Creating a Linux Network Bridge on CentOS 8 / RHEL 8 using nmcli

Network bridge behaves as a virtual network switch. We’ll proceed further to see how it can be created and used follow the below steps to get started.

Step 1: Creating a Linux Bridge

Here we will use the nmcli network management command line tool to create a Linux bridge on a desired interface.

To see connections available run the following command.

$ sudo nmcli connection show
NAME        UUID                                  TYPE      DEVICE     
 ens33       8806158c-9c2b-4ffb-8109-8b662baf8581  ethernet  ens33      
 virbr0      06282371-27ba-4f03-b3c5-ebcc401e2531  bridge    virbr0     
 virbr0-nic  0dcb669a-5ead-4a67-a877-2f78d432691e  tun       virbr0-nic 
 ens33       93392eb5-c75b-45ea-80a3-509e01144dc7  ethernet  --         
 ens33       2a10fc64-1312-4232-8103-5cdc114cf5b8  ethernet  --         

As my bridge will be created on the second device ens33 So, I’ll delete the existing connection to create a bridge connection with this device.

$ sudo nmcli connection delete ens33
[sabi@localhost root]$ sudo nmcli connection delete ens33
Connection 'ens33' (93392eb5-c75b-45ea-80a3-509e01144dc7) successfully deleted.
Connection 'ens33' (2a10fc64-1312-4232-8103-5cdc114cf5b8) successfully deleted.
Connection 'ens33' (8806158c-9c2b-4ffb-8109-8b662baf8581) successfully deleted.

Now save bridge related information to variables.

BR_NAME="ifname"
BR_INT="ens29"
SUBNET_IP="192.168.94.10/24"
GW="192.168.94.1"
DNS1="8.8.8.8"
DNS2="8.8.4.4"

• BR_NAME: Name of the bridge, we are going to create.
• BR_INT: Physical device to be used as a bridge slave.
• SUBNET_IP: IP address & subnet assigned to the created bridge.
• GW: Default Gateway address.
• DNS1 & DNS2: DNS servers IP which are to be used.

Now after assigning information, create new bridge connection.

sudo nmcli connection add type bridge autoconnect yes con-name ${BR_NAME} ifname ${BR_NAME}

You will see the following output upon successful creation.

Connection 'ifname' (f76df2f2-f4ed-48a3-b39d-e58979710298) successfully added.

After creating connection of bridge assign the IP address, Gateway and DNS servers.

sudo nmcli connection modify ${BR_NAME} ipv4.addresses ${SUBNET_IP} ipv4.method manual
sudo nmcli connection modify ${BR_NAME} ipv4.gateway ${GW}
sudo nmcli connection modify ${BR_NAME} ipv4.dns ${DNS1} +ipv4.dns ${DNS2}

Now add the network device as a bridge slave.

sudo nmcli connection delete ${BR_INT}
sudo nmcli connection add type bridge-slave autoconnect yes con-name ${BR_INT} ifname ${BR_INT} master ${BR_NAME}

Output:

Connection 'ifname' (f76df2f2-f4ed-48a3-b39d-e58979710298) successfully added.

Run the following command to check connection changes.

sudo nmcli connection show

You’ll see the bridge connection you’ve just created.

NAME        UUID                                  TYPE      DEVICE
ens33       dde2beed-2e9d-4ea8-82c6-460306f17847  ethernet  ens33      
virbr0      06282371-27ba-4f03-b3c5-ebcc401e2531  bridge    virbr0     
virbr0-nic  0dcb669a-5ead-4a67-a877-2f78d432691e  tun       virbr0-nic 
ifname      f76df2f2-f4ed-48a3-b39d-e58979710298  bridge    nm-bridge  
ifname      984edc85-9e75-45b1-843b-e06d11631cae  bridge    nm-bridge1 

Step 2: Bring up Network Bridge

Now it’s time to bring up the network bridge after creating successful connection.

sudo nmcli connection up ifname
Connection successfully activated (master waiting for slaves) (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/5)

You can view bridge details by running

sudo nmcli connection show ifname

To find out IP address run the following command .

$ ip ad

That’s it! The bridge is now ready to use.

If have any queries regarding this tutorial, feel free to ask!

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