External IP address issues?

I have had Asterisk 1.2.17 running OK for a while on a WRT54GL router behind a DSL604+ router/modem. The DSL 604+ was acting as proxy DNS server for Asterisk. However something wasn't quite right with my externip address as the IP address wasn't updating or the DSL604's DNS server was locking up. (Apparently common on these things.) I decided to disable the proxy server and hey presto 5 minutes later everything is broken. I then tried externhost/externrefresh and every other setup including reverting to how it was. Either way my SIP debug log now reports the Via address as an internal ip address, is that right?
Via: SIP/2.0/UDP 192.168.0.3:5060;branch=z9hG4bK32c926f0;rport
From: "asterisk" <sip:asterisk@88.251.xxx.xxx>;tag=as4a715be7

When I check my registration in Sipgate the IP address shown is also my internal address. I am really not sure what has happened but I cannot receive incoming calls anymore? Anybody now how to fault find what I have screwed up?

So the answer was to put the DSL604 router into bridge mode so it becomes a modem. Problem solved.