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⁠Chapter 6. Configure Network Bridging

6.1. Using NetworkManager
6.1.1. Establishing a Bridge Connection
6.2. Using the Command Line Interface (CLI)
6.2.1. Check if Bridging Kernel Module is Installed
6.2.2. Create a Network Bridge
6.3. Using the NetworkManager Command Line Tool, nmcli
6.4. Additional Resources
6.4.1. Installed Documentation
A network bridge is a link-layer device which forwards traffic between networks based on MAC addresses. It makes forwarding decisions based on a table of MAC addresses which it builds by listening to network traffic and thereby learning what hosts are connected to each network. A software bridge can be used within a Linux host in order to emulate a hardware bridge, for example in virtualization applications for sharing a NIC with one or more virtual NICs.
Note that a bridge cannot be established over Wi-Fi networks operating in Ad-Hoc or Infrastructure modes. This is due to the IEEE 802.11 standard that specifies the use of 3-address frames in Wi-Fi for the efficient use of airtime. A system configured to be an access point (AP) running the hostapd can support the necessary 4-address frames.

⁠6.1. Using NetworkManager

When starting a bridge interface, NetworkManager waits for at least one port to enter the “forwarding” state before beginning any network-dependent IP configuration such as DHCP or IPv6 autoconfiguration. Static IP addressing is allowed to proceed before any slaves or ports are connected or begin forwarding packets.

⁠6.1.1. Establishing a Bridge Connection

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Procedure 6.1. Adding a New Bridge Connection

  1. You can configure a new Bridge connection by opening the Network window and selecting the plus symbol below the menu.
  2. To use the graphical Network settings tool, press the Super key to enter the Activities Overview, type control network and then press Enter. The Network settings tool appears.
  3. Select the plus symbol below the menu. The Add Network Connection window appears.
  4. Select the Bridge menu entry. The Editing Bridge connection 1 window appears.
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Procedure 6.2. Editing an Existing Bridge Connection

You can configure an existing bridge connection by opening the Network window and selecting the name of the connection from the list. Then click the Edit button.
  1. Press the Super key to enter the Activities Overview, type control network and then press Enter. The Network settings tool appears.
  2. Select the Bridge connection you wish to edit from the left hand menu.
  3. Click the Options button.

⁠Configuring the Connection Name, Auto-Connect Behavior, and Availability Settings

Five settings in the Editing dialog are common to all connection types, see the General tab:
  • Connection name — Enter a descriptive name for your network connection. This name will be used to list this connection in the menu of the Network window.
  • Automatically connect to this network when it is available — Select this box if you want NetworkManager to auto-connect to this connection when it is available. See Section 2.2.3, “Connecting to a Network Automatically” for more information.
  • All users may connect to this network — Select this box to create a connection available to all users on the system. Changing this setting may require root privileges. See Section 2.2.4, “System-wide and Private Connection Profiles” for details. To prevent unexpected behavior during installation, ensure that this check box remains selected for any network interface that you configure.
  • Automatically connect to VPN when using this connection — Select this box if you want NetworkManager to auto-connect to a VPN connection when it is available. Select the VPN from the dropdown menu.
  • Firewall Zone — Select the Firewall Zone from the dropdown menu.

⁠Configuring the Bridge Tab

Interface name
The name of the interface to the bridge.
Bridged connections
One or more slave interfaces.
Aging time
The time, in seconds, a MAC address is kept in the MAC address forwarding database.
Enable STP (Spanning Tree Protocol)
If required, select the check box to enable STP.
Priority
The bridge priority; the bridge with the lowest priority will be elected as the root bridge.
Forward delay
The time, in seconds, spent in both the Listening and Learning states before entering the Forwarding state.
Hello time
The time interval, in seconds, between sending configuration information in bridge protocol data units (BPDU).
Max age
The maximum time, in seconds, to store the configuration information from BPDUs. This value should be twice the Hello Time plus 1 but less than twice the Forwarding delay minus 1.
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⁠Editing Bridge Connection 1

Figure 6.1. Editing Bridge Connection 1

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Procedure 6.3. Adding a Slave Interface to a Bridge

  1. To add a port to a bridge, select the Bridge tab in the Editing Bridge connection 1 window. If necessary, open this window by following the procedure in Procedure 6.2, “Editing an Existing Bridge Connection”.
  2. Click Add. The Choose a Connection Type menu appears.
  3. Select the type of connection to be created from the list. Click Create. A window appropriate to the connection type selected appears.
  4. Select the Bridge Port tab. Configure Priority and Path cost as required. Note the STP priority for a bridge port is limited by the Linux kernel. Although the standard allows a range of 0 to 255, Linux only allows 0 to 63. The default is 32 in this case.
  5. If required, select the Hairpin mode check box to enable forwarding of frames for external processing. Also known as virtual Ethernet port aggregator (VEPA) mode.

⁠Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your new bridge connection, click the Save button to save your customized configuration. To make NetworkManager apply the changes, power cycle the interface. See Section 2.2.1, “Connecting to a Network Using a GUI” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network window and clicking Configure to return to the Editing dialog.
Then, to configure: