NAME

brconfig — configure network bridge parameters

SYNOPSIS

brconfig

-a

brconfig

bridge

brconfig

bridge command [args ...]

DESCRIPTION

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.

addr

Display the addresses that have been learned by 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.

static interface address

Add a static entry into the address cache pointing to interface. Static entries are never aged out of the cache or replaced, even if the address is seen on a different 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.

EXAMPLES

The following, when placed in the file /etc/ifconfig.bridge0, will cause a bridge called ‘bridge0’ to be created, add the interfaces ‘ray0’ and ‘fxp0’ to the bridge, and then enable packet forwarding. Such a configuration could be used to implement a simple 802.11-to-Ethernet bridge (assuming the 802.11 interface is in ad-hoc mode).

create 
!brconfig $int add ray0 add fxp0 up

Consider a system with two 4-port Ethernet boards. The following placed in the file /etc/ifconfig.bridge0 will cause a bridge consisting of all 8 ports with Spanning Tree enabled to be created:

create 
!brconfig $int \ 
    add tlp0 stp tlp0 \ 
    add tlp1 stp tlp1 \ 
    add tlp2 stp tlp2 \ 
    add tlp3 stp tlp3 \ 
    add tlp4 stp tlp4 \ 
    add tlp5 stp tlp5 \ 
    add tlp6 stp tlp6 \ 
    add tlp7 stp tlp7 \ 
    up

SEE ALSO

bridge(4), pf(4), ifconfig.if(5), ifconfig(8), ipf(8), pfil(9)

HISTORY

The brconfig utility first appeared in NetBSD 1.6.

AUTHORS

The bridge(4) driver and brconfig utility were originally written by Jason L. Wright <jason@thought.net> as part of an undergraduate independent study at the University of North Carolina at Greensboro.

This version of the brconfig utility was written from scratch by Jason R. Thorpe <thorpej@wasabisystems.com>.