Upgrading Ubuntu 24.04 Network Configuration

Debian/Ubuntu and RHEL/AlmaLinux have different network configuration utilities. RHEL 9 has deprecated ifcfg-files, and adopted NetworkManager. There is no ifup or ifdown any more after a fresh installation. Since my server was first installed using Ubuntu 14.04, it still uses these scripts. Time to move on.

1. ifupdown

Netplan is used to configure networking in Ubuntu 18.04 and later. Ubuntu Server is packaged with systemd-networkd as the backend for Netplan, while NetworkManager is used as the Netplan backend in Ubuntu Desktop. Install by:

# sudo apt-get install netplan.io

1	# sudo apt-get install netplan.io

Get current network status by:

# sudo netplan status
...
●  1: lo ethernet UNKNOWN/UP (unmanaged)
      MAC Address: 00:00:00:00:00:00
...
●  3: eth0 ethernet UP (unmanaged)
      MAC Address: f2:3c:91:6e:3b:e1 (Red Hat, Inc.)
...

# sudo netplan status

...

● 1: lo ethernet UNKNOWN/UP (unmanaged)

MAC Address: 00:00:00:00:00:00

...

● 3: eth0 ethernet UP (unmanaged)

MAC Address: f2:3c:91:6e:3b:e1 (Red Hat, Inc.)

...

eth0 is unmanaged, since ifupdown is used. The config file is /etc/network/interfaces.

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

# This file describes the network interfaces available on your system

# and how to activate them. For more information, see interfaces(5).

# The loopback network interface

auto lo

iface lo inet loopback

# The primary network interface

auto eth0

iface eth0 inet dhcp

2. networkd

Create a config file /etc/netplan/50-cloud-init.yaml

network:
  version: 2
  ethernets:
    eth0:
      dhcp4: true

network:

version: 2

ethernets:

eth0:

dhcp4: true

This file is create by cloud-init if fresh installed. I kept the name. networkd comes with systemd, no need to install it again. Apply it by:

# sudo netplan generate
# sudo netplan try

1 2	# sudo netplan generate # sudo netplan try

Now, eth0 should be managed by networkd:

# sudo netplan status
...
●  1: lo ethernet UNKNOWN/UP (unmanaged)
      MAC Address: 00:00:00:00:00:00
...
●  3: eth0 ethernet UP (networkd: eth0)
      MAC Address: f2:3c:91:6e:3b:e1 (Red Hat, Inc.)
...

# sudo netplan status

...

● 1: lo ethernet UNKNOWN/UP (unmanaged)

MAC Address: 00:00:00:00:00:00

...

● 3: eth0 ethernet UP (networkd: eth0)

MAC Address: f2:3c:91:6e:3b:e1 (Red Hat, Inc.)

...

The generated config file can be found in /run/systemd/network/10-netplan-eth0.network. System config files located in /etc/systemd/networkd.conf & /usr/lib/systemd/network/.

3. NetworkManager

NetworkManager can also be used for servers. Install by:

# sudo apt-get install network-manager network-manager-config-connectivity-ubuntu

1	# sudo apt-get install network-manager network-manager-config-connectivity-ubuntu

Create a config file /etc/netplan/01-network-manager-all.yaml.

# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager

# Let NetworkManager manage all devices on this system

network:

version: 2

renderer: NetworkManager

This file is create by Ubuntu installer if fresh installed. I kept the name. Verify the merged config by running:

# sudo netplan get
network:
  version: 2
  renderer: NetworkManager
  ethernets:
    eth0:
      dhcp4: true

# sudo netplan get

network:

version: 2

renderer: NetworkManager

ethernets:

eth0:

dhcp4: true

NOTE, one additional step need to be performed, /etc/network/interfaces must *not* exist. NetworkManager has a plugin to parse the file. Backup it, so that you can roll back to ifupdown if something goes wrong. Apply it by:

# sudo netplan generate
# sudo netplan try

1 2	# sudo netplan generate # sudo netplan try

Now, eth0 should be managed by NetworManager:

# sudo netplan status
...
●  1: lo ethernet UNKNOWN/UP (unmanaged)
      MAC Address: 00:00:00:00:00:00
...
●  3: eth0 ethernet UP (NetworManager: eth0)
      MAC Address: f2:3c:91:6e:3b:e1 (Red Hat, Inc.)
...

# sudo netplan status

...

● 1: lo ethernet UNKNOWN/UP (unmanaged)

MAC Address: 00:00:00:00:00:00

...

● 3: eth0 ethernet UP (NetworManager: eth0)

MAC Address: f2:3c:91:6e:3b:e1 (Red Hat, Inc.)

...

The generated config file can be found in /run/NetworkManager/system-connections/netplan-eth0.nmconnection. System config files located in /etc/NetworkManager/NetworkManager.conf & /usr/lib/NetworkManager/. On systems before RHEL 9, /run may be /var/run. When NetworkManager starts and finds no connection for a device it might create an in-memory connection. No config file is created. The no-auto-default configuration disables that behavior. Check systemd log for details:

# sudo journalctl -u NetworkManager
...
ifcfg-rh: add connection in-memory (a05d8c6f-fa6f-34c9-bee0-09b029470893,"Wired connection 1")
...

# sudo journalctl -u NetworkManager

...

ifcfg-rh: add connection in-memory (a05d8c6f-fa6f-34c9-bee0-09b029470893,"Wired connection 1")

...

More info can be found in Debian documents. Useful commands include: NetworkManager --print-config, nmcli device & nmcli connection.

4. Clean ups

Now, you can safely remove ifupdown, and the networking systemd service will be removed too.

# sudo apt-get purge ifupdown

1	# sudo apt-get purge ifupdown

5. iptables

An ifupdown script was add to persist iptables rules.

# cat /etc/network/if-pre-up.d/firewall 
sudo /usr/sbin/iptables-restore < /etc/iptables.firewall.rules

1 2	# cat /etc/network/if-pre-up.d/firewall sudo /usr/sbin/iptables-restore < /etc/iptables.firewall.rules

This can be migrated by installing iptables-persistent:

# sudo apt-get install iptables-persistent

1	# sudo apt-get install iptables-persistent

1. ifupdown

2. networkd

3. NetworkManager

4. Clean ups

5. iptables

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