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 infor-
mation 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
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 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 behav-
iour.
An example of how to setup a so called anonymous bridge (a bridge with-
out 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
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 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 ma-
chines 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 defin-
ition by using the "up" option. If however you still want to use multi-
ple 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/net-
work/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 fol-
low 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) in-
terfaces 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 fractional part.
bridge_hello time
set hello time to time seconds, default is 2, can have a frac-
tional 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 recom-
mended way of doing this.
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 for-
warding 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, af-
fects 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_token token
set IPv6 tokenized interface identifier for the bridge to token,
see ip-token(8) for more info on this.
bridge_vlan_aware yes/no
specify if the bridge is vlan aware an thus needs vlan filtering
to be activated or not.
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.
FILES
/etc/network/interfaces
definitions of network interfaces See interfaces(5) for more in-
formation.
KNOWN BUGS/LIMITATIONS
The default values shown here are current values as of this writ-
ing, 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@debian.org>
based on interfaces(5).
SEE ALSO
brctl(8), interfaces(5), ifup(8), ip-token(8), iwconfig(8),
run-parts(8).
bridge-utils January 13 2008 BRIDGE-UTILS-INTERFACES(5)
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