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Linux Networking Interview Questions

Networking knowledge is essential for configuring servers and troubleshooting connectivity issues.

Core Questions​

1. How do you check open ports on a Linux server?​

You can use netstat or the newer ss command.

ss -tuln
# or
netstat -tuln

Flags: -t (TCP), -u (UDP), -l (listening), -n (numeric ports/IPs).

2. What is the purpose of /etc/hosts and /etc/resolv.conf?​

  • /etc/hosts: Used for local DNS resolution. It maps IP addresses to hostnames locally, bypassing external DNS servers.
  • /etc/resolv.conf: Configures the system's DNS resolver, specifying which nameservers to query for domain resolution.

3. How do you troubleshoot network connectivity?​

  1. Check interface status: ip a
  2. Test local gateway: ping <gateway_ip>
  3. Test internet routing: ping 8.8.8.8 or traceroute 8.8.8.8
  4. Test DNS resolution: dig google.com or nslookup google.com

Practical Examples​

Changing an IP address temporarily:

sudo ip addr add 192.168.1.50/24 dev eth0

Best Practices​

  • Modern Tools: Mention modern iproute2 commands (ip a, ss) over deprecated net-tools (ifconfig, netstat) to show up-to-date knowledge.
  • Methodology: When asked how to troubleshoot, outline a systematic step-by-step approach from OSI layer 1 up to layer 7.