Extreme Networks Px Series - Manual (Page 72)

6-14 Px Series Application Switch Installation and Configuration Guide
NAT Modes
Network address translation (NAT) is one of the cornerstones of server load balancing.
To balance the load between the various real servers, the server load balancer uses a
single IP address, called a virtual IP address, to represent the entire group of servers
that make up a website.
When a client request arrives at the virtual IP address, the load balancer must rewrite
the destination IP address, so that it can forward the request to a server for processing.
Likewise, when the server responds to the request, the server address must also be
translated from its own unique address to that of the virtual IP, so that it can be sent
back to the user. This process of translating one network address into another is called
network address translation (NAT).
Full-NAT Mode
In full-NAT mode, the server load balancer translates both the source and destination IP
addresses—those of the client and the server—before sending the request onto the user.
For the point of view of the server fulfilling the request, it appears as though the client
making the request is actually the server load balancer.
Advantages of full-NAT mode are:
• No configuration is necessary on the Layer 2/3 switch connected to the application
switch.
• It can be deployed in any network architecture.
• Clients can be on the same subnet as the servers.
• It allows interoperation with any vendors switch, regardless of support for policy
routing.
You must run in full-NAT mode if:
• Clients and servers are on the same layer 2 network segment.
• The switch connected to the application switch does not support layer 3 policy
routing based on source IP address, port, and protocol.
• You do not have access to the layer 3 switch to configure policy based routing.