Needing some assistance, please. Long story short I setup a small domain/network for a friend of mine just over 2 years ago for a dentist office. Everything has been working great until a couple weeks ago when he send me a screenshot of a DNS issue on one of his client machines. Upon further investigation I discovered that the domain/dns server was unable to access the internet all of the sudden. The only way we can get internet access back is to hardcode the ISP's DNS servers. If I leave the server pointed to itself (the actual IP, not the loopback) I cannot access the internet.
DNS is a bit of a grey area for me and I'm kind of at a loss, and not sure what has changed that would have impacted something that had been working fine for the past couple years.
I'm using a Westell 7500 modem provided by our ISP/CenturyLink that is setup in bridge mode to the PPPoE connection to our SonicWall TZ100 firewall. Any ideas what I need to do to get my server seeing the internet again without having to hardcode the ISP's DNS? This is affected clients that are setup to grab the IP via DHCP as it's set to point the server IP, so on each client I've had to also hardcode the DNS information to the ISP's DNS servers.
Any ideas would be greatly appreciated. Again I'm not real familiar with DNS servers so I'm not sure if I can just recreate a zone or how I can verify/narrow down where the issue is.
Hoping someone might be able to steer me to the path of having a working DNS server again.
Thanks for your time!