Trunk between 2 freepbx works only using TCP

Hi guys, i have this strange problem.

I have 2 SIP trunks to connect 2 pbx.
Using TCP protocol the packets arrive to destination and the trunks are on-line.
Instend using udp there is no trace of packets incoming to the destination PBX and the result is “status UNREACHABLE”.
Possible that the same NAT settings works for tcp and not for udp?
The trunks works over ipsec and all traffic in the tunnel is permitted.

In the PEER details i use this simple configuration
host=192.168.101.3
username=usernamexxxx
secret=passxxxxx
type=friend
qualify=yes
context=from-trunk
transport=udp

Any advice is welcome!!!