Thanks, got it.. Just sounds like a bit strange behavior.. what the point switchover to TCP in case of SIP transport=udp. Obviously that there is no listener on client side accepting tcp and tcp connection was not established. Is such behavior covered by some RFC? what is expected from the client then ?

Anyway, will try

Andrei

On 6 Aug 2025, at 08:36, Supreeth Herle herlesupreeth@gmail.com wrote:

Hi Andrei,

If you are using default P-CSCF found in this location - https://github.com/kamailio/kamailio/tree/master/misc/examples/ims/pcscf then you may want to comment out the following parameters in kamailio.cfg file. This controls the switch to TCP protocol if the MTU of the received UDP packet exceeds 1300. But, keep in mind that replies to SIP INVITE from an IMS client can easily exceed MTU of 1500 and if even one fragment is lost or blocked (e.g., by firewall, NAT, or misbehaving middlebox), the entire SIP reply is lost.

udp_mtu = 1300 udp_mtu_try_proto = TCP

BR, Supreeth

On Mon, 4 Aug 2025 at 22:31, Andrei Fedorov via sr-users <sr-users@lists.kamailio.org mailto:sr-users@lists.kamailio.org> wrote:

Hello please advice what is wrong The scenario is following

Client get registred with p-cscf using udp as transport and ipsec enabled Registration completed successfully. Client send reg event SUBSCRIBE, and get 200 back But it do not get any notification then. In p-cscf container I am observing NOTIFY coming from s-cscf and then something strange happen

52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: PCSCF: NOTIFY sip:172.22.0.1:55822;transport=udp (sip:9076543210@ims.mnc001.mcc001.3gppnetwork.org mailto:sip%3A9076543210@ims.mnc001.mcc001.3gppnetwork.org (172.22.0.20:6060 http://172.22.0.20:6060/) to sip:9076543210@ims.mnc001.mcc001.3gppnetwork.org mailto:sip%3A9076543210@ims.mnc001.mcc001.3gppnetwork.org, 0ed4dd8c-89a5-42ac-80cb-690891a400f1) 52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: Within DLG 52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: Within loose route 52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: PCSCF MO_indialog: Destination URI: <null> Request URI: sip:172.22.0.1:55822;transport=udp 52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: Source IP and Port: (172.22.0.20:6060 http://172.22.0.20:6060/) Route-URI: sip:mo@172.22.0.21:6101;lr=on;ftag=b7f568fe 52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: Received IP and Port: (172.22.0.21:6101 http://172.22.0.21:6101/) 52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: Next hop domain: (172.22.0.1) 52(95) NOTICE: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} <script>: Contact header: <sip:scscf.ims.mnc001.mcc001.3gppnetwork.org:6060 http://scscf.ims.mnc001.mcc001.3gppnetwork.org:6060/> 52(95) INFO: {1 350779919 NOTIFY 0ed4dd8c-89a5-42ac-80cb-690891a400f1} ims_ipsec_pcscf [cmd.c:1187]: ipsec_forward(): new destination URI: sip:172.22.0.1:55822 http://172.22.0.1:55822/ 99(142) ERROR: <core> [core/tcp_main.c:4645]: handle_tcpconn_ev(): connect 172.22.0.1:55822 http://172.22.0.1:55822/ failed as you may see, request states transport=udp, Request URI: sip:172.22.0.1:55822;transport=udp while p-cscf then trying to use tcp?? 99(142) ERROR: [core/tcp_main.c:4645]: handle_tcpconn_ev(): connect 172.22.0.1:55822 http://172.22.0.1:55822/ failed what is wrong?

Using tcp as a transport initially works well and NOTIFY is coming to the client.

thanks in advance

Andrei __________________________________________________________ Kamailio - Users Mailing List - Non Commercial Discussions -- sr-users@lists.kamailio.org mailto:sr-users@lists.kamailio.org To unsubscribe send an email to sr-users-leave@lists.kamailio.org mailto:sr-users-leave@lists.kamailio.org Important: keep the mailing list in the recipients, do not reply only to the sender!