I have a VigorPhone 350 that connects across the internet to an IPPBX 2820 from a location with a Netgear router. Replace that router with a Draytek 2920 and the phone fails to register.

Running the latest released firmware on both the phone and the PBX and the router.

Any ideas why this is the case? When this first presented itself four or so months ago I phoned the IPPBX helpline and was told it would be fixed in the next firmware - but that is not the case.

So how do I get this to work?

Brian