Connecting Two Remote Local Networks With Transparent Bridging Technique
- Posted in: Networks
Both sample networks in this article need to have one *nix server for bridging. Our networks can be connected by any possible hardware that provides IP connection between them.
Short description: In described configuration we are connecting two remote LANs to make them appearing as one network with 192.168.1.0/24 address space (however physically, presense of bridges in network configuration is not affecting IP protocol and is fully transparent for it, so you can freely select any address space). Both of the bridging servers has two network interfaces: one (as eth0 in our example) connested to the LAN, and second (eth1) is being used as transport to connect networks. When ethernet tunnel between gateways in both networks will be bringed up we will connect tunnel interfaces with appropriate LAN interfaces with bridge interfaces. Schematically this configuration can be following:
+-------+ +-------+
| br0 | | br0 |
+-------+ +-------+
| | | |
Network 1 | | | | Network 2
----------eth0 tap0---eth1........eth1---tap0 eth0---------------
Setting Up Bridging Servers
Notice: This article describes Debian GNU/Linux servers setup. If you are using another distribution, there can be some differences in network configuration and package management, but the main idea of described actions will be the same.
First of all, we need to check if tun and bridge modules is not included in current kernel. If they are not includen, we need to rebuild kernel with CONFIG_TUN and CONFIG_BRIDGE options.
Next, we need to create tunnel device file for our tunnel:
# cd /dev
# ./MAKEDEV tun
# mkdir misc
# ln -s /dev/net /dev/misc/net
Notice: Last command is needed to make vtun work, because authors build for debian is looking for tunnel device driver at /dev/misc/net/tun.
To create ethernet tunnel between bridging servers we will use vtun software. Debian package (and also source code and other OS packages) can be loaded from authors site.
When package file vtun_X.Y-Z_i386.deb will be downloaded, we will need to install all required packages:
# apt-get install bridge-utils ebtables iptables libssl0.9.6
...
# dpkg -i vtun_X.Y-Z_i386.deb
When vtun will be installed, we will need to select one of the bridging servers as master and second server will be slave and appropriately change vtund-start.conf and vtund.conf file in /etc/ on buth servers. Complete config files for master is following.
/etc/vtund-start.conf
----cut-here------------------------------------ --server-- 5000 ----cut-here------------------------------------
/etc/vtund.conf
----cut-here------------------------------------
options {
port 5000; # Listen on this port.
# Syslog facility
syslog daemon;
# Path to various programs
ifconfig /sbin/ifconfig;
route /sbin/route;
firewall /sbin/iptables;
ip /sbin/ip;
}
default {
compress no;
encrypt no;
speed 0;
}
rembridge {
passwd Pa$$Wd;
type ether;
proto udp;
keepalive yes;
compress no;
encrypt yes;
up {
# Connection is Up
ifconfig "%% up";
program "brctl addif br0 %%";
};
down {
# Connection is Down
ifconfig "%% down";
};
}
----cut-here------------------------------------
Slave server config files is following:
/etc/vtund-start.conf
----cut-here------------------------------------ rembridge 10.1.1.1 -p ----cut-here------------------------------------
Notice: In this example 10.1.1.1 is transport address of master server.
/etc/vtund.conf
----cut-here------------------------------------
options {
# Path to various programs
ifconfig /sbin/ifconfig;
route /sbin/route;
firewall /sbin/iptables;
}
korsar {
pass Pa$$Wd; # Password
type ether; # Ethernet tunnel
up {
# Connection is Up
ifconfig "%% up";
program "brctl addif br0 %%"
};
down {
# Connection is Down
ifconfig "%% down";
};
}
----cut-here------------------------------------
To bring up bridge between LAN ethernet interface and our newly created tunnel interface we need to create bridge interface. To complete this task we will add br0 interface description to /etc/network/interfaces file:
auto br0
iface br0 inet static
address 192.168.1.199
netmask 255.255.255.0
bridge_ports eth0
Notice: IP-addresses on both sides of our bridge must be unique in both networks. eth0 is LAN interface.
Now, we need to bring this interface up:
# ifup br0
When br0 interface will be created, we will be able to start vtun.
# /etc/init.d/vtund restart
If everything was done correctly, we will see following results on both sersers (br0 and tap0 interfaces):
# ifconfig tap0
tap0 Link encap:Ethernet HWaddr 00:FF:B2:91:CA:DE
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:701818 errors:0 dropped:0 overruns:0 frame:0
TX packets:405939 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:975889241 (930.6 MiB) TX bytes:44704104 (42.6 MiB)
# ifconfig br0
br0 Link encap:Ethernet HWaddr 00:02:44:2A:03:30
inet addr:192.168.1.199 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2660 errors:0 dropped:0 overruns:0 frame:0
TX packets:42 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:239368 (233.7 KiB) TX bytes:2338 (2.2 KiB)
#
If we need to see current state of bridge interface, we can use brctl tool:
# brctl show br0
bridge name bridge id STP enabled interfaces
br0 8000.0002442a0330 no eth0
tap0
#
When all of described steps will be completed, our computers in both networks will be able to communicate with each other. IP addresses on bridge interfaces can be used for troubleshooting network connection. And last, if you need, you can turn on compression or enrtyption of data within created tunnel.