Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 5.2 Overview page 43

Routing Methods
interface are taken over by the backup LVS router simultaneously. All the real servers on the
private network use the floating IP for the NAT router as their default route to communicate with
the active LVS router so that their abilities to respond to requests from the Internet is not
impaired.
In the example, the LVS router's public LVS floating IP address and private NAT floating IP
address are aliased to two physical NICs. While it is possible to associate each floating IP
address to its physical device on the LVS router nodes, having more than two NICs is not a
requirement.
Using this topology, the active LVS router receives the request and routes it to the appropriate
server. The real server then processes the request and returns the packets to the LVS router.
The LVS router uses network address translation to replace the address of the real server in the
packets with the LVS routers public VIP address. This process is called IP masquerading
because the actual IP addresses of the real servers is hidden from the requesting clients.
Using NAT routing, the real servers can be any kind of computers running a variety operating
systems. The main disadvantage of NAT routing is that the LVS router may become a
bottleneck in large deployments because it must process outgoing and incoming requests.
8.3.2. Direct Routing
Direct routing provides increased performance benefits compared to NAT routing. Direct routing
allows the real servers to process and route packets directly to a requesting user rather than
passing outgoing packets through the LVS router. Direct routing reduces the possibility of
network performance issues by relegating the job of the LVS router to processing incoming
packets only.
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