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Ubuntu Network Configuration

Basic network configuration for Ubuntu systems

0. Specs

0.0. Info

Network configuration examples on Ubuntu 24.04 LTS and 26.04 LTS Servers.

Tried to be as thorough as possible: single NIC, multiple NICs, multiple networks.

Debian and Ubuntu network configurations are very different, so there are separate tutorials for Debian and Ubuntu.

0.1. Configuration Files

Ubuntu 24.04 and 26.04 LTS Servers use Systemd-Networkd and Netplan for network configuration.

Configuration files reside as YAML files in the /etc/netplan directory. A good practice is to have one configuration file there.

This configuration file contains all network configurations, including name servers.

0.2. Sources


1. Example Configurations

1.1. DHCP Configuration

Our NIC is enp0s3.

Edit configuration file. Yours might be named something else, in that case, edit that file.

sudo nano /etc/netplan/50-cloud-init.yaml

Fill as below:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      dhcp4: true

sudo netplan apply

1.2. Static IP Configuration

Our NIC is enp0s3.

sudo nano /etc/netplan/50-cloud-init.yaml

Fill as below:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      addresses:
        - 192.168.1.226/24
      nameservers:
        search:
          - "x386.org"
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      routes:
        - to: default
          via: 192.168.1.1

sudo netplan apply

1.3. Static IP Configuration with 2 IPs

Our NIC is enp0s3.

sudo nano /etc/netplan/50-cloud-init.yaml

Fill as below:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      addresses:
        - 192.168.1.226/24
        - 10.1.1.1/8
      nameservers:
        search:
          - "x386.org"
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      routes:
        - to: default
          via: 192.168.1.1

sudo netplan apply

1.4. Static IP Configuration with 2 NICs

Our NICs are enp0s3 and enp0s8.

sudo nano /etc/netplan/50-cloud-init.yaml

Fill as below:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      addresses:
        - 192.168.1.226/24
      nameservers:
        search:
          - "x386.org"
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      routes:
        - to: default
          via: 192.168.1.1
    enp0s8:
      addresses:
        - 10.1.1.1/8

sudo netplan apply


2. Case Study - Multiple Networks

2.0. Specs

We have 2 separate networks (192.168.1.X and 10.X.X.X). Some hosts from one network need to reach hosts in the other network.

We will install a new host to act as a router between the networks.

The host will have 2 NICs (one in each network), and we'll enable IP routing on it.

This way, hosts in one network will be able to reach hosts in the other network. This will be possible by defining IP routes on the hosts to use the server with 2 NICs as a router to the other network.

Hosts in the 192.168.1.X network use 192.168.1.1 as the default gateway; hosts in the 10.X.X.X network use 10.1.1.1 as the default gateway.

Our router will have 2 NICs: one with IP 192.168.1.226 and the other with IP 10.1.1.226.

Hosts in the 192.168.1.X network will use 192.168.1.226 to reach the 10.X.X.X network. Hosts in the 10.X.X.X network will use 10.1.1.226 to reach the 192.168.1.X network.

We will configure:

  • The router (192.168.1.226 & 10.1.1.226)
  • The host in the first network (192.168.1.227)
  • The host in the second network (10.1.1.228)

Then we'll check connectivity between them.

2.1. Configuration of the Router

We have 2 NICs (enp0s3 - 192.168.1.X network, and enp0s8 - 10.X.X.X network).

Configure NICs: - enp0s3: 192.168.1.226/24 - enp0s8: 10.1.1.226/8

sudo nano /etc/netplan/50-cloud-init.yaml

Fill as below:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      addresses:
        - 192.168.1.226/24
      nameservers:
        search:
          - "x386.org"
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      routes:
        - to: default
          via: 192.168.1.1
    enp0s8:
      addresses:
        - 10.1.1.226/8

Restart networking (your SSH connection may break; reconnect if needed):

sudo netplan apply

Enable IP forwarding:

sudo nano /etc/sysctl.conf

Add the following line to the end:

net.ipv4.ip_forward = 1

Activate:

sudo sysctl -p

2.2. Configuration of the First Host

We have 1 NIC (enp0s3 - 192.168.1.X network).

sudo nano /etc/netplan/50-cloud-init.yaml

Fill as below:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      addresses:
        - 192.168.1.227/24
      nameservers:
        search:
          - "x386.org"
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      routes:
        - to: default
          via: 192.168.1.1
        - to: 10.0.0.0/8
          via: 192.168.1.226

Restart networking (your SSH connection may break; reconnect if needed):

sudo netplan apply

2.3. Configuration of the Second Host

We have 1 NIC (enp0s3 - 192.168.1.X network).

sudo nano /etc/netplan/50-cloud-init.yaml

Fill as below:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      addresses:
        - 10.1.1.228/8
      nameservers:
        search:
          - "x386.org"
        addresses:
          - 8.8.8.8
          - 8.8.4.4
      routes:
        - to: default
          via: 10.1.1.1
        - to: 192.168.1.0/24
          via: 10.1.1.226

Restart networking (your SSH connection may break; reconnect if needed):

sudo netplan apply

2.4. Notes

The host in the first network can ping the host in the other network now, and vice versa.

Try on the first host (192.168.1.227)

ping 10.1.1.228

Try on the second host (10.1.1.228)

ping 192.168.1.227

For a host to connect to another host on the other network, routing must be defined on both hosts.


3. NIC Bonding

I tried NIC bonding on Ubuntu, but unfortunately I wasn't successful.

This might be because of VirtualBox, Netplan, or Networkd. So I gave up. Maybe next time.

I was able to create the bond interface, and it got an IP address too, but it could not connect to anywhere on the network. Even working with Networkd directly didn't help.

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