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       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. These ports
       are the interfaces that are part of the bridge, and they shouldn’t have
       any stanzas defining them on  the  interfaces  file.  Other  extensions
       allow you to tune the bridge options or change a bridge behaviour.

       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).