Direct Routing - Red Hat ENTERPRISE LINUX 4 - VIRTUAL SERVER ADMINISTRATION Manual

Chapter 1. Linux Virtual Server Overview
Using this NAT routing, the real servers may be any kind of machine running various operating
systems. The main disadvantage is that the LVS router may become a bottleneck in large cluster
deployments because it must process outgoing as well as incoming requests.

1.4.2. Direct Routing

Building an LVS setup that uses direct routing provides increased performance benefits compared to
other LVS networking topologies. Direct routing allows the real servers to process and route packets
directly to a requesting user rather than passing all 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.
Figure 1.4. LVS Implemented with Direct Routing
In the typical direct routing LVS setup, the LVS router receives incoming server requests through
the virtual IP (VIP) and uses a scheduling algorithm to route the request to the real servers. The
real server processes the request and sends the response directly to the client, bypassing the LVS
routers. This method of 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.
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