Configure a network bridge

A network bridge is a link-layer device that forwards traffic between networks by using a MAC address table. For example, you can use a software bridge to connect virtual machines 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
  • Virtual Local Area Network (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.

Red Hat Enterprise Linux provides administrators different options to configure bridge devices. For example:

  • Use nmcli to configure VLAN tagging using the command line.
  • Use the RHEL web console to configure VLAN tagging using a web browser.
  • Use nmtui to configure VLAN tagging in a text-based user interface.
  • Use nmstatectl to configure connections through the Nmstate API.
  • Use RHEL system roles to automate the VLAN configuration on one or multiple hosts.

Configure a network bridge by using nmcli
Copy link

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

Before you begin
Copy link

  • 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 bond or Virtual Local Area Network (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:

Procedure
Copy link

  1. Create a bridge interface: 
    # nmcli connection add type bridge con-name bridge0 ifname bridge0

    This command creates a bridge named bridge0.

  2. 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.
  3. 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 port-type bridge con-name bridge0-port1 ifname enp7s0 controller bridge0
# nmcli connection add type ethernet port-type bridge con-name bridge0-port2 ifname enp8s0 controller 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
  4. Configure the IPv4 settings:
    • 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' ipv4.gateway '192.0.2.254' ipv4.dns '192.0.2.253' ipv4.dns-search 'example.com' ipv4.method manual
    • To use DHCP, no action is required.
    • If you plan to use this bridge device as a port of other devices, no action is required.
  5. Configure the IPv6 settings:
    • 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' ipv6.gateway '2001:db8:1::fffe' ipv6.dns '2001:db8:1::fffd' ipv6.dns-search 'example.com' ipv6.method manual
    • To use stateless address autoconfiguration (SLAAC), no action is required.
    • If you plan to use this bridge device as a port of other devices, no action is required.
  6. 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.

  7. Activate the connection: 
    # nmcli connection up bridge0
  8. 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-ports parameter of the bridge connection: 
      # nmcli connection modify bridge0 connection.autoconnect-ports 1
    2. Reactivate the bridge: 
      # nmcli connection up bridge0

Results
Copy link

  • 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.

Configure a network bridge by using the RHEL web console
Copy link

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

Before you begin
Copy link

Procedure
Copy link

  1. Select the Networking tab in the navigation on the left side of the screen.
  2. Click Add bridge in the Interfaces section.
  3. Enter the name of the bridge device you want to create.
  4. Select the interfaces that should be ports of the bridge.
  5. Optional: Enable the Spanning tree protocol (STP) feature to avoid bridge loops and broadcast radiation.
  6. Click Apply.
  7. 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

Results
Copy link

  1. 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.

Configure a network bridge by using nmtui
Copy link

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.

Before you begin
Copy link

  • 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.

About this task
Copy link

Note

In nmtui:

  • Navigate by using the cursor keys.
  • Press a button by selecting it and hitting Enter.
  • Select and clear checkboxes by using Space.
  • To return to the previous screen, use ESC.

Procedure
Copy link

  1. 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             --
...
  2. Start nmtui: 
    # nmtui
  3. Select Edit a connection, and press Enter.
  4. Press Add.
  5. Select Bridge from the list of network types, and press Enter.
  6. Optional: Enter a name for the NetworkManager profile to be created.

    On hosts with multiple profiles, a meaningful name makes it easier to identify the purpose of a profile.

  7. Enter the bridge device name to be created into the Device field.
  8. Add ports to the bridge to be created:
    1. Press Add next to the Ports list.
    2. Select the type of the interface you want to add as a 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 OK to return to the window with the bridge settings.
    6. Repeat these steps to add more ports to the bridge.
  9. Depending on your environment, configure the IP address settings in the IPv4 configuration and IPv6 configuration areas accordingly. For this, press the button next to these areas, and select:
    • Disabled, if the bridge does not require an IP address.
    • Automatic, if a DHCP server or stateless address autoconfiguration (SLAAC) 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 Show next to the protocol you want to configure to display additional fields.
      2. Press Add 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 Add next to DNS servers, and enter the DNS server address.
      5. Press Add next to Search domains, and enter the DNS search domain.
  10. Press OK to create and automatically activate the new connection.
  11. Press Back to return to the main menu.
  12. Select Quit, and press Enter to close the nmtui application.

