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Chapter 10. 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.
10.1. Configuring a network bridge using nmcli commands
This section explains how to configure a network bridge using 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:
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
andenp8s0
are not configured. To use these devices as ports, add connection profiles in the next step. -
bond0
andbond1
have existing connection profiles. To use these devices as ports, modify their profiles in the next step.
-
Assign the interfaces to the bridge.
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
andenp8s0
, and add them to thebridge0
connection.If you want to assign an existing connection profile to the bridge, set the
master
parameter of these connections tobridge0
:# nmcli connection modify bond0 master bridge0 # nmcli connection modify bond1 master bridge0
These commands assign the existing connection profiles named
bond0
andbond1
to thebridge0
connection.
Configure the IP settings of the bridge. Skip this step if you want to use this bridge as a ports of other devices.
Configure the IPv4 settings. For example, to set a static IPv4 address, network mask, default gateway, DNS server, and DNS search domain of 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. For example, to set a static IPv6 address, network mask, default gateway, DNS server, and DNS search domain of 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
to16384
, 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 when the bridge is enabled:
Enable the
connection.autoconnect-slaves
parameter of the bridge connection:# nmcli connection modify bridge0 connection.autoconnect-slaves 1
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
- Testing basic network settings
- Configuring NetworkManager to avoid using a specific profile to provide a default gateway
-
nmcli-examples(7)
man page -
The
bridge settings
section in thenm-settings(5)
man page -
The
bridge-port settings
section in thenm-settings(5)
man page -
bridge(8)
man page - NetworkManager duplicates a connection after restart of NetworkManager service
- How to configure bridge with vlan information?
10.2. Configuring a network bridge using nm-connection-editor
This section explains how to configure a network bridge 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:-
Optional: Set the name of the bridge interface in the
Interface name
field. Click the Add button to create a new connection profile for a network interface and adding the profile as a port to the bridge.
-
Select the connection type of the interface. For example, select
Ethernet
for a wired connection. - Optionally, set a connection name for the port device.
-
If you create a connection profile for an Ethernet device, open the
Ethernet
tab, and select in theDevice
field the network interface you want to add as a port to the bridge. If you selected a different device type, configure it accordingly. - Click Save.
-
Select the connection type of the interface. For example, select
Repeat the previous step for each interface you want to add to the bridge.
-
Optional: Set the name of the bridge interface in the
- 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.
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: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 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
- Configuring a network bond using nm-connection-editor
- Configuring a network team using nm-connection-editor
- Configuring VLAN tagging using nm-connection-editor
- Testing basic network settings
- Configuring NetworkManager to avoid using a specific profile to provide a default gateway
- How to configure bridge with vlan information?
10.3. Configuring a network bridge using nmstatectl
This section describes how to use the nmstatectl
utility to configure a Linux network bridge bridge0
with following settings:
-
Network interfaces in the bridge:
enp1s0
andenp7s0
- 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/
- How to configure bridge with vlan information?