Re: wrong transport selected

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 <
[email protected]> 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:[email protected] (172.22.0.20:6060) to sip:[email protected], 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)
>  Route-URI: sip:[email protected]: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)
> 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>
> 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
> 99(142) ERROR: <core> [core/tcp_main.c:4645]: handle_tcpconn_ev(): connect 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 failed
> what is wrong?
>
> Using tcp as a transport initially works well and NOTIFY is coming to the
> client.
>
> thanks in advance
>
>
> Andrei
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