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NAME | SYNOPSIS | DESCRIPTION | INSTANCES | PORTS | AGEING | SPANNING TREE PROTOCOL | NOTES | SEE ALSO | AUTHOR | COLOPHON |
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BRCTL(8) BRCTL(8)
brctl - ethernet bridge administration
brctl [command]
brctl is used to set up, maintain, and inspect the ethernet
bridge configuration in the Linux kernel.
An ethernet bridge is a device commonly used to connect different
networks of ethernets together, so that these ethernets will
appear as one ethernet to the participants.
Each of the ethernets being connected corresponds to one physical
interface in the bridge. These individual ethernets are bundled
into one bigger ('logical') ethernet, this bigger ethernet
corresponds to the bridge network interface.
The command brctl addbr <name> creates a new instance of the
ethernet bridge. The network interface corresponding to the
bridge will be called <name>.
The command brctl delbr <name> deletes the instance <name> of the
ethernet bridge. The network interface corresponding to the
bridge must be down before it can be deleted!
The command brctl show shows all current instances of the
ethernet bridge.
Each bridge has a number of ports attached to it. Network traffic
coming in on any of these ports will be forwarded to the other
ports transparently, so that the bridge is invisible to the rest
of the network (i.e. it will not show up in traceroute(8) ).
The command brctl addif <brname> <ifname> will make the interface
<ifname> a port of the bridge <brname>. This means that all
frames received on <ifname> will be processed as if destined for
the bridge. Also, when sending frames on <brname>, <ifname> will
be considered as a potential output interface.
The command brctl delif <brname> <ifname> will detach the
interface <ifname> from the bridge <brname>.
The command brctl show <brname> will show some information on the
bridge and its attached ports.
The bridge keeps track of ethernet addresses seen on each port.
When it needs to forward a frame, and it happens to know on which
port the destination ethernet address (specified in the frame) is
located, it can 'cheat' by forwarding the frame to that port
only, thus saving a lot of redundant copies and transmits.
However, the ethernet address location data is not static data.
Machines can move to other ports, network cards can be replaced
(which changes the machine's ethernet address), etc.
brctl showmacs <brname> shows a list of learned MAC addresses for
this bridge.
brctl setageing <brname> <time> sets the ethernet (MAC) address
ageing time, in seconds. After <time> seconds of not having seen
a frame coming from a certain address, the bridge will time out
(delete) that address from the Forwarding DataBase (fdb).
brctl setgcint <brname> <time> sets the garbage collection
interval for the bridge <brname> to <time> seconds. This means
that the bridge will check the forwarding database for timed out
entries every <time> seconds.
Multiple ethernet bridges can work together to create even larger
networks of ethernets using the IEEE 802.1d spanning tree
protocol. This protocol is used for finding the shortest path
between two ethernets, and for eliminating loops from the
topology. As this protocol is a standard, Linux bridges will
interwork properly with other third party bridge products.
Bridges communicate with each other by sending and receiving
BPDUs (Bridge Protocol Data Units). These BPDUs can be recognised
by an ethernet destination address of 01:80:c2:00:00:00.
The spanning tree protocol can also be turned off (for those
situations where it just doesn't make sense, for example when
this Linux box is the only bridge on the LAN, or when you know
that there are no loops in the topology.)
brctl(8) can be used for configuring certain spanning tree
protocol parameters. For an explanation of these parameters, see
the IEEE 802.1d specification (or send me an email). The default
values should be just fine. If you don't know what these
parameters mean, you probably won't feel the desire to tweak
them.
brctl stp <bridge> <state> controls this bridge instance's
participation in the spanning tree protocol. If <state> is "on"
or "yes" the STP will be turned on, otherwise it will be turned
off. When turned off, the bridge will not send or receive BPDUs,
and will thus not participate in the spanning tree protocol. If
your bridge isn't the only bridge on the LAN, or if there are
loops in the LAN's topology, DO NOT turn this option off. If you
turn this option off, please know what you are doing.
brctl setbridgeprio <bridge> <priority> sets the bridge's
priority to <priority>. The priority value is an unsigned 16-bit
quantity (a number between 0 and 65535), and has no dimension.
Lower priority values are 'better'. The bridge with the lowest
priority will be elected 'root bridge'.
brctl setfd <bridge> <time> sets the bridge's 'bridge forward
delay' to <time> seconds.
brctl sethello <bridge> <time> sets the bridge's 'bridge hello
time' to <time> seconds.
brctl setmaxage <bridge> <time> sets the bridge's 'maximum
message age' to <time> seconds.
brctl setpathcost <bridge> <port> <cost> sets the port cost of
the port <port> to <cost>. This is a dimensionless metric.
brctl setportprio <bridge> <port> <priority> sets the port
<port>'s priority to <priority>. The priority value is an
unsigned 8-bit quantity (a number between 0 and 255), and has no
dimension. This metric is used in the designated port and root
port selection algorithms.
brctl(8) is obsolete. Some features such as STP guard, harpin
mode, fastleave and root block are intentionally not implemented
in this command. Instead use bridge command from iproute2
package for a more full set of features.
iptables(8)
Lennert Buytenhek <buytenh@gnu.org> Stephen Hemminger
<stephen@networkplumber.org>
This page is part of the bridge-utils (Ethernet bridge utilities)
project. Information about the project can be found at [unknown
-- if you know, please contact man-pages@man7.org] If you have a
bug report for this manual page, send it to bridge@osdl.org.
This page was obtained from the project's upstream Git repository
⟨git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/bridge-utils.git⟩
on 2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-06-23.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
November 7, 2001 BRCTL(8)
Pages that refer to this page: network_namespaces(7), brctl(8)
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