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Chapter 7. Configuring a network bridge

A network bridge is a link-layer device which forwards traffic between networks based on a table of MAC addresses. The bridge builds the MAC addresses table by listening to network traffic and thereby learning what hosts are connected to each network. For example, you can use a software bridge on a Red Hat Enterprise Linux host to emulate a hardware bridge or in virtualization environments, to integrate virtual machines (VM) to the same network as the host.

A bridge requires a network device in each network the bridge should connect. When you configure a bridge, the bridge is called controller and the devices it uses ports.

You can create bridges on different types of devices, such as:

Physical and virtual Ethernet devices
Network bonds
Network teams
VLAN devices

Due to the IEEE 802.11 standard which specifies the use of 3-address frames in Wi-Fi for the efficient use of airtime, you cannot configure a bridge over Wi-Fi networks operating in Ad-Hoc or Infrastructure modes.

7.1. Configuring a network bridge using nmcli commands

To configure a network bridge on the command line, use the nmcli utility.

Prerequisites

Two or more physical or virtual network devices are installed on the server.
To use Ethernet devices as ports of the bridge, the physical or virtual Ethernet devices must be installed on the server.
To use team, bond, or VLAN devices as ports of the bridge, you can either create these devices while you create the bridge or you can create them in advance as described in:
- Configuring a network team using nmcli commands
- Configuring a network bond using nmcli commands
- Configuring VLAN tagging using nmcli commands

Procedure

Create a bridge interface:
```
# nmcli connection add type bridge con-name 
bridge0
 ifname bridge0
```
This command creates a bridge named bridge0, enter:
Display the network interfaces, and note the names of the interfaces you want to add to the bridge:
```
# nmcli device status
DEVICE  TYPE      STATE         CONNECTION
enp7s0  ethernet  disconnected  --
enp8s0  ethernet  disconnected  --
bond0   bond      connected     bond0
bond1   bond      connected     bond1
...
```
In this example:
- enp7s0 and enp8s0 are not configured. To use these devices as ports, add connection profiles in the next step.
- bond0 and bond1 have existing connection profiles. To use these devices as ports, modify their profiles in the next step.
Assign the interfaces to the bridge.
1. If the interfaces you want to assign to the bridge are not configured, create new connection profiles for them:
```
# nmcli connection add type ethernet slave-type bridge con-name 
bridge0-port1
 ifname enp7s0 master bridge0
# nmcli connection add type ethernet slave-type bridge con-name 
bridge0-port2
 ifname enp8s0 master bridge0
```
  These commands create profiles for enp7s0 and enp8s0, and add them to the bridge0 connection.
2. If you want to assign an existing connection profile to the bridge:
  1. Set the master parameter of these connections to bridge0:
```
# nmcli connection modify 
bond0
 master bridge0
# nmcli connection modify 
bond1
 master bridge0
```
    These commands assign the existing connection profiles named bond0 and bond1 to the bridge0 connection.
  2. Reactivate the connections:
```
# nmcli connection up 
bond0

# nmcli connection up 
bond1
```

Configure the IPv4 settings:

To use this bridge device as a port of other devices, enter:
```
# nmcli connection modify bridge0 ipv4.method disabled
```
To use DHCP, no action is required.

To set a static IPv4 address, network mask, default gateway, and DNS server to the bridge0 connection, enter:

nmcli connection modify bridge0 ipv4.addresses '

192.0.2.1/24

nmcli connection modify bridge0 ipv4.gateway '

192.0.2.254

nmcli connection modify bridge0 ipv4.dns '

192.0.2.253

nmcli connection modify bridge0 ipv4.dns-search '

example.com

nmcli connection modify bridge0 ipv4.method manual

Configure the IPv6 settings:

To use this bridge device as a port of other devices, enter:
```
# nmcli connection modify bridge0 ipv6.method disabled
```
To use DHCP, no action is required.

