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Linux Server Deployment & SSH Mastery · Lesson

DNS Configuration and Troubleshooting

Understand how Linux servers resolve hostnames to IP addresses: configure resolvers, edit /etc/hosts, and use dig, nslookup, and host to diagnose DNS problems that break connectivity even when the network is fine.

Why DNS Matters on a Server

Your server can have perfect network and firewall settings yet still fail to reach the outside world if it cannot resolve names. DNS translates human-friendly hostnames like example.com into IP addresses.

Knowing how resolution works — and how to debug it — is essential network skill.

The Resolution Path

When a program needs an IP for a name, Linux checks sources in order, typically:

  • The local /etc/hosts file
  • Configured DNS servers (resolvers)

The order is governed by /etc/nsswitch.conf on the hosts: line.

grep hosts /etc/nsswitch.conf
# hosts: files dns

All lessons in this course

  1. Basic Network Configuration
  2. Understanding Firewalls (UFW/firewalld)
  3. Port Management & Security
  4. DNS Configuration and Troubleshooting
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