Tech Tutorial: Manage Basic Networking - Configure Hostname Resolution #

Introduction #

The ability to configure hostname resolution is a fundamental skill for any systems administrator, especially for those preparing for the Red Hat Certified System Administrator (RHCSA) exam. Proper configuration of hostname resolution ensures that your systems can locate and communicate with other computers and services on a network. This tutorial focuses exclusively on Red Hat Enterprise Linux (RHEL), providing the necessary steps and commands to configure hostname resolution effectively.

Step-by-Step Guide #

1. Understanding Hostname Resolution #

Hostname resolution is the process of mapping hostnames to IP addresses. This is typically handled in two ways on a Linux system:

• Static resolution: Using the /etc/hosts file.
• Dynamic resolution: Using DNS (Domain Name System).

2. Configuring the /etc/hosts File #

The /etc/hosts file is one of the first resources consulted during hostname resolution. It contains static mappings of IP addresses to hostnames. This method is quick and does not rely on network availability, making it ideal for small networks or for providing overrides of DNS data.

Viewing the Current Hosts File #

To view the current entries in your /etc/hosts file, use the cat command:

cat /etc/hosts

Editing the Hosts File #

To add or modify entries, you’ll need to edit this file using a text editor like vi:

sudo vi /etc/hosts

Add entries in the following format:

<IP-address> <hostname> <alias(optional)>

For example:

192.168.1.10    server1.example.com    server1

Save and exit the editor (:wq in vi).

3. Using DNS for Hostname Resolution #

DNS provides dynamic hostname resolution and is configured by specifying DNS servers and search domains in the network configuration.

Configuring DNS Servers #

To configure DNS servers on RHEL, you will typically edit the network configuration file for your connection. For systems using NetworkManager, this is often managed via the nmcli tool.

Listing Available Connections #

nmcli con show

Modifying a Connection to Use Specific DNS Servers #

sudo nmcli con mod "System eth0" ipv4.dns "8.8.8.8 8.8.4.4"
sudo nmcli con up "System eth0"  # Restart the connection to apply changes

Replace "System eth0" with your connection name and "8.8.8.8 8.8.4.4" with your preferred DNS servers.

Setting the Search Domain #

The search domain is used to qualify short hostnames into fully qualified domain names (FQDNs).

sudo nmcli con mod "System eth0" ipv4.dns-search "example.com"
sudo nmcli con up "System eth0"  # Restart the connection to apply changes

4. Verifying Configuration #

After configuring hostname resolution, it’s important to verify that your settings are working correctly.

Testing with ping #

Use ping to check if the hostname resolves and responds:

ping server1.example.com

Checking Resolution Mechanism #

The getent command can be used to see how a hostname is resolved, whether via /etc/hosts or DNS:

getent hosts server1.example.com

Conclusion #

Properly configuring hostname resolution is essential for ensuring reliable network communication within your RHEL systems. By understanding and managing both static entries in the /etc/hosts file and dynamic DNS settings, you can maintain robust and flexible network configurations. Always remember to verify your settings to avoid any connectivity issues. This knowledge not only prepares you for the RHCSA exam but also equips you with practical skills essential for any Linux systems administrator.