We have a relatively new phone system, using Polycom IP phones. Specifically, Polycom IP331 2-line phones. We also have a few cloud soft phones, as well as a Generic SIP Phone (AnyPhone).
We’ve had a few small power outages here, and that’s killed the power to the Comcast Cable modem, as well as the switch.
The error message was “URL dialing not available” or “DHCP failure” or “network is down” or “Unable to register.”
After this happens, the Polycom IP phones have trouble rebooting and re-connecting. These phones are supposed to be able to be plugged into any network (home, office, on the road) and just work.
The first time I called tech support, they told me to reboot everything, and that seemed to work.
But then it happened again, and five different reboots didn’t quite work. They still did not connect.
It seems that the phones were not able to use Comcast’s DNS service to translate the domain name to the proper IP address in order to work.
It looks like the main issue is that Comcast’s DNS servers – 184.108.40.206 and 220.127.116.11 – don’t always work well with iOT devices, such as Polycom IP phones.
This isn’t the first time I’ve had issues with Comcast’s DNS servers returning bad results. I’ve seen if Comcast’s DNS servers don’t connect and translate domains to IP addresses, it will shut off a whole section of Websites for Comcast users.
The fix: In the router, under the LAN/WAN section, I set the DNS servers instead to Google’s DNS servers: 18.104.22.168 and 22.214.171.124.
I didn’t even have to reboot everything, and all of the phones came back on.
I hope this helps…