Installation guide

1.8 .3.2 . Direct Ro ut ing

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.

Fig u re 1.20. LVS Implemen t ed wit h Direct Ro u t in g

In a typical direct-routing LVS configuration, an LVS router receives incoming server requests

through a virtual IP (VIP) and uses a scheduling algorithm to route the request to real servers. Each

real server processes requests and sends responses directly to clients, bypassing the LVS routers.

Direct routing allows for scalability in that real servers can be added without the added burden on

the LVS router to route outgoing packets from the real server to the client, which can become a

bottleneck under heavy network load.

While there are many advantages to using direct routing in LVS, there are limitations. The most

common issue with direct routing and LVS is with Address Resolution Protocol (ARP).

In typical situations, a client on the Internet sends a request to an IP address. Network routers

typically send requests to their destination by relating IP addresses to a machine's MAC address with

ARP. ARP requests are broadcast to all connected machines on a network, and the machine with the

⁠Chapt er 1 . Red Hat Clust er Suit e Overview