How to Set Up Static IP Address and Custom Routing on Ubuntu: The Complete Guide

Configuring a static IP address and custom routes is an essential skill for anyone managing Ubuntu servers, workstations, or cloud instances. This comprehensive guide will walk you through every step of the process, explain key concepts behind network routing, and provide troubleshooting tips to ensure your configuration is robust and reliable.

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Why Configure a Static IP and Custom Routes?

• Static IP: Ensures your system always has the same address, which is crucial for remote access, web hosting, and network services.

• Custom Routes: Control how traffic moves through your network, optimize connections, or access specific remote hosts.

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Step 1: Identify Your Network Interface

The first step is to determine which network interface you want to configure. Interface names on Ubuntu can be eth0, ens3, enp0s3, etc.

ip link show

Look for an interface that is UP and connected. Example output:

2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 ...

Here, ens3 is our interface.

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Step 2: Prepare Your Static IP Details

Before configuring, gather the following information (using demo values):

• IP Address: 192.0.2.10

• Subnet Mask/CIDR: /24

• Gateway: 192.0.2.1

• DNS Server(s): 8.8.8.8 (Google Public DNS)

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Step 3: Configure Netplan (Ubuntu 18.04+)

Ubuntu uses Netplan for network configuration. Netplan files are found in /etc/netplan/. List them:

ls /etc/netplan/

Open the appropriate file (e.g., 01-netcfg.yaml) for editing:

sudo nano /etc/netplan/01-netcfg.yaml

Add or update with your configuration (using demo IPs):

network:
  version: 2
  ethernets:
    ens3:
      dhcp4: no
      addresses:
        - 192.0.2.10/24
      gateway4: 192.0.2.1
      nameservers:
        addresses: [8.8.8.8]
      routes:
        - to: 192.0.2.1/32
          scope: link
          via: 0.0.0.0
          on-link: true
        - to: default
          via: 192.0.2.1
          on-link: true

Explanation:

• dhcp4: no: Disables DHCP, enables static IP.

• addresses: Sets the IP and subnet mask.

• gateway4: Sets the gateway for outbound traffic.

• nameservers: DNS servers for resolving domain names.

• routes:

  • to: Destination for the route (single IP or default).

  • scope: link means route is directly reachable on the local interface.

  • via: Next hop; 0.0.0.0 means direct, no gateway.

  • on-link: Tells the system this address is directly reachable.

  • default route: For all traffic not matched by other routes, use the specified gateway.

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Step 4: Apply Your Configuration

Run the following to activate your changes:

sudo netplan apply

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Step 5: Verify Your Network Configuration

Check your IP address:

ip a

Check your routing table:

ip route

Sample output:

192.0.2.1 dev ens3  scope link
default via 192.0.2.1 dev ens3

Check your DNS:

cat /etc/resolv.conf

Test connectivity:

ping -c 4 8.8.8.8
ping -c 4 example.com

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Understanding Routes in Detail

What is a Route?

A route tells your system how to reach networks or hosts. The routing table contains rules that determine which interface and gateway traffic uses.

Key Route Fields

• scope: link: The destination is directly reachable on the local network (no gateway needed).

• to: The target IP or network (e.g., 192.0.2.1/32 for one host, or default for all traffic).

• via: The next hop (gateway) for reaching the destination. 0.0.0.0 means direct (no gateway).

• on-link: Marks the destination as directly reachable on the local segment.

Example 1: Link-Scoped Route

- to: 192.0.2.1/32
  scope: link
  via: 0.0.0.0
  on-link: true

• Packets destined for 192.0.2.1 are sent directly via ens3, with no gateway.

Example 2: Default Route

- to: default
  via: 192.0.2.1
  on-link: true

• All traffic not matching a more specific rule goes to the gateway 192.0.2.1.

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Summary Table: Route Fields

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Visual Example (Routing Table)

Imagine your routing table looks like this:

Destination        Gateway         Genmask         Flags Iface
192.0.2.1          0.0.0.0         255.255.255.255 UGH   ens3
0.0.0.0            192.0.2.1       0.0.0.0         UG    ens3

• First row: Direct route to 192.0.2.1 via ens3 (no gateway).

• Second row: Default route—send everything else via 192.0.2.1.

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Troubleshooting

• Network unreachable: Double-check IP, gateway, and interface name.

• YAML errors: Make sure you use spaces (not tabs) and correct indentation in Netplan files.

• DNS not working: Some systems may overwrite /etc/resolv.conf. Use Netplan to set DNS or configure systemd-resolved.

• Connectivity issues: Use ip a, ip route, and ping to diagnose.

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Advanced: Temporary Network Changes (No Reboot Needed)

If you want to test settings without editing Netplan, use these commands (using demo IPs):

sudo ip addr flush dev ens3
sudo ip addr add 192.0.2.10/24 dev ens3
sudo ip link set ens3 up
sudo ip route add 192.0.2.1 dev ens3
sudo ip route add default via 192.0.2.1
echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

Note: These changes are lost after reboot.

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Conclusion

Configuring a static IP address and custom routes on Ubuntu is straightforward once you understand the concepts and configuration syntax. Whether you’re running a server, a cloud VM, or a desktop, these steps ensure your system is reliably reachable and communicates efficiently on your network.

Key Takeaways:

• Know your network interface name.

• Use Netplan for permanent configuration.

• Understand how routes work—especially link scope and default routes.

• Test and verify your setup for reliability.

Have questions or want to learn more about advanced routing? Comment below or explore Ubuntu’s official networking documentation!