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BRIDGE-UTILS-INTERFACES(5)                 File formats                BRIDGE-UTILS-INTERFACES(5)



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

DESCRIPTION
       /etc/network/interfaces  contains  network  interface  configuration  information  for the
       ifup(8) and ifdown(8) commands.  This manpage describes the bridge extensions to the stan‐
       dard 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
           address 192.168.1.2
           network 192.168.1.0
           netmask 255.255.255.0
           broadcast 192.168.1.255
           gateway 192.168.1.1
           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 sta‐
       tus, and by default, they will wait for the bridge to get there, or for the estimated max‐
       imum  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
           address 192.168.1.2
           network 192.168.1.0
           netmask 255.255.255.0
           broadcast 192.168.1.255
           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  wire‐
       less_* 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 http://bugs.debian.org/319832

IFACE OPTIONS
       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 syn‐
              tax (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
              part.

       bridge_gcint time
              set garbage collection interval to time seconds, default is 4,  can  have  a  frac‐
              tional 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 the bridge to the specified one.  There were some
              concerns of how this was done in the past, see:  http://bugs.debian.org/271406  but
              we   are   doing   it   on   a   new  way  now  that  shouldn't  be  as  bad,  see:
              http://bugs.debian.org/725786 however you should know what  you  are  doing  before
              using this option.

       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  inter‐
              face 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. Speci‐
              fying no ports here should  not  be  used  if  we  are  using  regex  or  "all"  on
              bridge_ports, as it wouldn't work.

FILES
       /etc/network/interfaces
              definitions of network interfaces See interfaces(5) for more information.


       KNOWN BUGS/LIMITATIONS
              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.

AUTHOR
       This manpage was written by Santiago Garcia Mantinan <manty AT debian.org>  based  on  inter‐
       faces(5).

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



bridge-utils                             January 13 2008               BRIDGE-UTILS-INTERFACES(5)


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