To set a static IPv6 address, network mask, default gateway, and DNS server to the bridge0 connection, enter:

nmcli connection modify bridge0 ipv6.addresses '

2001:db8:1::1/64

nmcli connection modify bridge0 ipv6.gateway '

2001:db8:1::fffe

nmcli connection modify bridge0 ipv6.dns '

2001:db8:1::fffd

nmcli connection modify bridge0 ipv6.dns-search '

example.com

nmcli connection modify bridge0 ipv6.method manual

Optional: Configure further properties of the bridge. For example, to set the Spanning Tree Protocol (STP) priority of bridge0 to 16384, enter:
```
# nmcli connection modify bridge0 bridge.priority '16384'
```
By default, STP is enabled.
Activate the connection:
```
# nmcli connection up bridge0
```
Verify that the ports are connected, and the CONNECTION column displays the port’s connection name:
```
# nmcli device
DEVICE   TYPE      STATE      CONNECTION
...
enp7s0   ethernet  connected  bridge0-port1
enp8s0   ethernet  connected  bridge0-port2
```
When you activate any port of the connection, NetworkManager also activates the bridge, but not the other ports of it. You can configure that Red Hat Enterprise Linux enables all ports automatically when the bridge is enabled:
1. Enable the connection.autoconnect-slaves parameter of the bridge connection:
```
# nmcli connection modify bridge0 connection.autoconnect-slaves 1
```
2. Reactivate the bridge:
```
# nmcli connection up bridge0
```

Verification steps

Use the ip utility to display the link status of Ethernet devices that are ports of a specific bridge:

ip link show master

bridge0

3: enp7s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master bridge0 state UP mode DEFAULT group default qlen 1000 link/ether 52:54:00:62:61:0e brd ff:ff:ff:ff:ff:ff 4: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master bridge0 state UP mode DEFAULT group default qlen 1000 link/ether 52:54:00:9e:f1:ce brd ff:ff:ff:ff:ff:ff

Use the bridge utility to display the status of Ethernet devices that are ports of any bridge device:

bridge link show

3: enp7s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master bridge0 state forwarding priority 32 cost 100 4: enp8s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master bridge0 state listening priority 32 cost 100 5: enp9s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master bridge1 state forwarding priority 32 cost 100 6: enp11s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master bridge1 state blocking priority 32 cost 100 ...

To display the status for a specific Ethernet device, use the bridge link show dev ethernet_device_name command.

Additional resources

Configuring NetworkManager to avoid using a specific profile to provide a default gateway
nm-settings(5) man page
bridge(8) man page
NetworkManager duplicates a connection after restart of NetworkManager service
How to configure bridge with vlan information?

7.2. Configuring a network bridge using the RHEL web console

Use the RHEL web console to configure a network bridge if you prefer to manage network settings using a web browser-based interface.

Prerequisites

Two or more physical or virtual network devices are installed on the server.
To use Ethernet devices as ports of the bridge, the physical or virtual Ethernet devices must be installed on the server.
To use team, bond, or VLAN devices as ports of the bridge, you can either create these devices while you create the bridge or you can create them in advance as described in:
- Configuring a network team using the RHEL web console
- Configuring a network bond using the RHEL web console
- Configuring VLAN tagging using the RHEL web console

Procedure

Select the Networking tab in the navigation on the left side of the screen.
Click

Add bridge

in the Interfaces section.
Enter the name of the bridge device you want to create.
Select the interfaces that should be ports of the bridge.
Optional: Enable the Spanning tree protocol (STP) feature to avoid bridge loops and broadcast radiation.
Click

Apply

.
By default, the bridge uses a dynamic IP address. If you want to set a static IP address:
1. Click the name of the bridge in the Interfaces section.
2. Click Edit next to the protocol you want to configure.
3. Select Manual next to Addresses, and enter the IP address, prefix, and default gateway.
4. In the DNS section, click the
  
  +
  
  button, and enter the IP address of the DNS server. Repeat this step to set multiple DNS servers.
5. In the DNS search domains section, click the
  
  +
  
  button, and enter the search domain.
6. If the interface requires static routes, configure them in the Routes section.
7. Click
  
  Apply

Verification

Select the Networking tab in the navigation on the left side of the screen, and check if there is incoming and outgoing traffic on the interface:

7.3. Configuring a network bridge using nmtui

The nmtui application provides a text-based user interface for NetworkManager. You can use nmtui to configure a network bridge on a host without a graphical interface.

Note

In nmtui:

Navigate by using the cursor keys.
Press a button by selecting it and hitting

Enter

.
Select and deselect checkboxes by using

Space

.

Prerequisites

Two or more physical or virtual network devices are installed on the server.
To use Ethernet devices as ports of the bridge, the physical or virtual Ethernet devices must be installed on the server.

Procedure

If you do not know the network device names on which you want configure a network bridge, display the available devices:

nmcli device status

DEVICE TYPE STATE CONNECTION

enp7s0

ethernet unavailable --

enp8s0

ethernet unavailable -- ...

