Hardware Load Balancing Requirements

Using a hardware load balancer comes at a greater cost than DNS load balancing, but adds some flexibility and backward compatibility that an organization might require. Configuring the hardware load balancer is typically the most difficult part of an Edge Server deployment simply because of how flexible the load-balancing software generally is.

Some basic guidelines must be followed when using a hardware load balancer for Edge services:

• Each external-facing Edge service needs a publicly routable virtual IP address.

• Each Edge Server needs three publicly routable IP addresses assigned.

To summarize the requirements, if an organization deploys two Edge Servers with a hardware load balancer, it needs nine publicly routable IP addresses: three for the virtual IP addresses and three for each Edge Server. That logical configuration is depicted in Figure 31.7.

Figure 31.7. Hardware load balancer VIPs and Edge Server real IPs.

In addition to the public IP addressing requirements, there are some stipulations about what type of Network Address Translation must be configured on the load balancer. For traffic from the Internet to the server, the hardware load balancer must use Destination Network Address Translation (DNAT).

This means that as a packet is received from the Internet to the virtual IP address, the hardware load balancer rewrites the packet to change the destination IP address to one of the IP addresses actually assigned to an Edge Server network adapter.

For traffic from the server to the Internet, the load balancer must be configured for Source Network Address Translation (SNAT). This means that packets sent outbound from the Edge Servers are translated by the load balancer back to the virtual IP address that the external Internet clients expect to communicate with.