Direct Routing - Red Hat Enterprise Linux 5 Cluster Suite Overview

Chapter 1. Red Hat Cluster Suite Overview
Figure 1.19. LVS Implemented with NAT Routing
In the example, there are two NICs in the active LVS router. The NIC for the Internet has a real IP
address on eth0 and has a floating IP address aliased to eth0:1. The NIC for the private network
interface has a real IP address on eth1 and has a floating IP address aliased to eth1:1. In the event of
failover, the virtual interface facing the Internet and the private facing virtual 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.

1.8.3.2. 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
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