If you are experiencing slow DNS performance on a Linux system with both IPv4 and IPv6 configured firewall, there are several steps you can try to troubleshoot and improve DNS performance:
Check the DNS server settings and make sure that the correct DNS servers are being used. You can check the DNS server settings in the /etc/resolv.conf file.
Check the firewall rules and make sure that DNS traffic is allowed through the firewall. You can check the firewall rules using the iptables or firewalld command, depending on the firewall software being used.
Check the network connection and make sure that there are no issues with the network hardware or configuration.
Check the DNS cache and make sure that it is being used effectively. You can use the dig or nslookup command to test DNS cache performance.
Check the DNS logs and make sure that there are no errors or issues with DNS queries or responses.
If you are using a caching DNS server, such as BIND or dnsmasq, make sure that it is configured correctly and that it is performing well.
By following these steps and reviewing the documentation, you should be able to troubleshoot and improve DNS performance on your Linux system with IPv4 and IPv6 configured firewall.