Upgrading Ubuntu 20.x -> 22.x killed my network

So the answer above didn’t work for me. What I ended up doing was creating a new YAML file at /etc/netplan/config.yaml with the following content:

network:
  version: 2
  renderer: networkd
  ethernets:
      eth0:
          addresses: [ "<droplet IP address>/24" ]
          routes:
            - to: default
              via: <droplet gateway IP address>
              on-link: true #only needed if the droplet is on a different subnet

If your droplet gateway is on a different subnet (i.e. more than just the last set of numbers in the IP address and gateway IP address are different), you need to include the “on-link” line.

Save the file and then run this command:

netplan generate

followed by

netplan apply

That will set the static IP and gateway address and make it persist past reboots.

If you need to temporarily add the static IP address and gateway, use these commands:

ip addr add <droplet IP address> dev eth0
ip link set dev eth0 up
ip route add default via <gateway IP address> onlink dev eth0

This will give you connectivity in order to run updates and install additional packages, but that connectivity will not persist on reboot.

I hope this helps someone.

In my case the issue was caused by the fact that eth0 was replaced by ens0. In order to check what your card name is :

ll /sys/class/net/
total 0
drwxr-xr-x  2 root root 0 set 26 08:46 ./
drwxr-xr-x 70 root root 0 set 26 08:46 ../
lrwxrwxrwx  1 root root 0 set 26 08:49 docker0 -> ../../devices/virtual/net/docker0/
lrwxrwxrwx  1 root root 0 set 26 08:46 ens3 -> ../../devices/pci0000:00/0000:00:03.0/virtio1/net/ens3/
lrwxrwxrwx  1 root root 0 set 26 08:46 lo -> ../../devices/virtual/net/lo/
lrwxrwxrwx  1 root root 0 set 26 08:49 veth0210b8e -> ../../devices/virtual/net/veth0210b8e/

as you can see I have no eth0 but I have a “suspicious” ens3.

Cross reference the findings with what’s inside /etc/network/interfaces.d/50-cloud-init.cfg

auto eth0
iface eth0 inet static
    address <your ip>
    dns-nameservers 8.8.8.8 8.8.4.4
    gateway <your gateway>
    netmask 255.255.192.0
    post-up ifup eth0:1


auto eth0:1
iface eth0:1 inet static
    address <your ip>
    netmask 255.255.0.0

At that point I changed the occurrences of eth0 with ens3 in cloud-init.cfg and tried to manually up/down my network :

ifdown eth0
ip addr flush dev eth0
ip addr flush dev ens3
ifup ens3

ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=117 time=2.96 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=117 time=0.853 ms

nslookup google.com
Server:		127.0.0.53
Address:	127.0.0.53#53

Non-authoritative answer:
Name:	google.com
Address: 142.250.179.174
Name:	google.com
Address: 2a00:1450:400e:811::200e

all up and running.

Reboot

njoy :)