Private IPv4 addresses and internal DNS hostnames. A private IPv4 address is an IP address that's not reachable over the Internet. You can use private IPv4 addresses …

Certain website suddenly not reachable with cloudflare dns Sep 20, 2019 Find out why you can't access a website or service on the Feb 08, 2018 server not reachable - Hewlett Packard Enterprise Community

It seems that web service isn't up and running or it is not listening on right port or it is listening just on address. Check it with 'sudo netstat -tnlp' command. You should see process name, what IP and port it is listening on.

Nov 24, 2017 Pihole server not reachable (port 53) : pihole Pihole server not reachable (port 53) Hi Guys, i'm facing an issue with pihole server running on my rpi server (ubuntu mate). I was just checking the Pihole web gui and noticed that none of my LAN clients are listed there, the only client which is using the pihole as DNS server is the localhost (server itself).

How To Fix The “DNS Server Unavailable” Error

This was not caused by any changes to the site code, it was a DNS issue. If your site and DNS servers are on the same machine, and you have admin access to it, you can check its uptime to see if it was rebooted. Also, if your site and DNS are on the same server, you should consider using multiple nameservers to reduce possibilities of DNS failure.