Layer 2 Dual Legged Switching Mode Example (DEPRECATED)

Note: This is example is deprecated, the "l2switch" configuration option will be removed with BalanceNG V3 (available Q2/2009).

This example shows how to set up BalanceNG as a transparent load balancing layer 2 (Ethernet) switch. You should change the example network "172.16.1.0/24" to match your own network setup (and the server address too of course). This example is fully operational with the free BalanceNG Basic License.

1. The initial network

Consider this to be the simple initial network configuration before inserting the BalanceNG node (the network 172.16.1.0/24 should represent a public allocated address space):

Figure 1: Network configuration without BalanceNG

What should be working:

• You should be able to ping the default gateway 172.16.1.254 from the Web Server.
• Clients from the Internet are able to initiate TCP connection to port 80 on the Web Server 172.16.1.10.

2. Load balancing transparently to two targets in switching mode

The key idea for BalanceNG in transparent switching mode is to connect two layer 2 areas with identical layer 3 network parameters. BalanceNG is configured to represent the old web server IP address 172.16.1.10, load balancing to the two targets ("virtual servers") 172.16.1.100 and 172.16.1.101. There's no need to change either the default gateway or the network parameters on the target machines to something else. BalanceNG needs its own address for ARP resolving, this is specified as "real" address in the network section.

Although this flavour of BalanceNG operation is very easy and simple to setup, it has one major disadvantage: High Availability (HA) with VRRP is not supported in Layer 2 Dual Legged Switching Mode operation of BalanceNG. This is because VRRP allows failover of "own" IP addresses from one node to another but does not offer any failover support of learned layer 2 MAC-Addresses of other machines (!).

This is how the new network looks like:

Figure 2: Network configuration with BalanceNG operating in "layer 2 dual legged switching mode"

The BalanceNG config file

This is the BalanceNG configuration for this example. The BalanceNG box needs two interfaces which are both member of the same layer 3 network. The "real" address in the network section is the source address for ARP resolving. Layer 2 switching mode has to be enabled with the "l2switch" configuration keyword.

//        configuration taken Tue Oct 10 16:43:01 2005
//        BalanceNG 1.391 (created 2005/08/15)
interface eth0
interface eth1
network   1 {
          name "local network"
          addr 172.16.1.0
          mask 255.255.255.0
          real 172.16.1.252
          interfaces eth0,eth1
}
register  network 1
enable    network 1
l2switch
server    1 {
          ipaddr 172.16.1.10 
          targets 1,2
          port 80
}
register  server 1
enable    server 1
target    1 {
          ipaddr 172.16.1.100 
          tcpopen 80,3,10
}
target    2 {
          ipaddr 172.16.1.101 
          tcpopen 80,2,10
}
register  targets 1,2
enable    targets 1,2
//        end of configuration

What should be working:

• You should be able to ping the default gateway (router) 172.16.1.254 from the targets.
• You should be able to ping the virtual web server 172.16.1.10 from the router.
• Clients from the Internet are able to initiate TCP connection to port 80 on the virtual Web Server 172.16.1.10 (now being represented by BalanceNG).
• The targets should be reachable as before, except port 80 which is masked out by and handled by BalanceNG.
• "show servers" and "show targets" in BalanceNG interactive mode should show everything up and operating.

Please contact us in case of further questions, errors or suggestions at info@inlab.de.