Start nmtui:
```
# nmtui
```
Select Edit a connection, and press

Enter

.
Press the Add button.
Select Bridge from the list of network types, and press

Enter

.
Optional: Enter a name for the NetworkManager profile to be created.
Enter the bridge device name to be created into the Device field.
Add ports to the bridge to be created:
1. Press the Add button next to the Slaves list.
2. Select the type of the interface you want to add as port to the bridge, for example, Ethernet.
3. Optional: Enter a name for the NetworkManager profile to be created for this bridge port.
4. Enter the port’s device name into the Device field.
5. Press the OK button to return to the window with the bridge settings.
  
  Figure 7.1. Adding an Ethernet device as port to a bridge
6. Repeat these steps to add more ports to the bridge.
Depending on your environment, configure the IP address settings in the IPv4 configuration and IPv6 configuration areas accordingly. For this, press the Automatic button, and select:
- Disabled, if the bridge does not require an IP address.
- Automatic, if a DHCP server dynamically assigns an IP address to the bridge.
- Manual, if the network requires static IP address settings. In this case, you must fill further fields:
  1. Press the Show button next to the protocol you want to configure to display additional fields.
  2. Press the Add button next to Addresses, and enter the IP address and the subnet mask in Classless Inter-Domain Routing (CIDR) format.
    
    If you do not specify a subnet mask, NetworkManager sets a /32 subnet mask for IPv4 addresses and /64 for IPv6 addresses.
  3. Enter the address of the default gateway.
  4. Press the Add button next to DNS servers, and enter the DNS server address.
  5. Press the Add button next to Search domains, and enter the DNS search domain.
Figure 7.2. Example of a bridge connection without IP address settings
Press the OK button to create and automatically activate the new connection.
Press the Back button to return to the main menu.
Select Quit, and press

Enter

to close the nmtui application.

Verification

Use the ip utility to display the link status of Ethernet devices that are ports of a specific bridge:

ip link show master

bridge0

Use the bridge utility to display the status of Ethernet devices that are ports of any bridge device:

bridge link show

To display the status for a specific Ethernet device, use the bridge link show dev ethernet_device_name command.

7.4. Configuring a network bridge using nm-connection-editor

If you use Red Hat Enterprise Linux with a graphical interface, you can configure network bridges using the nm-connection-editor application.

Note that nm-connection-editor can add only new ports to a bridge. To use an existing connection profile as a port, create the bridge using the nmcli utility as described in Configuring a network bridge using nmcli commands.

Prerequisites

Two or more physical or virtual network devices are installed on the server.
To use Ethernet devices as ports of the bridge, the physical or virtual Ethernet devices must be installed on the server.
To use team, bond, or VLAN devices as ports of the bridge, ensure that these devices are not already configured.

Procedure

Open a terminal, and enter nm-connection-editor:
```
$ nm-connection-editor
```
Click the

+

button to add a new connection.
Select the Bridge connection type, and click

Create

.
In the Bridge tab:
1. Optional: Set the name of the bridge interface in the Interface name field.
2. Click the Add button to create a new connection profile for a network interface and adding the profile as a port to the bridge.
  1. Select the connection type of the interface. For example, select Ethernet for a wired connection.
  2. Optionally, set a connection name for the port device.
  3. If you create a connection profile for an Ethernet device, open the Ethernet tab, and select in the Device field the network interface you want to add as a port to the bridge. If you selected a different device type, configure it accordingly.
  4. Click
    
    Save
    
    .
3. Repeat the previous step for each interface you want to add to the bridge.
Optional: Configure further bridge settings, such as Spanning Tree Protocol (STP) options.
Configure the IP settings of the bridge. Skip this step if you want to use this bridge as a port of other devices.
1. In the IPv4 Settings tab, configure the IPv4 settings. For example, set a static IPv4 address, network mask, default gateway, DNS server, and DNS search domain:
2. In the IPv6 Settings tab, configure the IPv6 settings. For example, set a static IPv6 address, network mask, default gateway, DNS server, and DNS search domain:
Save the bridge connection.
Close nm-connection-editor.

Verification steps

Use the ip utility to display the link status of Ethernet devices that are ports of a specific bridge.

ip link show master

bridge0

Use the bridge utility to display the status of Ethernet devices that are ports in any bridge device:

bridge link show

To display the status for a specific Ethernet device, use the bridge link show dev ethernet_device_name command.

Additional resources

Configuring a network bond using nm-connection-editor
Configuring a network team using nm-connection-editor
Configuring VLAN tagging using nm-connection-editor
Configuring NetworkManager to avoid using a specific profile to provide a default gateway
How to configure bridge with vlan information?

