SIP sending internal IP instead of Public

I do not think that NAT is able to alter the SIP-Header and unfortunately the UTM has only an SIP helper implemented. For this kind of SIP manipulation you usually need a proper SIP Proxy or Session Border Controller.

Hi Joerg-ST,

Holger Gran is correct.

what you require is SIP ALG, usually a modern phone system is NAT Aware and can adjust the packet without getting a firewall involved.

As this can be temperamental. I have never used this as it usually causes issues.

The only article I can find is;

https://support.sophos.com/support/s/article/KB-000034975?language=en_US

It may well work, but have never tried it.

Hi Joerg-ST,

Holger Gran is correct.

what you require is SIP ALG, usually a modern phone system is NAT Aware and can adjust the packet without getting a firewall involved.

As this can be temperamental. I have never used this as it usually causes issues.

The only article I can find is;

https://support.sophos.com/support/s/article/KB-000034975?language=en_US

It may well work, but have never tried it.

I've had that work before, Argo, but I've seen more situations where the UTM SIP helper wasn't compatible with a VoIP provider and had to create new Services, Host/Network definitions and firewall rules manually.

In this case, Malcolm, it sounds like your internal VoIP device configuration is the problem - it should have your public IP in the SIP header., not its local IP.  This type of issue is not uncommon with IPsec VPNs.

Cheers - Bob