Network management requires machines to be able to communicate efficiently, and one of the simplest ways to achieve this is via domain names. But how does a machine know where to send traffic for any particular domain name? Without proper name resolution, communication becomes challenging—at best requiring humans to memorize IP addresses, and at worst causing a complete communication failure. By the end of this article, you will know how to configure name resolution on a Linux machine and ensure seamless communication across your network.

Let’s assume we have a network with the following machines:

  • Host A: 192.168.1.1
  • Host B: 192.168.1.11

These machines are all on the same network, with the switch address at 192.168.1.0.

Now, when we ping Host B from inside Host A, it responds. However, we’d like to be able to ping db directly using the following command:

ping db

Currently, running this command results in:

ping: unknown host db

Understanding Name Resolution

In this example, we want Host A to resolve db to Host B’s IP address. To accomplish this, we have two common options: the older method of adding an entry to the /etc/hosts file, and the more modern method of using a DNS server.

Local Name Resolution: /etc/hosts

For name resolution of db to Host B’s IP address, add the following entry in the hosts file on Host A at /etc/hosts:

echo 192.168.1.11 db >> /etc/hosts

Now, when db is pinged, the request goes to 192.168.1.11 (Host B’s IP address). In this case, Host A uses /etc/hosts as the source of truth and doesn’t care what Host B calls itself.

*Implications: This approach allows us to manually configure any domain name to any IP address. For example, we could map www.google.com to 192.168.1.11, and every time we try to go to www.google.com from Host A, it would actually go to Host B, not Google.*

DNS Servers: The Modern Approach

As networks grew, managing name resolution by editing the /etc/hosts file on each individual machine became too cumbersome. This is where DNS (Domain Name System) servers come into play. DNS servers act as a centralized source of truth for all machines on a particular network.

How to Point a Host at a DNS Server

Each machine has a DNS Resolution Configuration File located at /etc/resolv.conf. To point your machine to a DNS server, you can edit this file as follows:

echo nameserver 192.168.1.100 >> /etc/resolv.conf

This command tells the machine to use the DNS server at 192.168.1.100 to resolve hostnames to IP addresses.

What if There is a Conflict?

When both /etc/hosts and the DNS server contain the same name, the host will always look at /etc/hosts first. If the name is not found there, it then refers to the DNS server.

Important: This behavior can be modified by editing the /etc/nsswitch.conf file. The default configuration is:

hosts:   files dns

Here, files refers to /etc/hosts, and dns refers to the DNS server. If you reverse the order, the host will refer to the DNS server before consulting /etc/hosts.

What if the Name is in Neither?

If the name cannot be found in either /etc/hosts or the DNS server, the host will not be able to resolve it, resulting in an error like “unknown host.”

Using Public DNS Servers

A common choice is Google’s public DNS server, 8.8.8.8. You can add it to your /etc/resolv.conf file as follows:

echo nameserver 8.8.8.8 >> /etc/resolv.conf

Abbreviating Subdomains

Let’s say your company owns the domain mycompany.com, with subdomains like:

  • web
  • www

Typically, to access these subdomains, users would need to enter the full domain like http://web.mycompany.com. However, on your local network, you can configure your machines to resolve subdomains with just the short name (web), by adding a search entry in the /etc/resolv.conf file:

echo search mycompany.com >> /etc/resolv.conf

Now, simply entering web will resolve to web.mycompany.com.

You can even add multiple search domains:

search mycompany.com prod.mycompany.com

Linux will search through both domains in order before notifying you that the name cannot be resolved.

Conclusion

Whether you’re managing a small network or a large one, understanding how name resolution works and how to configure it properly can help you streamline communication between hosts. While the traditional /etc/hosts file method still works, modern networks rely heavily on DNS servers for scalable, centralized name resolution.

By leveraging both methods, you can optimize how machines in your network resolve names, improving efficiency and reducing potential conflicts.