7.5. Configuring a network bridge using nmstatectl

To configure a network bridge using the Nmstate API, use the nmstatectl utility.

For example, the procedure below creates a bridge in NetworkManager with the following settings:

Network interfaces in the bridge: enp1s0 and enp7s0
Spanning Tree Protocol (STP): Enabled
Static IPv4 address: 192.0.2.1 with the /24 subnet mask
Static IPv6 address: 2001:db8:1::1 with the /64 subnet mask
IPv4 default gateway: 192.0.2.254
IPv6 default gateway: 2001:db8:1::fffe
IPv4 DNS server: 192.0.2.200
IPv6 DNS server: 2001:db8:1::ffbb
DNS search domain: example.com

Prerequisites

Two or more physical or virtual network devices are installed on the server.
To use Ethernet devices as ports in the bridge, the physical or virtual Ethernet devices must be installed on the server.
To use team, bond, or VLAN devices as ports in the bridge, set the interface name in the port list, and define the corresponding interfaces.
The nmstate package is installed.

Procedure

Create a YAML file, for example ~/create-bridge.yml, with the following contents:

---
interfaces:
- name: bridge0
  type: linux-bridge
  state: up
  ipv4:
    enabled: true
    address:
    - ip: 192.0.2.1
      prefix-length: 24
    dhcp: false
  ipv6:
    enabled: true
    address:
    - ip: 2001:db8:1::1
      prefix-length: 64
    autoconf: false
    dhcp: false
  bridge:
    options:
      stp:
        enabled: true
    port:
      - name: enp1s0
      - name: enp7s0
- name: enp1s0
  type: ethernet
  state: up
- name: enp7s0
  type: ethernet
  state: up

routes:
  config:
  - destination: 0.0.0.0/0
    next-hop-address: 192.0.2.254
    next-hop-interface: bridge0
  - destination: ::/0
    next-hop-address: 2001:db8:1::fffe
    next-hop-interface: bridge0
dns-resolver:
  config:
    search:
    - example.com
    server:
    - 192.0.2.200
    - 2001:db8:1::ffbb

Apply the settings to the system:
```
# nmstatectl apply ~/create-bridge.yml
```

Verification steps

Display the status of the devices and connections:

nmcli device status

DEVICE TYPE STATE CONNECTION

bridge0

bridge

connected

bridge0

Display all settings of the connection profile:

nmcli connection show

bridge0

connection.id:

bridge0

connection.uuid:

e2cc9206-75a2-4622-89cf-1252926060a9

connection.stable-id: -- connection.type: bridge connection.interface-name:

bridge0

...

Display the connection settings in YAML format:
```
# nmstatectl show 
bridge0
```

Additional resources

nmstatectl(8) man page
/usr/share/doc/nmstate/examples/ directory
How to configure bridge with vlan information?

7.6. Configuring a network bridge using RHEL System Roles

You can use the network RHEL System Role to configure a Linux bridge. For example, use it to configure a network bridge that uses two Ethernet devices, and sets IPv4 and IPv6 addresses, default gateways, and DNS configuration.

Note

Set the IP configuration on the bridge and not on the ports of the Linux bridge.

Perform this procedure on the Ansible control node.

Prerequisites

You have prepared the control node and the managed nodes
You are logged in to the control node as a user who can run playbooks on the managed nodes.
The account you use to connect to the managed nodes has sudo permissions on them.
The hosts or host groups on which you want to run this playbook are listed in the Ansible inventory file.

Two or more physical or virtual network devices are installed on the server.

Procedure

Create a playbook file, for example ~/bridge-ethernet.yml, with the following content:

--- - name: Configure the network hosts:

managed-node-01.example.com

tasks: - name: Configure a network bridge that uses two Ethernet ports include_role: name: rhel-system-roles.network vars: network_connections: # Define the bridge profile - name: bridge0 type: bridge interface_name: bridge0 ip: address: - "192.0.2.1/24" - "2001:db8:1::1/64" gateway4: 192.0.2.254 gateway6: 2001:db8:1::fffe dns: - 192.0.2.200 - 2001:db8:1::ffbb dns_search: - example.com state: up # Add an Ethernet profile to the bridge - name: bridge0-port1 interface_name: enp7s0 type: ethernet controller: bridge0 port_type: bridge state: up # Add a second Ethernet profile to the bridge - name: bridge0-port2 interface_name: enp8s0 type: ethernet controller: bridge0 port_type: bridge state: up

Run the playbook:

ansible-playbook

~/bridge-ethernet.yml

Additional resources