Static IP Configuration on Linux

1. Gathering Your Network Information

Before making any changes, a good administrator always assesses the current situation. You need to know your network's layout to assign a valid static IP. Let's find out three key pieces of information: your current IP address and interface name, your network's default gateway, and a working DNS server.

The following video demonstrates how to find this information on an Ubuntu server.

Let's recap what you just saw and apply it to your virtual machine:

1. Find your interface name and current IP:
   Run ip a or ip addr.
   You will see a few interfaces. The loopback interface is named lo. The main network interface will have a name like eth0, ens33, or something similar. It will also have an inet address, which is your current IPv4 address assigned by DHCP.

   • Note down your interface name (e.g., ens33).
   • Note down your current IP address and its subnet mask (e.g., 192.168.38.129/24). The /24 is CIDR notation for the subnet mask 255.255.255.0. Your ECE background should make this familiar.

2. Find your Default Gateway:
   Run ip route.
   Look for the line that starts with default via. The IP address on this line is your gateway. This is the router your server uses to communicate with the internet.

   • Note down your gateway address (e.g., 192.168.38.2).

3. Choose a Static IP Address:
   You need to pick an IP address that is on the same subnet as your current IP but is not already in use. For a lab environment, a simple way is to pick an address with a high last number (e.g., 192.168.38.200) that is unlikely to be assigned by DHCP.

Now that you have your interface name, a chosen static IP, the subnet mask, and the gateway address, you're ready to configure the server.

2. Method 1: Configuring with Netplan (Ubuntu/Debian)

Modern Ubuntu Server editions use Netplan as the standard tool for network configuration. It uses simple text files written in YAML format to describe what the network configuration should be.

The video you just started watching provides a perfect walkthrough.

Let's review the key components of the Netplan file you created. It should look something like this:

A breakdown of the configuration:

• network:: The root of the file.
• ethernets:: Defines wired network interfaces.
• ens33:: Your interface name goes here.
• dhcp4: no: This is critical. It tells the system not to request an address from a DHCP server.
• addresses: [192.168.157.128/24]: Your chosen static IP and subnet mask go here. The brackets [] indicate a list, as you can assign multiple IPs to one interface.
• gateway4: 192.168.157.2: Your gateway address goes here. (Note: newer Netplan versions may use a routes section as shown in the video, which is also correct).
• nameservers:: Defines DNS servers. Using public DNS servers like Google's (8.8.8.8, 8.8.4.4) or Cloudflare's (1.1.1.1) is a safe bet.

After saving the file, sudo netplan apply reads this configuration and makes it active.

Verify your work with ip a to see the new address.

3. Method 2: Configuring with nmcli (Red Hat/CentOS)

While Netplan is the standard for Ubuntu Server, in the broader Linux world, especially in environments using Red Hat Enterprise Linux (RHEL) or its derivatives like CentOS, NetworkManager is the dominant force. Its command-line tool is nmcli. Knowing how to use it will make you more versatile.

This method is more procedural—you issue commands to modify a connection profile, rather than declaring the final state in a file.

Here is a summary of the nmcli process, which you can run on your VM (it will override your Netplan settings as long as NetworkManager is installed and running):

1. Find your connection name:
   nmcli connection show
   This will likely be named after your interface, e.g., Wired connection 1.

2. Modify the connection in a single command:
   Replace <NAME>, <IP/CIDR>, <GATEWAY>, and <DNS> with your details.

   sudo nmcli con mod "<NAME>" ipv4.method manual ipv4.addresses <IP/CIDR> ipv4.gateway <GATEWAY> ipv4.dns "8.8.8.8,1.1.1.1" connection.autoconnect yes
   

   For example:

   sudo nmcli con mod "Wired connection 1" ipv4.method manual ipv4.addresses 192.168.38.200/24 ipv4.gateway 192.168.38.2 ipv4.dns "8.8.8.8,1.1.1.1" connection.autoconnect yes
   

3. Apply the changes:
   sudo nmcli con up "<NAME>"

This sequence modifies the profile and then reapplies it, making the changes active. The connection.autoconnect yes part is crucial; it ensures NetworkManager brings this connection up automatically at boot.

4. Temporary vs. Persistent Configuration: A Key Concept

You might see examples online of people using ip addr add .... Why didn't we do that? Because those changes are temporary. They will be lost when you reboot the server or restart the networking service. For a server, this is unacceptable.

Using tools like Netplan or NetworkManager (nmcli) writes your configuration to files, ensuring it is persistent across reboots. This is a fundamental principle of system administration and a great point to bring up in an interview to show you understand the difference between a quick fix and a robust configuration.

Conclusion

You have now successfully configured a static IP address on a Linux server using two of the most common modern methods. This is a day-one skill for any data center technician or Linux administrator.

Key Takeaways:

• Servers require static IPs for reliability and predictability.
• The configuration process is: Gather Info -> Configure -> Apply -> Verify.
• Netplan is the declarative, YAML-based standard for modern Ubuntu Server.
• nmcli is the procedural, command-based tool for NetworkManager, common in the RHEL ecosystem.
• Always use a management tool (like Netplan or nmcli) to ensure your configuration is persistent. Avoid using ip addr add for permanent server setup.

In our next lesson, we will continue with essential system administration tasks by learning how to schedule recurring administrative jobs using cron. This will allow you to automate tasks like backups, updates, and system checks.