An example of a two-armed LoadMaster site may look as follows.

The system has been configured as follows:

  • A Virtual Service has been created on the LoadMaster with an IP address of 192.168.0.110 for an HTTP service.

  • The Virtual Service has been configured to balance the incoming traffic across the Real Servers (server 1, 2 and 3).

  • A user requests the URL http://www.kemptechnologies.com.

  • The URL will be resolved by the DNS into IP address 66.220.13.66.

  • The request will be routed to the firewall, which will NAT to the Virtual Service address (192.168.0.110) on eth0 (192.168.0.100/24).

  • The LoadMaster is connected to the server farm subnet 10.0.0.0/24 using its network interface eth1 (10.0.0.10/24).

  • The LoadMaster knows that there are three Real Servers in this subnet that are assigned to the requested address 192.168.0.110 and are able to deliver the required content.

  • The LoadMaster uses the load balancing method configured, for example weighted round robin, to send the request on to one of the three Real Servers.

  • Other items to note regarding the two-armed configuration are:

  • Both eth0 (net side) and eth1 (farm side) interfaces are used. Additional ports go to the farm side for multi-armed configurations
  • Implies that the LoadMaster (eth0) and server farm(s) are on separate logical networks, sometimes referred to as a NAT-based topology
  • The server farm(s) may make use of non-routable (RFC1918) IP addresses
  • Server NAT may be useful in such a configuration
  • IP address transparency will function properly if clients are located on the same logical network as the LoadMaster in both NAT (common) and DSR (uncommon) configurations.
  • Virtual Services may be created on any interface/VLAN that has an IP address configured.

Leveraging one port and configuring the “Additional Subnet” feature qualifies as two-armed.