When encountering ping: www.example.com: Name or service not known errors, follow these diagnostic steps:

1. Verify Network Interface Status Check active interfaces and their configurations:

   ip addr show
   

   Example output showing a properly configured interface:

   2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500
       inet 192.168.1.100/24 brd 192.168.1.255
   

2. Test Basic Connectivity Confirm network layer functionality:

   ping 1.1.1.1
   

   Successful pings indicate DNS-specific issues rather than general network problems.

3. Inspect DNS Configuration Examine resolver settings:

   cat /etc/resolv.conf
   

   Valid configuration should include:

   nameserver 9.9.9.9
   nameserver 1.1.1.1
   

4. Validate Routing Table Check gateway configuration:

   ip route show
   

   Look for default route entries:

   default via 192.168.1.1 dev eth0
   

5. Restart Networking Services Aply configuration chenges:

   sudo systemctl restart networking
   

6. Verify Firewall Settings Check for DNS-related restrictions:

   sudo iptables -L -n -v
   

   For firewalld systems:

   sudo firewall-cmd --list-services