H3C Technologies H3C SecBlade LB Cards - Manual (Page 8)

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NAT-mode Layer 4 server load balancing
Figure 1 Network diagram
NAT-mode Layer 4 server load balancing comprises the following elements:
• Cluster—A cluster that provides specific services, including an LB product and multiple servers.
• LB product—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 product to distribute service requests.
Figure 2 Work flow of NAT-mode Layer 4 server load balancing
NAT-mode Layer 4 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.
Server
(1) Request
Dst=VSIP Src=Host IP
LB product Host
(3) DNAT & Distribute request
Dst=Server IP Src=Host IP
(4) Response
Dst=Host IP Src=Server IP
(2) Scheduler
(5) Forward response
Dst=Host IP Src=VSIP
Note:
Dst=Destination IP
Src=Source IP