How to resolve IP conflicts on Ubuntu Server clones

If you've ever cloned a Ubuntu Server VM on a DHCP network, you'll notice that they try to occupy the same address even though their MAC addresses are different. This guide explains how to resolve this conflict for Ubuntu Server versions 18.04–24.04.

Cause

Since 18.04, Ubuntu Server has used Netplan instead of NetworkManager
Out of the box, Netplan uses the dhcp-identifier option to register itself with the DHCP server
On Ubuntu, the default behaviour is to fall back to the IPv6 DUID (DHCP Unique Identifier), which is stored in /var/lib/dbus/machine-id and /etc/machine-id
Because the machine ID persists when the VM is cloned, it causes conflicts

Resolution

To fix the issue, you can instruct Netplan to use MAC addresses instead of DUID.

Edit /etc/netplan/50-cloud-init.yaml, and add dhcp-identifier: mac:

network:
    ethernet:
        enp1s0: # This will vary by interface name
            dhcp4: true
            dhcp-identifier: mac # Add this line

Apply the configuration:
```
sudo netplan apply
```
Request a new address via DHCP:
```
sudo dhclient -r
sudo dhclient
```

There are other solutions that will work. For example, you could edit the DUID at /etc/machine-id to a unique value, preventing the conflict. However, the method in this guide works just as well.