Add br0 to Ubuntu desktop using nmcli

addbr0ubunmcli.md

Add a bridge interface to Ubuntu desktop using nmcli

Had to do this for some advanced networking with KVM, and couldn't figure out how to do it using the Nework Manager gui. Did find an article later that showed how to do it with nmtui, but it's so much easier to record what you did when using the cli.

In the examples below "eth0" is the name of my physical interface. By default on Ubuntu and most distributions that will almost certainly be different, for example: "eno1", "ens1", or "enp2s0".

To see what everything looks like before starting:

$ nmcli con show

I renamed "Wired Connection 1' to the name of my physical interface:

$ sudo nmcli con mod 'Wired Connection 1' con-name eth0

So let's start out by creating the bridge itself:

$ nmcli con add ifname br0 type bridge con-name br0

Now add the physical interface as its slave:

$ nmcli con add type bridge-slave ifname eth0 master br0

Disable STP:

$ nmcli con mod br0 bridge.stp no

Now down the physical interface:

$ nmcli con down eth0

For this machine I want a static address:

$ nmcli con mod br0 ipv4.addresses 10.1.1.16/24
$ nmcli con mod br0 ipv4.gateway 10.1.1.1
$ nmcli con mod br0 ipv4.dns '10.1.1.1,8.8.8.8,8.8.4.4'

Don't forget to set your search domain:

$ nmcli con mod br0 ipv4.dns-search 'example.com'

Then tell Network Manager this will be a manual connection:

$ nmcli con mod br0 ipv4.method manual

Finally, bring up the new bridge interface:

$ nmcli con up br0

Run nmcli device show to confirm your changes, and then restart NetworkManager (sudo systemctl restart NetworkManager.service) to make sure the configuration sticks.

hi, im trying to follow your steps to create the bridge and everything seems ok until i try to turn the br0 to up. i get this error message:
"Error: Connection activation failed: Connection 'br0' is not available on device br0 because device is strictly unmanaged" i have googled a bit of course and tried a few things but still cannot bring it up , what am i missing ? any suggestions ? thanks

PRETTY_NAME="Ubuntu 22.04.4 LTS"
NAME="Ubuntu"
VERSION_ID="22.04"
VERSION="22.04.4 LTS (Jammy Jellyfish)"
VERSION_CODENAME=jammy
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=jammy

thanks,

Can you provide the output of ip addr, nmcli con show and nmcli con show br0 ?

hi, im trying to follow your steps to create the bridge and everything seems ok until i try to turn the br0 to up. i get this error message: "Error: Connection activation failed: Connection 'br0' is not available on device br0 because device is strictly unmanaged" i have googled a bit of course and tried a few things but still cannot bring it up , what am i missing ? any suggestions ? thanks

Google actually knows the answer to your problem but finding it depends... Switching over to network-manager needs a bit of work before it can be used. I'll try to summarize the steps needed:

• install network-manager ( apt install network-manager )
• remove netplan that comes with Ubuntu by default. Do apt search netplan , then do apt purge to all those that come up as installed ( along the lines of apt purge netplan.io libnetplan0 )
• apt autoremove to get rid of remaining orphaned stuff
• edit /etc/NetworkManager/NetworkManager.conf file. There's [ifupdown] section, set managed=true
• do touch /etc/NetworkManager/conf.d/10-globally-managed-devices.conf , this creates empty file and overrides settings in the same named file in /usr/lib/NetworkManager/conf.d directory
• check if /etc/network/interfaces file is empty/comments only
• (re)start network-manager ( systemctl start NetworkManager ), see if nmcli behaves any different
• it may require restart (and prayer) that there's nothing else hindering nmcli now.

I haven't tried removing netplan from Desktop before (on Desktop it ships configured to give Network Manager control over all network devices, while it gives control to systemd-networkd on Server). I'd be interested to hear if removing netplan entirely cleaned up the "strictly unmanaged" error b3to is experiencing.