I have a UC520 system setup with a SIP trunk to an ITSP. When my number goes out and registers with their system, it is using a random source port. the next time it registers it will create a duplicate registration and use a different port, then incoming calls start failing because the source port in our ITSP's database is wrong.
How can i get my lines to force registration from port 5060? why would they be coming from random ports? I have a CBAC firewall running inspecting SIP traffic, as well as UDP router-traffic. I tried disabling the sip inspection incase it was causing the port issue, with no change.
For now I have disabled registration (which is not required by our provider), but I would like a better solution.