H3C Technologies H3C SecPath F1000-E - Manual (Page 867)

2
Working Mechanism of Server Load Balancing
Server load balancing is implemented based on streams. It distributes packets per stream, that is, 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. Server load balancing 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 1 Network diagram for NAT-mode Layer 4 server load balancing
NAT-mode server load balancing includes the following basic 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.
The work flow of NAT-mode server load balancing is as shown in Figure 2 .