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>Linux BRIDGE-STP-HOWTO: About The Linux Modular Bridge And STP</TH
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="SET-UP-THE-BRIDGE"
>6. Set Up The Bridge</A
></H1
><P
>Make sure all your network cards are working nicely
and are accessible.
If so, <B
CLASS="COMMAND"
>ifconfig</B
> will show you the hardware layout
of the network-interface.
If you have problems making your cards work please read the
Ethernet-HOWTO at
<A
HREF="http://www.linuxdoc.org/HOWTO/Ethernet-HOWTO.html"
TARGET="_top"
>http://www.linuxdoc.org/HOWTO/Ethernet-HOWTO.html</A
>.
Don't mess around with IP-addresses or net-masks.
You will not need it, until you bridge fully operational an up.
</P
><P
>After you did the steps mentioned above a
<B
CLASS="COMMAND"
>modprobe -v bridge</B
> should show no errors.
You can check the success by issuing a
<B
CLASS="COMMAND"
>cat /proc/modules</B
>.
Also for each of the network cards you want to use in the bridge
the <B
CLASS="COMMAND"
>ifconfig <TT
CLASS="USERINPUT"
><B
>whateverNameYourInterfaceHas</B
></TT
></B
>
should give you some information about the interface.
</P
><P
>If your <SPAN
CLASS="APPLICATION"
>bridge-utilities</SPAN
> have been
correctly built and your kernel and bridge-module are OK, then
issuing a <B
CLASS="COMMAND"
>brctl</B
> should show a small command
synopsis.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="BRCTL-SYNOPSIS"
>6.1. <B
CLASS="COMMAND"
>brctl</B
> Command Synopsis</A
></H2
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # brctl
commands:
addbr <bridge> add bridge <A
NAME="BRCTL-ADDBR"
><IMG
SRC="../images/callouts/1.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(1)"></A
>
addif <bridge> <device> add interface to bridge <A
NAME="BRCTL-ADDIF"
><IMG
SRC="../images/callouts/2.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(2)"></A
>
delbr <bridge> delete bridge <A
NAME="BRCTL-DELBR"
><IMG
SRC="../images/callouts/3.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(3)"></A
>
delif <bridge> <device> delete interface from bridge <A
NAME="BRCTL-DELIF"
><IMG
SRC="../images/callouts/4.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(4)"></A
>
show show a list of bridges <A
NAME="BRCTL-SHOW"
><IMG
SRC="../images/callouts/5.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(5)"></A
>
showbr <bridge> show bridge info <A
NAME="BRCTL-SHOWBR"
><IMG
SRC="../images/callouts/6.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(6)"></A
>
showmacs <bridge> show a list of mac addrs <A
NAME="BRCTL-SHOWMACS"
><IMG
SRC="../images/callouts/7.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(7)"></A
>
setageing <bridge> <time> set ageing time <A
NAME="BRCTL-SETAGEING"
><IMG
SRC="../images/callouts/8.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(8)"></A
>
setbridgeprio <bridge> <prio> set bridge priority <A
NAME="BRCTL-SETBRIDGEPRIO"
><IMG
SRC="../images/callouts/9.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(9)"></A
>
setfd <bridge> <time> set bridge forward delay <A
NAME="BRCTL-SETFD"
><IMG
SRC="../images/callouts/10.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(10)"></A
>
setgcint <bridge> <time> set garbage collection interval <A
NAME="BRCTL-SETGCINT"
><B
>(11)</B
></A
>
sethello <bridge> <time> set hello time <A
NAME="BRCTL-SETHELLO"
><B
>(12)</B
></A
>
setmaxage <bridge> <time> set max message age <A
NAME="BRCTL-SETMAXAGE"
><B
>(13)</B
></A
>
setpathcost <bridge> <port> <cost> set path cost <A
NAME="BRCTL-SETPATHCOST"
><B
>(14)</B
></A
>
setportprio <bridge> <port> <prio> set port priority <A
NAME="BRCTL-SETPORTPRIO"
><B
>(15)</B
></A
>
stp <bridge> <state> {dis,en}able stp <A
NAME="BRCTL-STP"
><B
>(16)</B
></A
>
</PRE
></TD
></TR
></TABLE
>
</P
><DIV
CLASS="CALLOUTLIST"
><DL
COMPACT="COMPACT"
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-ADDBR"
><IMG
SRC="../images/callouts/1.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(1)"></A
><A
HREF="set-up-the-bridge.html#BRCTL-DELBR"
><IMG
SRC="../images/callouts/3.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(3)"></A
></DT
><DD
>The
<B
CLASS="COMMAND"
>brctl addbr <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
></B
>
command creates a logical bridge instance with the name
<TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
>.
