To Configure a network bridges in Linux is a common method of merging two or more network interfaces into a single virtual interface. Bridging can help improve network performance, ensure redundancy, and support load balancing. A network bridge allows a Linux system to share its internet connection with other devices, making it useful for scenarios like connecting a system without internet access to one with an active connection via Ethernet.
A network bridge operates at the Data Link Layer (Layer 2), forwarding traffic based on MAC addresses. Linux supports both hardware and software bridges, enabling hosts to act as transparent bridges between networks. The Linux kernel has included bridging support since versions 2.4 and 2.6, adhering partially to the ANSI/IEEE 802.1d standard.
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This tutorial will walk you through configuring a network bridge on various Linux distributions, such as Debian, Ubuntu, RHEL, and CentOS, using tools like brctl, iproute2, nmcli, and netplan.
1. Configuring a Network Bridge on Debian/Ubuntu with brctl
1.1 Installing the Network Bridge Utilities
To configure a network bridge on Debian or Ubuntu, you’ll need to install the bridge-utils package, which contains the brctl utility. Run the following command:
sudo apt install bridge-utilsThis tool allows you to create and manage virtual bridge interfaces.
Note: Ensure that your network cards are correctly installed and in the DOWN state before proceeding. Do not assign IP addresses or enable DHCP on any of the Ethernet interfaces until the bridge is fully configured.
1.2 Creating a Bridge Interface
Create a new bridge interface with:
sudo brctl addbr br0You can choose any name for the bridge interface, such as br0. To delete a bridge, use:
sudo brctl delbr br01.3 Adding Devices to the Bridge
To add Ethernet interfaces to the bridge:
sudo brctl addif br0 ens18 ens19This adds interfaces ens18 and ens19 to the br0 bridge.
1.4 Viewing Bridge Status
To view the current bridge status:
sudo brctl showTo see the MAC addresses of traffic being forwarded through the bridge:
sudo brctl showmacs br01.5 Configuring Permanent Bridging
To make the bridge configuration permanent, edit /etc/network/interfaces:
# The loopback network interface<br>auto lo<br>iface lo inet loopback<br><br># Set up interfaces manually<br>iface ens18 inet manual<br>iface ens19 inet manual<br><br># Bridge setup<br>iface br0 inet dhcp<br>bridge_ports ens18 ens19You can also configure a static IP address for the bridge:
iface br0 inet static
bridge_ports ens18 ens19
address 192.168.0.2
netmask 255.255.255.0
gateway 192.168.0.1Restart the networking service:
sudo systemctl restart networking2. Configuring a Network Bridge on RHEL/CentOS/AlmaLinux with brctl
2.1 Installing Bridge Utilities
Install the bridge-utils package on RHEL/CentOS/AlmaLinux:
sudo yum install bridge-utils2.2 Creating a Bridge Interface
Create a file named ifcfg-br0 in the /etc/sysconfig/network-scripts/ directory with the following configuration:
DEVICE=br0<br>TYPE=Bridge<br>IPADDR=192.168.0.2<br>NETMASK=255.255.255.0<br>ONBOOT=yes<br>NM_CONTROLLED=no<br>DELAY=02.3 Adding Interfaces to the Bridge
Configure the Ethernet interface with the following in ifcfg-ethX:
DEVICE=ethX<br>TYPE=Ethernet<br>ONBOOT=yes<br>NM_CONTROLLED=no<br>BRIDGE=br0Restart the network service:
sudo service network restart3. Configuring a Network Bridge on Linux with the ip Tool
3.1 Installing iproute2
On RHEL/CentOS/AlmaLinux:
sudo yum install iprouteOn Debian/Ubuntu:
sudo apt install iproute23.2 Creating a Bridge with ip
Create a new bridge:
sudo ip link add name br0 type bridge<br>sudo ip link set br0 upDelete a bridge:
sudo ip link delete br0 type bridge3.3 Adding Devices to the Bridge
To add devices to the bridge:
sudo ip link set ens18 master br0<br>sudo ip link set ens19 master br03.4 Viewing Bridge Status
View the bridge status:
bridge link4. Configuring a Network Bridge on Linux with nmcli
4.1 Creating a Bridge with nmcli
To create a new bridge:
sudo nmcli connection add type bridge con-name bridge0 ifname br04.2 Adding Devices to the Bridge
Add Ethernet interfaces to the bridge:
sudo nmcli con add type ethernet slave-type bridge con-name bridge0-port0 ifname ens18 master br0<br>sudo nmcli con add type ethernet slave-type bridge con-name bridge0-port1 ifname ens19 master br0Bring up the bridge:
sudo nmcli con up br04.3 Setting a Static IP for the Bridge
Assign a static IP to the bridge:
sudo nmcli connection modify br0 ipv4.addresses 192.168.0.2/24
sudo nmcli connection modify br0 ipv4.gateway 192.168.0.14.4 Viewing Bridge Status
To check the bridge status:
nmcli device showIf you follow this guide step by step, you can configure a network bridge on various Linux distributions, using tools like brctl, ip, nmcli, and others. Bridging can be a powerful way to manage your network and increase flexibility across interfaces.
