Yes, you are right.I just couldn't understand the relation between children and IPsec port/spi ranges. Regards,Hossein On Tuesday, June 1, 2021, 02:48:07 AM PDT, Henning Westerholt <hw(a)skalatan.de> wrote: Hello,   not sure why you think that the ims_ipsec_pcscf module is listening only on UDP. It seems to be also listening on TCP:                           //add listen interfaces for IPv4                         if(add_listen_iface(addr4, NULL, ipsec_client_port + i, PROTO_TCP, 0) != 0) {                                 LM_ERR("Error adding listen ipsec client TCP interface for IPv4\n");                                 return -1;                         }                           if(add_listen_iface(addr4, NULL, ipsec_server_port + i, PROTO_TCP, 0) != 0) {                                 LM_ERR("Error adding listen ipsec server TCP interface for IPv4\n");                                 return -1;                         }                           if(add_listen_iface(addr4, NULL, ipsec_client_port + i, PROTO_UDP, 0) != 0) {                                 LM_ERR("Error adding listen ipsec client UDP interface for IPv4\n");                                 return -1;                         }                           if(add_listen_iface(addr4, NULL, ipsec_server_port + i, PROTO_UDP, 0) != 0) {                                 LM_ERR("Error adding listen ipsec server UDP interface for IPv4\n");                                 return -1;                         }   Cheers,   Henning   -- Henning Westerholt –https://skalatan.de/blog/ Kamailio services –https://gilawa.com   From: sr-users <sr-users-bounces(a)lists.kamailio.org>On Behalf Of H Yavari Sent: Thursday, May 20, 2021 3:01 AM To: Kamailio (SER) - Users Mailing List <sr-users(a)lists.kamailio.org> Subject: [SR-Users] IMS IPSec does use UDP socket?   Hi to all,   I am interested in the implementation of IPsec module. When I run Kamailio, it is creating processes based on the below formulate:   UDP children * IPSEC_MAX_CONN * interfaces (v4 and v6) + (TCP+UD) processes for each interface.   For example:    children = 16 tcp_children=16 IPSEC_MAX_CONN = 25 and two interface : IPv6 and V4   Kamailio process count = (16 * 25 * 2 ) + 16 + 16 = 832   But why IPsec module is listening to UDP not TCP? this is an internal connection?       Thank you.   Regards, Hossein