You will need at least one logical instance to do any bridging at
all.
You can interpret the logical bridge being a container for the
interfaces taking part in the bridging.
Each bridging instance is represented by a new network interface.
</DD
><DIV
CLASS="EXAMPLE"
><A
NAME="CREATE-A-INSTANCE"
></A
><P
><B
>Example 6. Creating A Instance</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # brctl addbr mybridge1
</PRE
></TD
></TR
></TABLE
></DIV
><DD
><P
>The corresponding <SPAN
CLASS="QUOTE"
>"shutdown"</SPAN
> command is
<B
CLASS="COMMAND"
>brctl delbr <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
></B
>.
<DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
><B
CLASS="COMMAND"
>brctl delbr <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
></B
>
will only work, if there are no more interfaces added to the
instance you want to delete.
</P
></TD
></TR
></TABLE
></DIV
>
</P
></DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-ADDIF"
><IMG
SRC="../images/callouts/2.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(2)"></A
><A
HREF="set-up-the-bridge.html#BRCTL-DELIF"
><IMG
SRC="../images/callouts/4.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(4)"></A
></DT
><DD
>The
<B
CLASS="COMMAND"
>brctl addif <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
>
<TT
CLASS="USERINPUT"
><B
>device</B
></TT
></B
>
command enslaves the network device <TT
CLASS="USERINPUT"
><B
>device</B
></TT
>
to take part in the bridging of <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
>.
As a simple explanation, each interface enslaved into a instance
is bridged to the other interfaces of the instance.
</DD
><DD
><P
>The corresponding command to tale a interface out of the bridge
would be
<B
CLASS="COMMAND"
>brctl delif <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
>
<TT
CLASS="USERINPUT"
><B
>device</B
></TT
></B
>
</P
></DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SHOW"
><IMG
SRC="../images/callouts/5.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(5)"></A
></DT
><DD
>The <B
CLASS="COMMAND"
>brctl show</B
> command gives you a summary
about the overall bridge status, and the instances running as
shown in <A
HREF="set-up-the-bridge.html#BRCTL-SHOW-OUTPUT"
>Example 7</A
>.
If you are interested in detailed information about a instance and
it's interfaces you will have to check <A
HREF="set-up-the-bridge.html#BRCTL-SHOWBR"
><A
HREF="set-up-the-bridge.html#BRCTL-SHOWBR"
><IMG
SRC="../images/callouts/6.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(6)"></A
></A
>.
</DD
><DIV
CLASS="EXAMPLE"
><A
NAME="BRCTL-SHOW-OUTPUT"
></A
><P
><B
>Example 7. Output Of <B
CLASS="COMMAND"
>brctl show</B
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # brctl show
bridge name bridge id stp enabled
mybridge1 0000.0800062815f6 yes
</PRE
></TD
></TR
></TABLE
></DIV
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SHOWBR"
><IMG
SRC="../images/callouts/6.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(6)"></A
></DT
><DD
>The <B
CLASS="COMMAND"
>brctl showbr <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
></B
>
command gives you a summary about a bridge instance and it's enslaved
interfaces.
</DD
><DIV
CLASS="EXAMPLE"
><A
NAME="BRCTL-SHOWBR-OUTPUT"
></A
><P
><B
>Example 8. Output Of <B
CLASS="COMMAND"
>brctl showbr <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
></B
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # brctl showbr mybridge1
mybridge1
bridge id 0000.0800062815f6
designated root 0000.0800062815f6
root port 0 path cost 0
max age 4.00 bridge max age 4.00
hello time 1.00 bridge hello time 1.00
forward delay 4.00 bridge forward delay 4.00
ageing time 300.00 gc interval 4.00
hello timer 0.84 tcn timer 0.00
topology change timer 0.00 gc timer 1.84
flags
eth0 (1)
port id 8001 state forwarding
designated root 0000.0800062815f6 path cost 100
designated bridge 0000.0800062815f6 message age timer 0.00
designated port 8001 forward delay timer 0.00
designated cost 0 hold timer 0.84
flags
eth1 (2)
port id 8002 state forwarding
designated root 0000.0800062815f6 path cost 100
designated bridge 0000.0800062815f6 message age timer 0.00
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.84
flags
</PRE
></TD
></TR
></TABLE
></DIV
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SHOWMACS"
><IMG
SRC="../images/callouts/7.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(7)"></A
></DT
><DD
>The <B
CLASS="COMMAND"
>brctl showmacs <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
></B
>
command gives you a list of <SPAN
CLASS="ACRONYM"
>MAC</SPAN
>-addresses of the
interfaces which are enslaved in <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
>.
