Best Network Bridge Configuration on Debian 12 Linux

This guide aims to teach you Network Bridge Configuration on Debian 12 Linux. First, we will describe what a network bridge is and then delve into the network configuration and creation of a bridge on Debian 12 Bookworm. Please follow the rest of the article to successfully complete the Network Bridge Configuration on Debian 12 Linux.

What is a Network Bridge on Linux?

In simple terms, a network bridge is a device that divides a network into segments. Each segment represents a separate collision domain, so the number of collisions on the network is reduced. Each collision domain has its own separate bandwidth, so a bridge also improves network performance.

How Does Network Bridge Work?

A bridge works at the Data link layer (Layer 2) of the OSI model. It inspects incoming traffic and decides whether to forward it or filter it. Each incoming Ethernet frame is inspected for the destination MAC address. If the bridge determines that the destination host is on another segment of the network, it forwards the frame to that segment.

To create a network bridge on your Debian 12, you must have access to your server as a non-root user with sudo privileges. To do this, you can follow this guide on Initial Server Setup with Debian 12 Bookworm.

Then, follow the steps below to complete Network Bridge Configuration on Debian 12 Linux.

Step 1 – Install the bridge-utils package on Debian 12 Linux

First, you must run the system update by using the following command:

sudo apt update

The bridge-utils package contains a utility needed to create and manage bridge devices.

Then, use the following command to install the bridge-utils on Debian 12:

sudo apt install bridge-utils -y

Now you need to make some configuration changes at the /etc/network/interface file.

Step 2 – Edit Network Configuration File on Debian 12

At this point, you must edit the network configuration file on your Debian 12 Linux server.

First, find your physical interface with the command below:

sudo ip -f inet a s

**Output**
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
inet ... brd ... scope global eth0
valid_lft forever preferred_lft forever

In my case, eth0 is my physical interface.

At this point of Network Bridge Configuration on Debian 12 Linux, you need to be sure that only “lo” (loopback) is active in the /etc/network/ interface.

Open the file with your favorite text editor, here we use the vi editor:

sudo vi /etc/network/interfaces

Remove any config related to eth0 and your config file should be similar to this:

When you are done, save and close the file.

Step 3 – Create a Bridge on Debian 12

Now create a file for your bridge on Debian 12 with your favorite text editor, here we use vi:

sudo vi /etc/network/interfaces.d/br0

Add the following content to your file:

## static ip config file for br0 ##
auto br0
iface br0 inet static
    address 192.168.2.23
    broadcast 192.168.2.255
    netmask 255.255.255.0
    gateway 192.168.2.254
    # If the resolvconf package is installed, you should not edit 
    # the resolv.conf configuration file manually. Set name server here
    #dns-nameservers 192.168.2.254
    # If you have muliple interfaces such as eth0 and eth1
    # bridge_ports eth0 eth1  
    bridge_ports eth0
    bridge_stp off       # disable Spanning Tree Protocol
    bridge_waitport 0    # no delay before a port becomes available
    bridge_fd 0          # no forwarding delay

Note: Remember to replace the address, broadcast, netmask, gateway, and bridge ports values.

When you are done, save and close the file.

Note: If you want a bridge to get an IP address using DHCP on Debian 12, add the following content to the file instead:

## DHCP ip config file for br0 ##
auto br0

# Bridge setup
 iface br0 inet dhcp
    bridge_ports eth0

Step 4 – Restart Network on Debian 12

Now you need to restart the network service. Before you restart the networking service make sure the firewall is disabled.

Use the command below to restart your service:

sudo systemctl restart networking

Then, verify that the service is started:

sudo systemctl status networking

Step 5 – Debian Linux brctl Command

At this point of Network Bridge Configuration on Debian 12 Linux, you can use the brctl command to view info about your bridges:

brctl show

Also, use the command below to show your current bridges:

bridge link

Alternative Solutions for Network Bridge Configuration on Debian 12 Linux

While the above method using bridge-utils and manual configuration files is a standard approach, there are alternative ways to achieve Network Bridge Configuration on Debian 12 Linux, offering potentially simpler or more automated solutions. Here are two alternative solutions:

1. Using `netplan`

netplan is a network configuration abstraction used by default in recent Ubuntu versions, and can be installed and used on Debian as well. It uses YAML files to define network configurations, which are then interpreted by a backend (usually NetworkManager or systemd-networkd). This approach can be simpler to manage for complex configurations and offers a more declarative approach.

