After a router and internet connection change change a TGP 500 Voip System would not connect to the blueface.ie VOIP Service. On the same network a bunch of phones could connect to a VOIP system on Voicenet. On the TGP 500 the Orange Light flashed proving it was having issues connecting to the TFTP Server. I added port forward for every ports to the devices static IP to check if the inbound connection was the issue but still no success. I disabled SIP ALG on the router as this sometimes affects SIP however still no joy

I opened up the firewall to check the NAT sessions, and it only had one connected to the ISP’s DNS Server ( Zen ) so it was getting that far.

I changed the DNS server to Open DNS’s Servers: 208.67.220.222 and 208.67.222.220 , ( on the phone go to menu , IP Services , activated DHCP on the menu , then choose a Static DNS Server )

Rebooted the box and it worked straight away. Turns out the SRV record lookup on Zen’s DNS server was the issue …