Results
Copy link

  1. 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
  2. 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
...

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

Configure a network bridge by using nmstatectl
Copy link

You can use the declarative Nmstate API to configure a network bridge. Nmstate ensures that the result matches the configuration file or rolls back the changes.

Before you begin
Copy link

  • 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 bond or Virtual Local Area Network (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.

About this task
Copy link

Depending on your environment, adjust the YAML file accordingly. For example, to use different devices than Ethernet adapters in the bridge, adapt the base-iface attribute and type attributes of the ports you use in the bridge.

Procedure
Copy link

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

    These settings define a network bridge 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
  2. Apply the settings to the system: 
    # nmstatectl apply ~/create-bridge.yml

Results
Copy link

  1. Display the status of the devices and connections: 
    # nmcli device status
     
    DEVICE      TYPE      STATE      CONNECTION
bridge0     bridge    connected  bridge0
  2. 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
...
  3. Display the connection settings in YAML format: 
    # nmstatectl show bridge0

Configure a network bridge by using the network RHEL system role
Copy link

You can use the network RHEL system role to configure a bridge and, if a connection profile for the bridge’s parent device does not exist, the role can create it as well.

Before you begin
Copy link

  • 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 for these nodes.
  • Two or more physical or virtual network devices are installed on the server.

About this task
Copy link

You can connect multiple networks on layer 2 of the Open Systems Interconnection (OSI) model by creating a network bridge. To configure a bridge, create a connection profile in NetworkManager. By using Ansible and the network RHEL system role, you can automate this process and remotely configure connection profiles on the hosts defined in a playbook.

Note

If you want to assign IP addresses, gateways, and DNS settings to a bridge, configure them on the bridge and not on its ports.

Procedure
Copy link

  1. Create a playbook file, for example, ~/playbook.yml, with the following content: 
    ---
- name: Configure the network
  hosts: managed-node-01.example.com
  tasks:
    - name: Bridge connection profile with two Ethernet ports
      ansible.builtin.include_role:
        name: redhat.rhel_system_roles.network
      vars:
        network_connections:
          # Bridge profile
          - name: bridge0
            type: bridge
            interface_name: bridge0
            ip:
              dhcp4: yes
              auto6: yes
            state: up

          # Port profile for the 1st Ethernet device
          - name: bridge0-port1
            interface_name: enp7s0
            type: ethernet
            controller: bridge0
            port_type: bridge
            state: up

          # Port profile for the 2nd Ethernet device
          - name: bridge0-port2
            interface_name: enp8s0
            type: ethernet
            controller: bridge0
            port_type: bridge
            state: up

    The settings specified in the example playbook include the following:

    type: <profile_type>
    Sets the type of the profile to create. The example playbook creates three connection profiles: One for the bridge and two for the Ethernet devices.
    dhcp4: yes
    Enables automatic IPv4 address assignment from DHCP, PPP, or similar services.
    auto6: yes
    Enables IPv6 auto-configuration. By default, NetworkManager uses Router Advertisements. If the router announces the managed flag, NetworkManager requests an IPv6 address and prefix from a DHCPv6 server.

    For details about all variables used in the playbook, see the /usr/share/ansible/roles/rhel-system-roles.network/README.md file on the control node.

  2. Validate the playbook syntax: 
    $ ansible-playbook --syntax-check ~/playbook.yml

    Note that this command only validates the syntax and does not protect against a wrong but valid configuration.

  3. Run the playbook: 
    $ ansible-playbook ~/playbook.yml

Results
Copy link

  1. Display the link status of Ethernet devices that are ports of a specific bridge: 
    # ansible managed-node-01.example.com -m command -a 'ip link show master bridge0'
     
    managed-node-01.example.com | CHANGED | rc=0 >>
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
  2. Display the status of Ethernet devices that are ports of any bridge device: 
    # ansible managed-node-01.example.com -m command -a 'bridge link show'
     
    managed-node-01.example.com | CHANGED | rc=0 >>
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