How do I troubleshoot DNS resolution failures?

If the server can connect to IP addresses but cannot resolve domain names, the cause is usually DNS configuration or firewall rules.

Confirm whether it is a DNS issue

Run:

nslookup example.com
dig example.com
dig @1.1.1.1 example.com

If resolution works when a public DNS server is specified, the default DNS configuration may be abnormal.

Run:

cat /etc/resolv.conf

If you have used proxies, WARP, or one-click scripts, DNS settings may have been changed.

If the system firewall blocks DNS requests, resolution can also fail. Check whether UDP/TCP port 53 is restricted.

When submitting a ticket, please provide resolv.conf, nslookup or dig output, and screenshots of firewall rules.