Provided by: bridge-utils_1.7-1ubuntu3_amd64 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 format.

       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
           pre-up ip addr flush dev eth0
       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 and we add a pre-up command to remove all addresses on eth0 as this interface had an
       address set up before (needed only on weird/broken setups).

       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 at


       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

              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.* em.* p[0-9].* noregex" and will get all
              the ethX and biosdevname-format (emX and pX) 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 root.

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

       bridge_gcint time
              set  garbage  collection  interval  to  time  seconds,  default  is  4,  can have a
              fractional part.  Available on Linux kernel versions < 2.6.0.

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

       bridge_hw MAC_address|interface
              set the Ethernet MAC address of the bridge to the specified one or to  the  address
              of  the  specified interface.  There were some concerns of how this was done in the
              past but we are doing it on a new way now, it is currently not only considered safe
              but  also  necessary  or  recommended  in  a  lot  of  scenarios  like  IPv6,  DHCP
              reservations, ... the ussage of bridge_hw setting if the recommended way  of  doing

       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, from 1 to 65535, default is 100, port is the name of the
              interface to which this setting applies.

       bridge_portprio port priority
              set port priority, from 0 (max) to 63 (min), default is 32, 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. Setting stp to on will cause  IPv6
              address to be lost, see:

       bridge_vlan_aware yes/no
              specify if the bridge is vlan aware an thus needs vlan filtering to be activated or

       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 information.

              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


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