UCM 6510 (in HQ) with GXP Phones in Remote-Sites


Hi there!
My Engish is not the best but i will give a try.

We have a UCM 6510 (IP: in the headquater LAN (IP:
We have remote offices connected with Sophos RED15 devices.
The remote office IPs are; …

All is working fine. But sometimes, some phones in the remote offices cant hear the caller.
All ports from ant to the remote offices are open.
In the UCM Package Log i see the communication is sometimes only in one direction.

My Question is:
Do the phones need any NAT settings on the Phones SIP Account Settings?
Do the Extension need NAT activated on the extension settings in the UCM?

Best regards!


Catch packets and see when they fail.
Both phones and UCM have this possibility.


What Sophos device are you using for firewall?


Hi. It is a Sophos SG with UTM 9.



We had an issue just over a year ago with the SGs and SIP, we couldn’t figure out the issue and neither could the Sophos techs. We ended up replacing them with another brand to get it to work. They may have fixed the issue by now, but I don’t use sophos very often in my SIP installs anymore. The older models worked great for us.

I’d do the captures on the UCM as @Marcin suggested and if you can’t see the issue I’d go to sophos.