HP VPN Firewall Appliances High Availability Configuration Guide

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Working mechanism of server load balancing
Server load balancing is implemented based on streams. It distributes packets in the same stream to the
same server. Server load balancing cannot distribute HTTP-based Layer 7 services based on contents,
restricting the application scope of load balancing services. It can be classified into Network Address
Translation (NAT)-mode server load balancing and direct routing (DR)-mode server load balancing.
NAT-mode server load balancing
Figure 84 Network diagram
NAT-mode server load balancing comprises the following elements:
• Cluster—A cluster that provides specific services, including an LB device and multiple servers.
• LB device—A device that distributes different service requests to multiple servers.
• Server—A server that responds to and processes different service requests.
• VSIP—Virtual Service IP address of the cluster, used for users to request services.
• Server IP—IP address of a server, used for an LB device to distribute service requests.
Host
IP network
LB device
Server A
IP A
Server B
IP B
Server C
IP C
Cluster
VSIP