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BRCONFIG(8) NetBSD System Manager's Manual BRCONFIG(8)
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brconfig -- configure network bridge parameters
brconfig bridge command [args ...]
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 net-
works 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 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.
Remove the interface named by interface from the bridge. Promis-
cuous mode is disabled on the interface when it is removed from
addr Display the addresses that have been learned by the bridge.
Set the size of the bridge address cache to size. The default is
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.
Delete address from the address cache.
flush Delete all dynamically-learned addresses from the address cache.
Delete all addresses, including static addresses, from the
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.
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
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 npf(7). Other packet types are blocked.
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.
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.
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
Disable Spanning Tree protocol on interface. This is the default
for all interfaces added to a bridge.
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.
Set the time that must pass before an interface begins forwarding
packets when Spanning Tree is enabled. The default is 15 sec-
onds. The minimum is 1 second and the maximum is 255 seconds.
Set the time between broadcasting of Spanning Tree protocol con-
figuration messages. The default is 2 seconds. The minimum is 1
second and the maximum is 255 seconds.
Set the bridge priority for Spanning Tree. The default is 32768.
Allowed numerical values range from 0 (highest priority) to 65535
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.
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 configu-
ration could be used to implement a simple 802.11-to-Ethernet bridge
(assuming the 802.11 interface is in ad-hoc mode).
!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:
!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 \
bridge(4), pf(4), ifconfig.if(5), npf(7), ifconfig(8), pfil(9)
The brconfig utility first appeared in NetBSD 1.6.
The bridge(4) driver and brconfig utility were originally written by
Jason L. Wright <firstname.lastname@example.org> as part of an undergraduate indepen-
dent study at the University of North Carolina at Greensboro.
This version of the brconfig utility was written from scratch by
Jason R. Thorpe <email@example.com>.
NetBSD 9.99 July 19, 2020 NetBSD 9.99
Modified for NetBSD
by Kimmo Suominen