Red Hat ENTERPRISE LINUX 4 Manual

Also see for ENTERPRISE LINUX 4 - DEVELOPER TOOLS GUIDE: Installation guide Installation guide Tuning guide Installation guide Manual

Contents

Routing Methods31Figure 1.23. LVS Implemented with NAT RoutingIn the example, there are two NICs in the active LVS router. The NIC for the Internet has a real IPaddress on eth0 and has a floating IP address aliased to eth0:1. The NIC for the private networkinterface has a real IP address on eth1 and has a floating IP address aliased to eth1:1. In the event offailover, the virtual interface facing the Internet and the private facing virtual interface are taken overby the backup LVS router simultaneously. All the real servers on the private network use the floatingIP for the NAT router as their default route to communicate with the active LVS router so that theirabilities 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 addressare aliased to two physical NICs. While it is possible to associate each floating IP address to itsphysical 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 routeruses network address translation to replace the address of the real server in the packets with the LVSrouters public VIP address. This process is called IP masquerading because the actual IP addressesof 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 largedeployments because it must process outgoing and incoming requests.1.8.3.2. Direct RoutingDirect routing provides increased performance benefits compared to NAT routing. Direct routingallows the real servers to process and route packets directly to a requesting user rather than passing