Provided by: bridge-utils_1.4-3_i386 bug


       bridge-utils-interfaces - bridge-utils extensions for the interfaces(5)
       file format


       /etc/network/interfaces  contains   network   interface   configuration
       information  for  the  ifup(8)  and  ifdown(8)  commands.  This manpage
       describes the bridge extensions  to  the  standard  interfaces(5)  file

       The  main  extension  is  the bridge_ports option, with it you describe
       that the interface is a bridge and  what  ports  does  it  have.  Other
       extensions  allow  you  to  tune  the bridge options or change a bridge

       We’ll see this with an example:

              auto br0
              iface br0 inet static
                  bridge_ports all

       Well, after setting this, an ifup br0, or the next reboot,  should  let
       you have a bridge up and running, after waiting for the ports to get to
       the forwarding status, of course. This bridge will be  using  all  your
       ethX interfaces, as we have stated on the bridge_ports line.

       The  Debian bridge setup scripts will wait for it to get ready to work.
       They do this by trying to guess the maximum time that the  bridge  will
       need  to  get  to the forwarding status, and by default, they will wait
       for the bridge to get there, or for the estimated maximum  time  to  go
       by.  This is done so that the services that are loaded after the bridge
       setup have a working network  interface  and  don’t  fail  because  the
       bridge  is  still not working. See bridge_maxwait if you want to change
       this behaviour.

       An example of how to setup a  so  called  anonymous  bridge  (a  bridge
       without an assigned IP) would look like this:

              iface br1 inet manual
                   bridge_ports eth1 eth2
                   bridge_maxwait 0

       Here  we  select the interfaces eth1 and eth2 to be added to the bridge
       interface br1, which will be an anonymous  bridge,  we  also  tell  the
       scripts  not to wait, as we won’t be having any service running on that
       interface (it doesn’t even have an IP).

       An example of a little more complex bridge setup could be:

              auto br0
              iface br0 inet static
                  bridge_ports all weird0
                  bridge_bridgeprio 32767
                  bridge_portprio eth0 129
                  bridge_fd 5

       In this example we select all the eth* devices plus a weird  device  to
       be added to the bridge, also we change the bridge default priority to a
       higher one so that this bridge  becomes  the  root  (if  there  are  no
       bridges  with  higher  priority  on the net, that is) and also we lower
       priority of port eth0 so that it is not used if there are  other  ports
       with higher priority to reach the same destination, at the end we lower
       the default forward delay.

       If there is a need to set up any of the interfaces participating on the
       bridge  and not the bridge itself, then we must add the commands to set
       up those settings in a "pre-up" or "up" statement. This means  that  if
       we  have a wireless card that we want to add to a bridge and we want to
       set it to master, and select the essid, instead of  using  the  typical
       wireless_*  commands  we  could  add to the bridge definition something
       like this:

              pre-up iwconfig wlan0 mode master essid myESSID

       Be aware, however, that using wireless cards as part of a bridge is not
       a  good  idea  if  the card belonging to the bridge is in managed mode.
       Trying to bridge packets coming out of our LAN through a wireless  card
       that is set in managed mode (the card is a client of an AP) is bound to
       give problems, as the AP will probably refuse packets with  source  MAC
       addresses  which  are  not  associated  (this will be the case of other
       machines going through the wireless card of the bridge into the AP).

       Multiple stanzas of a bridge definition are currently not supported, so
       if  you  want  to  add  a  ipv6 and a ipv4 to a bridge do it all in one
       definition by using the "up" option. If however you still want  to  use
       multiple  stanzas or would like to read more on this bug you can see it


       A  little  explanation  on  the  new  options  that  can  be  used   on
       /etc/network/interfaces  to  setup  the bridge, so you don’t have to go
       and look at the scripts...

       bridge_ports interface specification
              this option must exist for the scripts to setup the bridge, with
              it  you specify the ports you want to add to your bridge, either
              using "none" if you want a bridge without any interfaces or  you
              want  to add them later using brctl, or a list of the interfaces
              you want to add separated by spaces, for example:

                     bridge_ports eth0 eth4

              You should not put any lines to configure  the  interfaces  that
              will  be used by the bridge, as this will be setup automatically
              by the scripts when bringing the bridge up.

              If you need to specify the interfaces more flexibly, you can use
              the following syntax (most useful on a Xen dom0):

                     bridge_ports regex (eth|vif).*

              This  means  to  evaluate  (as in egrep(1)) the expressions that
              follow after  "regex"  until  either  the  end  or  a  "noregex"
              statement  is  reached.   The  regular expressions are evaluated
              against all local interfaces and those that match are added.

              Specifying "all" is short for "regex eth.* noregex" and will get
              all the ethX interfaces added to the bridge.

              Carrying this to the extremes, the following is valid syntax:

                     bridge_ports all regex if.0 noregex ext0 regex vif.*

              This will add all ethX interfaces, the ifX0 interfaces, the ext0
              interface and all vifX interfaces.

       bridge_ageing time
              set ageing time, default is 300, can have a fractional part.

       bridge_bridgeprio priority
              set bridge priority, priority is between 0 and 65535, default is
              32768,  affects  bridge  id,  lowest priority bridge will be the

       bridge_fd time
              set bridge forward delay to time seconds,  default  is  15,  can
              have a fractional part.

       bridge_gcint time
              set  garbage  collection interval to time seconds, default is 4,
              can have a fractional part.

       bridge_hello time
              set hello time to  time  seconds,  default  is  2,  can  have  a
              fractional part.

       bridge_hw MAC address
              set the Ethernet MAC address of all the bridge interfaces to the
              specified one so that the bridge ends up  having  this  hardware
              address as well. WARNING: use this only if you know what you are
              doing, changing the MAC address of the cards may  cause  trouble
              if  you  don’t  know  what  you are doing. To see the discussion
              about this feature and the problems that can cause you  can  try
              to  have  a look at the bug that asked for this feature visiting

       bridge_maxage time
              set max message age to time seconds, default is 20, can  have  a
              fractional part.

       bridge_maxwait time
              forces  to  time seconds the maximum time that the Debian bridge
              setup scripts will wait for the  bridge  ports  to  get  to  the
              forwarding  status, doesn’t allow factional part. If it is equal
              to 0 then no waiting is done.

       bridge_pathcost port cost
              set path cost for a port, default is 100, port is  the  name  of
              the interface to which this setting applies.

       bridge_portprio port priority
              set  port priority, default is 128, affects port id, port is the
              name of the interface to which this setting applies.

       bridge_stp state
              turn spanning tree protocol on/off, state values are on  or  yes
              to  turn  stp  on and any other thing to set it off, default has
              changed to off for security reasons in latest  kernels,  so  you
              should  specify  if you want stp on or off with this option, and
              not rely on your kernel’s default behaviour.

       bridge_waitport time [ports]
              wait for a max of time seconds for the specified ports to become
              available,  if  no  ports  are specified then those specified on
              bridge_ports will be used here. Specifying no ports here  should
              not  be  used if we are using regex or "all" on bridge_ports, as
              it wouldn’t work.


              definitions of network interfaces  See  interfaces(5)  for  more

              The  default  values  shown  here  are current values as of this
              writing, but as they are not related to this package but to  the
              bridge code itself, can change anytime.


       This manpage was written by Santiago Garcia Mantinan <>
       based on interfaces(5).


       brctl(8), interfaces(5), ifup(8), iwconfig(8), run-parts(8).