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
- 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.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' ipv4.gateway '192.0.2.254' ipv4.dns '192.0.2.253' ipv4.dns-search 'example.com' 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' ipv6.gateway '2001:db8:1::fffe' ipv6.dns '2001:db8:1::fffd' ipv6.dns-search 'example.com' 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 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
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
- 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
-
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:
-
Click the name of the bridge in the
Interfaces
section. -
Click
Edit
next to the protocol you want to configure. -
Select
Manual
next toAddresses
, and enter the IP address, prefix, and default gateway. -
In the
DNS
section, click the + button, and enter the IP address of the DNS server. Repeat this step to set multiple DNS servers. -
In the
DNS search domains
section, click the + button, and enter the search domain. If the interface requires static routes, configure them in the
Routes
section.- Click Apply
-
Click the name of the bridge in the
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:
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.
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.
On hosts with multiple profiles, a meaningful name makes it easier to identify the purpose of a profile.
-
Enter the bridge device name to be created into the
Device
field. Add ports to the bridge to be created:
-
Press the
Add
button next to theSlaves
list. -
Select the type of the interface you want to add as port to the bridge, for example,
Ethernet
. - Optional: Enter a name for the NetworkManager profile to be created for this bridge port.
-
Enter the port’s device name into the
Device
field. 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
- Repeat these steps to add more ports to the bridge.
-
Press the
Depending on your environment, configure the IP address settings in the
IPv4 configuration
andIPv6 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:-
Press the
Show
button next to the protocol you want to configure to display additional fields. Press the
Add
button next toAddresses
, 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.- Enter the address of the default gateway.
-
Press the
Add
button next toDNS servers
, and enter the DNS server address. -
Press the
Add
button next toSearch domains
, and enter the DNS search domain.
-
Press the
Figure 6.2. 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 thenmtui
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 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 ...
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
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.
On 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 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.
- Click Save.
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 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:
- Click Save.
-
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
- Configuring a network bond by using nm-connection-editor
- Configuring a network team by using nm-connection-editor
- Configuring VLAN tagging by using nm-connection-editor
- Configuring NetworkManager to avoid using a specific profile to provide a default gateway
- How to configure a bridge with VLAN information?
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
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
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
-
Network interfaces in the bridge:
Apply the settings to the system:
# nmstatectl apply ~/create-bridge.yml
Verification
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 a bridge with VLAN information?
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
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
andenp8s0
NoteSet the IP configuration on the bridge and not on the ports of the Linux bridge.
-
A static IPv4 address -
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.
Run the playbook:
# ansible-playbook ~/bridge-ethernet.yml
Additional resources
-
/usr/share/ansible/roles/rhel-system-roles.network/README.md
file