Bridges with Linux
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Contents
Bridge Utilities in Linux
The bridge-utils package
Installation:
$ sudo apt-get install bridge-utils
Commands:
$ dpkg -L bridge-utils | grep bin /usr/sbin /usr/sbin/brctl
Configuration files:
$ dpkg -L bridge-utils | grep etc /etc /etc/network /etc/network/if-pre-up.d /etc/network/if-pre-up.d/bridge /etc/network/if-post-down.d /etc/network/if-post-down.d/bridge
Resources:
The bridge control command 'brctl'
Show the bridges:
$ brctl show
bridge name bridge id STP enabled interfaces
br0 8000.001601a1a9b7 no eth0
wlan0
br1 8000.000000000000 no
Create a new bridge:
$ brctl addbr br1
Add/delete interfaces a un bridge:
$ brctl delif
$ brctl addif
Creation of a bridge
We install the package bridge-utils and the file /etc/network/interfaces. Then we create an interface as a bridge from eth0:
$ cat /etc/network/interfaces auto lo iface lo inet loopback auto br0 iface br0 inet static address 192.168.1.2 netmask 255.255.255.0 gateway 192.168.1.1 bridge_ports eth0 auto eth0 iface eth0 inet manual
We can use DHCP, as well:
$ cat /etc/network/interfaces auto lo iface lo inet loopback auto br0 iface br0 inet dhcp bridge_ports eth0 auto eth0 iface eth0 inet manual
NOTE: Note how the interface eth0 is manually configured and the line bridge_ports eth0.
We restart to initialize the network:
$ sudo /etc/init.d/networking restart
From now on the eth0 interface can be observed by executing ifconfig:
$ ifconfig
br0 Link encap:Ethernet HWaddr 00:30:1B:B7:CD:B6
inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::230:1bff:feb7:cdb6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:28932 errors:0 dropped:0 overruns:0 frame:0
TX packets:28277 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:24356075 (23.2 MB) TX bytes:17213164 (16.4 MB)
eth0 Link encap:Ethernet HWaddr 00:30:1B:B7:CD:B6
inet6 addr: fe80::230:1bff:feb7:cdb6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:20788 errors:0 dropped:0 overruns:0 frame:0
TX packets:14681 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:23664360 (22.5 MB) TX bytes:1995733 (1.9 MB)
Interrupt:20
It is a non configured interface (Dummy). This is normal, check the network if it still works.
The package uml-utilities
Installation of User Mode Linux utilities package (uml-utilities):
$ sudo apt-get install uml-utilities
The User Mode Linux package contains tools to create TAP interfaces. Add permissions to access the user interface:
$ sudo gpasswd -a <user> uml-net
For example:
$ sudo gpasswd -a sergi uml-net
We need to restart to apply the permissions.
We edit the file /etc/network/interfaces To add the TAP interface by appending:
auto tap0
iface tap0 inet manual
up ifconfig $IFACE 0.0.0.0 up
down ifconfig $IFACE down
tunctl_user <user>
We replace the placeholer <user> with out username. For example:
auto tap0
iface tap0 inet manual
up ifconfig $IFACE 0.0.0.0 up
down ifconfig $IFACE down
tunctl_user sergi
bridge_ports eth0 tap0
Restart to initialize the network:
$ sudo /etc/init.d/networking restart
The command tunctl
Now we create a bridge:
$ sudo tunctl -t tap1 -u sergi $ sudo chmod 666 /dev/net/tun
And:
$ sudo brctl addbr br0
$ sudo ifconfig eth0 0.0.0.0 promisc $ sudo brctl addif br0 eth0 $ dhclient br0
$ sudo brctl addif br0 tap1
