Riverstone Networks WICT1-12 - Manual (Page 514)

22-16 Riverstone Networks RS Switch Router User Guide Release 8.0
Load Balancing Web Hosting Configuration
Load Balancing with NAT
In the following example, several services (including DNS) are distributed between two separate servers. Occasionally,
the load balancing server will need to make its own DNS request to the Internet in order to resolve a client’s DNS
request. Network Address Translation (NAT) on the RS allows the load balancing servers to use a “global” IP address
for Internet requests. NAT translates the “local” address of the load balancing server to the global address for the
outgoing request and translates the global address back to the local address for the incoming reply. This process is
illustrated in
Figure 22-6 .
Figure 22-6 Load balancing with NAT
The following explains the data flows shown in Figure 22-6 :
1. The client sends a DNS request to the virtual IP address 135.1.1.1:53.
2. The client’s DNS request is redirected to a load balancing server.
3. The load balancing server sends a request to an authoritative DNS server on the Internet. NAT on
the RS translates the load balancing server’s internal IP address (10.1.1.1) to the global IP address
136.1.1.100 for the request. For the reply, NAT translates the global IP address back to the internal
IP address and sends the reply message to the load balancing server.
4. The load balancing server sends a DNS reply back to the client.


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