HP VPN Firewall Appliances High Availability Configuration Guide

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Figure 85 Work flow of NAT-mode server load balancing
NAT-mode server load balancing operates in the following way:
1. The host sends a request, using the host IP as the source IP and VSIP as the destination IP.
2. Upon receiving the request, the LB device uses an algorithm to calculate to which server it
distributes the request.
3. The LB device uses the Destination NAT (DNAT) technology to distribute the request, using the host
IP as the source IP and Server IP as the destination IP.
4. The server receives and processes the request and then sends a response, using the server IP as the
source IP, and the host IP as the destination IP.
5. The LB device receives the response, translates the source IP, and forwards the response, using
VSIP as the source IP, and the host IP as the destination IP.
The work flow shows that NAT is used in server load balancing, and NAT-mode server load balancing
is thus called.