Sip Trunk Registrations...

[womble1]

I have an odd problem...
Just installed a new Zyxel P-661H router and it will not allow sip trunk registrations...
IAX trunks fine...
Sip-trunk in fine, phones inside can register by sip with servers outside and phones outside can register with our server inside...
Only sip trunks seem to fail...
it looks like a DNS issue...
[2009-09-27 18:25:25] NOTICE[6474] chan_sip.c: -- Registration for '*******@sipgate.co.uk' timed out, trying again (Attempt #33)
I have sip trunks with other providers and they are fine, change router and all is fine...
used netconfig to set DNS to outside DNS provider..
obviously something odd is going on but what could it be ??

 

[womble1]

Ok no thoughts ?
everything else works all other services on all other servers but not this one thing...
in Asterisk info > sip info
under Sip Registery I can see this for all sip trunks...

sipgate.co.uk:5060 ******** 120 Request Sent

And that is it...
under sip peer the same trunk looks like this...

old/******** 217.10.79.23 N 5060 OK (56 ms)

and in the main admin / status window...

IP Trunk Registrations 0

I don't even know what to look for...

What is stopping at the router here...?

Can someone give me a clue as to what I am looking for ?
Thanks...