The
brconfig utility is used to configure network bridge parameters and retrieve network bridge parameters and status from the kernel. The bridging function is implemented by the
bridge(4) driver.
A network bridge creates a logical link between two or more IEEE 802 networks that use the same (or “similar enough”) framing format. For example, it is possible to bridge Ethernet and 802.11 networks together, but it is not possible to bridge Ethernet and Token Ring together.
Bridge interfaces are created using the
ifconfig(8) command's “create” sub-command. All other bridge configuration is performed using
brconfig.
The options are as follows:
-a
Display the status of all bridge devices present on the system. This flag is mutually exclusive with all other sub-commands.
All other operations require that a bridge be specified. If a bridge is specified with no sub-commands, the status of that bridge is displayed. The following sub-commands are available:
up
Start forwarding packets on the bridge.
down
Stop forwarding packets on the bridge.
add interface
Add the interface named by interface as a member of the bridge. The interface is put into promiscuous mode so that it can receive every packet sent on the network.
delete interface
Remove the interface named by interface from the bridge. Promiscuous mode is disabled on the interface when it is removed from the bridge.
maxaddr size
Set the size of the bridge address cache to size. The default is 100 entries.
timeout seconds
Set the timeout of address cache entries to seconds seconds. If seconds is zero, then address cache entries will not be expired. The default is 1200 seconds.
deladdr address
Delete address from the address cache.
flush
Delete all dynamically-learned addresses from the address cache.
flushall
Delete all addresses, including static addresses, from the address cache.
discover interface
Mark an interface as a “discovering” interface. When the bridge has no address cache entry (either dynamic or static) for the destination address of a packet, the bridge will forward the packet to all member interfaces marked as “discovering”. This is the default for all interfaces added to a bridge.
-discover interface
Clear the “discovering” attribute on a member interface. For packets without the “discovering” attribute, the only packets forwarded on the interface are broadcast or multicast packets and packets for which the destination address is known to be on the interface's segment.
ipf
Enable packet filtering with
pfil(9) on the bridge. The current implementation passes all ARP and RARP packets through the bridge while filtering IP and IPv6 packets through the configured packet filter, such as
ipf(4) or
pf(4). Other packet types are blocked.
learn interface
Mark an interface as a “learning” interface. When a packet arrives on such an interface, the source address of the packet is entered into the address cache as being a destination address on the interface's segment. This is the default for all interfaces added to a bridge.
-learn interface
Clear the “learning” attribute on a member interface.
stp interface
Enable Spanning Tree protocol on
interface. The
bridge(4) driver has support for the IEEE 802.1D Spanning Tree protocol (STP). Spanning Tree is used to detect and remove loops in a network topology.
-stp interface
Disable Spanning Tree protocol on interface. This is the default for all interfaces added to a bridge.
maxage seconds
Set the time that a Spanning Tree protocol configuration is valid. The default is 20 seconds. The minimum is 1 second and the maximum is 255 seconds.
fwddelay seconds
Set the time that must pass before an interface begins forwarding packets when Spanning Tree is enabled. The default is 15 seconds. The minimum is 1 second and the maximum is 255 seconds.
hellotime seconds
Set the time between broadcasting of Spanning Tree protocol configuration messages. The default is 2 seconds. The minimum is 1 second and the maximum is 255 seconds.
priority value
Set the bridge priority for Spanning Tree. The default is 32768. Allowed numerical values range from 0 (highest priority) to 65535 (lowest priority).
ifpriority interface value
Set the Spanning Tree priority of interface to value. The default is 128. The minimum is 0 and the maximum is 255.
ifpathcost interface value
Set the Spanning Tree path cost of interface to value. The default is 55. The minimum is 0 and the maximum is 65535.