Working on ims integration with the actual handset, have got a problem with ipsec establishment to complete registration. 

Initial steps are fine, including diameter exchange and 401 (with security server details) toward UE. On the next step UE and kamailio should establish ipsec connection, and UE to submit the next register with a response. As per trace UE is trying to establish the same (can see initial TCP SYN encapsulated onto ESP), using port-s, provided in Security-Server, but get an ICMP packet from server with destination/protocol unreachable. No more info either in P-SCSF log, no in kern.log. Proxy is listening to that port, it is tcp and available over telnet, so should not be a connectivity issue.

Please let know if any ideas how to troubleshoot that further,