Steps:

Install netplan and a network renderer (if not already present):
```
sudo apt update
sudo apt install netplan.io networkd
```
Note: Choose either networkd or NetworkManager as your renderer. networkd is lighter and suitable for servers.
Create or modify a netplan configuration file:

Netplan configuration files are located in /etc/netplan/. Create a new file (e.g., 01-network-config.yaml) or modify the existing one. Make sure the file ends with .yaml.

Example configuration for a static IP bridge:
```
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: no
  bridges:
    br0:
      interfaces: [eth0]
      dhcp4: no
      addresses: [192.168.2.23/24]
      gateway4: 192.168.2.254
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
```
- version: 2 specifies the netplan configuration version.
- renderer: networkd specifies the backend to use.
- ethernets: Defines the physical interface eth0 and disables DHCP.
- bridges: Defines the bridge interface br0.
- interfaces: Lists the physical interfaces to be part of the bridge.
- dhcp4: no disables DHCP on the bridge.
- addresses: Sets the static IP address and subnet mask for the bridge.
- gateway4: Sets the gateway for the bridge.
- nameservers: Sets the DNS servers.
For a DHCP-configured bridge:
```
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: no
  bridges:
    br0:
      interfaces: [eth0]
      dhcp4: yes
```
Apply the netplan configuration:
```
sudo netplan apply
```
This command will apply the configuration. If there are errors, it will report them.
Verify the configuration:

Use ip addr show br0 to verify that the bridge has been created and configured correctly.

Explanation:

netplan provides a higher-level abstraction for network configuration. Instead of directly manipulating /etc/network/interfaces, you define the desired state in a YAML file. The netplan apply command then translates this configuration into the necessary commands for the chosen backend (e.g., systemd-networkd) to configure the network interfaces. This approach can be easier to manage and more readable, especially for complex network setups.

2. Using `nmcli` (NetworkManager Command-Line Interface)

If you are using NetworkManager, you can use the nmcli command-line tool to create and manage network bridges. This is especially useful in desktop environments where NetworkManager is already managing network connections.

Steps:

Ensure NetworkManager is running:
```
sudo systemctl status NetworkManager
```
Create the bridge connection:
```
sudo nmcli con add type bridge con-name br0 ifname br0 stp no
```
- type bridge: Specifies the connection type as a bridge.
- con-name br0: Sets the connection name to br0.
- ifname br0: Sets the interface name to br0.
- stp no: Disables Spanning Tree Protocol.
Add the physical interface to the bridge:
```
sudo nmcli con add type ethernet slave master br0 con-name eth0 ifname eth0
```
- type ethernet: Specifies the connection type as ethernet.
- slave master br0: Makes eth0 a slave of the bridge br0.
- con-name eth0: Sets the connection name (can be the same as the interface name).
- ifname eth0: Sets the interface name to eth0.
Configure the bridge IP address (static example):
```
sudo nmcli con mod br0 ipv4.addresses 192.168.2.23/24 ipv4.gateway 192.168.2.254 ipv4.dns "8.8.8.8,8.8.4.4" ipv4.method manual
```
- ipv4.addresses: Sets the static IP address and subnet mask.
- ipv4.gateway: Sets the gateway.
- ipv4.dns: Sets the DNS servers.
- ipv4.method manual: Specifies manual IP configuration.
For DHCP configuration:
```
sudo nmcli con mod br0 ipv4.method auto
```

Activate the connections:

sudo nmcli con up br0
sudo nmcli con up eth0 # if the ethernet connection was previously down.

Verify the configuration:

Use ip addr show br0 or nmcli con show br0 to verify the configuration.

Explanation:

nmcli allows you to manage network connections through the NetworkManager service. By creating bridge and ethernet connections and linking them together, you can achieve the same result as the manual configuration, but through a more abstracted and potentially easier-to-manage interface. NetworkManager handles the underlying details of configuring the network interfaces.

Conclusion

This guide detailed the process of Network Bridge Configuration on Debian 12 Linux. It covered the definition of a network bridge, its functionality, and the step-by-step instructions to install the bridge-utils package and configure a bridge interface manually. Additionally, it provided two alternative approaches using netplan and nmcli, offering flexibility based on your system’s configuration and preferred management style. Understanding these different methods allows you to choose the best approach for your specific needs when setting up Network Bridge Configuration on Debian 12 Linux.