SOLVED DNS resolver failure

[Mactabby]

I am getting an error in my overnight update: "All of the server’s DNS resolvers fail to respond". I currently have them set to Google's DNS, 8.8.8.8 and 8.8.4.4 and running the check_unreliable_resolvers --notify script gives me timeouts on every address. I have tried adding CloudFlare as a third, but it's obviously an issue with my server, not the resolvers. I've also noticed pings to external IP addresses report host unreachable.

However the server is online, all domains and websites functioning correctly and emails being sent, auto ssl being retrieved etc.

The only thing that has changed recently is the server IP address was migrated, and I've followed this through in WHM and all domain DNS records.

Where should I be looking to fix this?

Thanks

 

[cPRex]

Hey there! Can you ensure that port 53 is open for traffic on your machine with that new IP address? Without that port opened for traffic there will be odd behavior with the DNS system.

 

[Mactabby]

I believe it is - output from netstat:

tcp 0 0 0.0.0.0:53 0.0.0.0:* LISTEN 866/pdns_server

 

[cPRex]

netstat would only tell us what is happening locally. I like to use nmap to test specific ports from an external machine, with this command:

nmap -sU x.x.x.x -p 53

where "x.x.x.x" is the IP address of the server.

 

[Mactabby]

Hi - output from nmap as requested:


Host is up.
PORT STATE SERVICE
53/udp open|filtered domain


 

[cPRex]

That certainly looks normal to me. It might be time to reach out to your host to see if they have experienced any resolver issues if you are continuing to get that message nightly.

 

[Mactabby]

Just to close this, the problem was indeed with the hosts and they needed to tweak the routing and rebuild the network for me. All sorted now.

 

[cPRex]

Thanks for the follow up!

 

[hmaddy]

How to do this.??? can you please share its steps