</DD
><DIV
CLASS="EXAMPLE"
><A
NAME="BRCTL-SHOWMACS-OUTPUT"
></A
><P
><B
>Example 9. Output Of <B
CLASS="COMMAND"
>brctl showmacs <TT
CLASS="USERINPUT"
><B
>bridgename</B
></TT
></B
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # brctl showmacs mybridge1
port no mac addr is local? ageing timer
1 00:10:4b:b6:c6:e4 no 119.25
1 00:50:04:43:82:85 no 0.00
1 00:50:da:45:45:b1 no 76.75
1 00:a0:24:d0:4c:d6 yes 0.00
1 00:a0:24:f0:22:71 no 5.81
1 08:00:09:b5:dc:41 no 22.22
1 08:00:09:fb:39:a1 no 27.24
1 08:00:09:fc:92:2c no 53.13
4 08:00:09:fc:d2:11 yes 0.00
1 08:00:09:fd:23:88 no 230.42
1 08:00:09:fe:0d:6f no 144.55
</PRE
></TD
></TR
></TABLE
></DIV
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETAGEING"
><IMG
SRC="../images/callouts/8.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(8)"></A
></DT
><DD
>Sets the aging time.
The aging time is the number of seconds a <SPAN
CLASS="ACRONYM"
>MAC</SPAN
>-address will be
kept in the forwarding database after having received a packet
from this <SPAN
CLASS="ACRONYM"
>MAC</SPAN
> address.
The entries in the forwarding database are periodically timed out
to ensure they won't stay around forever.
Normally there should be no need to modify this parameter.
</DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETBRIDGEPRIO"
><IMG
SRC="../images/callouts/9.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(9)"></A
></DT
><DD
>Sets the bridge's relative priority.
The bridge with the lowest priority will be elected as the root
bridge.
The root bridge is the <SPAN
CLASS="QUOTE"
>"central"</SPAN
> bridge in the
spanning tree.
More information about <SPAN
CLASS="ACRONYM"
>STP</SPAN
> you find at
<A
HREF="advanced-bridge.html#STP"
>Section 7.1</A
>.
</DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETFD"
><IMG
SRC="../images/callouts/10.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(10)"></A
></DT
><DD
>Sets the forwarding delay time.
The forwarding delay time is the time spent in each of the
Listening and Learning states before the Forwarding state is
entered.
</DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETGCINT"
><B
>(11)</B
></A
></DT
><DD
>Sets the garbage collection interval.
Every (this number) seconds, the entire forwarding database is
checked for timed-out entries.
The timed-out entries are removed.
</DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETHELLO"
><B
>(12)</B
></A
></DT
><DD
>Sets the hello time.
Every (this number) seconds, a hello packet is sent out by the Root
Bridge and the Designated Bridges.
Hello packets are used to communicate information about the topology
throughout the entire Bridged Local Area Network.
More information about <SPAN
CLASS="ACRONYM"
>STP</SPAN
> you find at
<A
HREF="advanced-bridge.html#STP"
>Section 7.1</A
>.
</DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETMAXAGE"
><B
>(13)</B
></A
></DT
><DD
>Sets the maximum message age.
If the last seen (received) hello packet is more than this number
of seconds old, the bridge in question will start the takeover
procedure in attempt to become the Root Bridge itself.
More information about <SPAN
CLASS="ACRONYM"
>STP</SPAN
> you find at
<A
HREF="advanced-bridge.html#STP"
>Section 7.1</A
>.
</DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETPATHCOST"
><B
>(14)</B
></A
></DT
><DD
>Sets the cost of receiving (or sending, I'm not sure) a packet
on this interface.
Faster interfaces should have lower path costs.
These values are used in the computation of the minimal spanning
tree.
More information about <SPAN
CLASS="ACRONYM"
>STP</SPAN
> you find at
<A
HREF="advanced-bridge.html#STP"
>Section 7.1</A
>.
Paths with lower costs are likelier to be used in the spanning tree
than high-cost paths
(As an example, think of a gigabit line with a 100Mbit or 10Mbit
line as a backup line.
You don't want the 10/100Mbit line to become the primary line there.)
</DD
><DD
><P
> The Linux implementation currently sets the path cost of all eth*
interfaces to 100, the nominal cost for a 10Mbit connection. There is
unfortunately no easy way to discern 10Mbit from 100Mbit from 1Gbit
Ethernet cards, so the bridge cannot use the real interface speed.
</P
></DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-STP"
><B
>(16)</B
></A
></DT
><DD
>With this parameter you can enable or disable the Spanning Tree
Protocol.
</DD
><DT
><A
HREF="set-up-the-bridge.html#BRCTL-SETBRIDGEPRIO"
><IMG
SRC="../images/callouts/9.gif"
HSPACE="0"
VSPACE="0"
BORDER="0"
ALT="(9)"></A
><A
HREF="set-up-the-bridge.html#BRCTL-SETHELLO"
><B
>(12)</B
></A
><A
HREF="set-up-the-bridge.html#BRCTL-SETPATHCOST"
><B
>(14)</B
></A
><A
HREF="set-up-the-bridge.html#BRCTL-STP"
><B
>(16)</B
></A
></DT
><DD
>This parameters are only of interest, if you have more than
one bridge in your LAN and stp enabled.
Before modifying them you should read
<A
HREF="advanced-bridge.html#STP"
>Section 7.1</A
>.
</DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="BASIC-SETUP"
>6.2. Basic Setup</A
></H2
><P
>The standard configuration should consist of:
</P
><P
></P
><OL
COMPACT="COMPACT"
TYPE="1"
><LI
><P
>Create the bridge interface.
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # brctl addbr mybridge
</PRE
></TD
></TR
></TABLE
>
</P
></LI
><LI
><P
>Add interfaces to the bridge.
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # brctl addif mybridge eth0
root@mbb-1:~ # brctl addif mybridge eth1
</PRE
></TD
></TR
></TABLE
>
</P
></LI
><LI
><P
>Zero IP the interfaces.
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # ifconfig eth0 0.0.0.0
root@mbb-1:~ # ifconfig eth1 0.0.0.0
</PRE
></TD
></TR
></TABLE
>
</P
></LI
><LI
><P
>Put up the bridge.
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # ifconfig mybridge up
</PRE
></TD
></TR
></TABLE
>
</P
></LI
><LI
><P
>Optionally you can configure the virtual interface
<TT
CLASS="USERINPUT"
><B
>mybridge</B
></TT
> to take part in your network.
It behaves like one interface (like a normal network card).
Exactly that way you configure it, replacing the previous
command with something like:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # ifconfig mybridge 192.168.100.5 netmask 255.255.255.0 up
</PRE
></TD
></TR
></TABLE
>
</P
></LI
></OL
><P
>A more sophisticated setup script you will find at
<A
HREF="practical-example.html#BRIDGE-INIT-SCRIPT"
>Example 16</A
>.
</P
><DIV
CLASS="IMPORTANT"
><BLOCKQUOTE
CLASS="IMPORTANT"
><P
><B
>Important: </B
>If you get the terrible experience of a frozen system or
some nasty behavior of your nicely shaped linux box at
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # ifconfig eth<TT
CLASS="USERINPUT"
><B
>n</B
></TT
> 0 0.0.0.0
</PRE
></TD
></TR
></TABLE
>
please try (after the reboot of the system if necessary)
before starting any bridge stuff at all a
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>root@mbb-1:~ # ifconfig eth<TT
CLASS="USERINPUT"
><B
>n</B
></TT
> promisc up
</PRE
></TD
></TR
></TABLE
>
If again your system is frozen it's you NIC's driver you have to blame,
not the bridging code.
</P
></BLOCKQUOTE
></DIV
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
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