Chapter 6. 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.

6.1. Configuring a network bridge by using nmcli

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

Prerequisites

Procedure

  1. Create a bridge interface: 

    # nmcli connection add type bridge con-name bridge0 ifname bridge0

    This command creates a bridge named bridge0, enter:

  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 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

  4. 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' ipv4.gateway '192.0.2.254' ipv4.dns '192.0.2.253' ipv4.dns-search 'example.com' ipv4.method manual

  5. 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' ipv6.gateway '2001:db8:1::fffe' ipv6.dns '2001:db8:1::fffd' ipv6.dns-search 'example.com' ipv6.method manual

  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-slaves parameter of the bridge connection: 

      # nmcli connection modify bridge0 connection.autoconnect-slaves 1

    2. Reactivate the bridge: 

      # nmcli connection up bridge0

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
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

6.2. Configuring a network bridge by 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

Procedure

  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.

    bridge settings
  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.

      bond team bridge vlan.ipv4
    7. Click Apply

Verification

  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:

    bridge verify

6.3. Configuring a network bridge by 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

  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 the Add button.
  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 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 6.1. Adding an Ethernet device as port to a bridge

      nmtui bridge add port
    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 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 6.2. Example of a bridge connection without IP address settings

    nmtui bridge no IP
  10. Press the OK button to create and automatically activate the new connection.
  11. Press the Back button to return to the main menu.
  12. Select Quit, and press Enter to close the nmtui application.

Verification

  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.

6.4. Configuring a network bridge by 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 by using nmcli.

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

  1. Open a terminal, and enter nm-connection-editor: 

    $ nm-connection-editor
  2. Click the + button to add a new connection.
  3. Select the Bridge connection type, and click Create.

  4. On 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.

      add nic to bridge in nm connection editor

  5. Optional: Configure further bridge settings, such as Spanning Tree Protocol (STP) options.

  6. Configure the IP address settings on both the IPv4 Settings and IPv6 Settings tabs:

    • To use this bridge device as a port of other devices, set the Method field to Disabled.
    • To use DHCP, leave the Method field at its default, Automatic (DHCP).

    • To use static IP settings, set the Method field to Manual and fill the fields accordingly:

      bridge IP settings nm connection editor

  7. Click Save.
  8. Close nm-connection-editor.

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
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 in 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

6.5. Configuring a network bridge by using nmstatectl

Use the nmstatectl utility to configure a network bridge through the Nmstate API. The Nmstate API ensures that, after setting the configuration, the result matches the configuration file. If anything fails, nmstatectl automatically rolls back the changes to avoid leaving the system in an incorrect state.

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.

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

  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

Verification

  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

Additional resources

6.6. Configuring a network bridge by using the network RHEL System Role

You can remotely configure a network bridge by using the network RHEL System Role.

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 managed nodes or groups of managed nodes 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

  1. 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

    These settings define a network bridge with the following settings:

    • A static IPv4 address - 192.0.2.1 with a /24 subnet mask
    • A static IPv6 address - 2001:db8:1::1 with a /64 subnet mask
    • An IPv4 default gateway - 192.0.2.254
    • An IPv6 default gateway - 2001:db8:1::fffe
    • An IPv4 DNS server - 192.0.2.200
    • An IPv6 DNS server - 2001:db8:1::ffbb
    • A DNS search domain - example.com

    • Ports of the bridge - enp7s0 and enp8s0

      Note

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

  2. Validate the playbook syntax: 

    # ansible-playbook ~/bridge-ethernet.yml --syntax-check

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

  3. Run the playbook: 

    # ansible-playbook ~/bridge-ethernet.yml

Additional resources

  • /usr/share/ansible/roles/rhel-system-roles.network/README.md file