flow
UE                                        PCSCF_GM_IMS
                  REGISTER                                          
(32133)         ------------------>     (5060)                
                  100 Trying                                        
(32133)         <------------------       (5060)                
                  401 Unauthorized                              
(32133)       <------------------      (5060)               
                  REGISTER        (TCP)                          
(PORT_UC)  ------------------>     (PORT_PS)          
                  100 Trying       (TCP)                           
(PORT_UC)   <------------------     (PORT_PS)            
                  200 OK            (TCP)                           
(PORT_UC)   <------------------     (PORT_PS)            
------------------------------------------------------------------
                  SUBSCRIBE      (UDP)                         
(PORT_UC)   ------------------>      (PORT_PS)           
                  200 Subscription (UDP)                       
(PORT_US)   <------------------     (PORT_PC)              
                  NOTIFY            (UDP)                          
(PORT_US)   <------------------     (PORT_PC)               
                  200 OK            (UDP)                         
(PORT_UC)   ------------------>     (PORT_PC)              
                  NOTIFY            (UDP)                          
(PORT_US)   <------------------     (PORT_PC)
                  200 OK            (UDP)
(PORT_UC)   ------------------>     (PORT_PC)
                  NOTIFY            (UDP)
(PORT_US)   <------------------     (PORT_PC)
                  200 OK            (UDP)
(PORT_UC)   ------------------>     (PORT_PC)
The SUBSCRIBE behavior is correct : PCSCF receives message on PORT_PS and sends on PORT_PC
The NOTIFY behavior is wrong: PCSCF send from PORT_PC (correct), but UE respond towards PORT_PC, defined in the Via of the NOTIFY.
I know I can use the set_advertised_port() function, and in this case can work, but the function is taking a constant as a parameter, not a variable. This is causing a problem
when ipsec_max_connections > 1. In that case it won't be easy to pass the correct port.
I was wondering if the ipsec module should properly set the VIA port to the correct PORT_PS, rather than leaving the setting of the correct port by the kamailio.cfg.
Do you have any hints on that?
Thanks