Setting Up Lvs; The Nat Lvs Network; Configuring Network Interfaces For Lvs With Nat - Red Hat ENTERPRISE LINUX 5 - VIRTUAL SERVER ADMINISTRATION Manual

Chapter 3.

Setting Up LVS

LVS consists of two basic groups: the LVS routers and the real servers. To prevent a single point of
failure, each groups should contain at least two member systems.
The LVS router group should consist of two identical or very similar systems running Red Hat
Enterprise Linux. One will act as the active LVS router while the other stays in hot standby mode, so
they need to have as close to the same capabilities as possible.
Before choosing and configuring the hardware for the real server group, determine which of the three
LVS topologies to use.

3.1. The NAT LVS Network

The NAT topology allows for great latitude in utilizing existing hardware, but it is limited in its ability to
handle large loads because all packets going into and coming out of the pool pass through the LVS
router.
Network Layout
The topology for LVS using NAT routing is the easiest to configure from a network layout
perspective because only one access point to the public network is needed. The real servers pass
all requests back through the LVS router so they are on their own private network.
Hardware
The NAT topology is the most flexible in regards to hardware because the real servers do not
need to be Linux machines to function correctly. In a NAT topology, each real server only needs
one NIC since it will only be responding to the LVS router. The LVS routers, on the other hand,
need two NICs each to route traffic between the two networks. Because this topology creates a
network bottleneck at the LVS router, gigabit Ethernet NICs can be employed on each LVS router
to increase the bandwidth the LVS routers can handle. If gigabit Ethernet is employed on the LVS
routers, any switch connecting the real servers to the LVS routers must have at least two gigabit
Ethernet ports to handle the load efficiently.
Software
Because the NAT topology requires the use of iptables for some configurations, there can be
a fair amount of software configuration outside of Piranha Configuration Tool. In particular, FTP
services and the use of firewall marks requires extra manual configuration of the LVS routers to
route requests properly.

3.1.1. Configuring Network Interfaces for LVS with NAT

To set up LVS with NAT, you must first configure the network interfaces for the public network and the
private network on the LVS routers. In this example, the LVS routers' public interfaces (eth0) will be
on the 192.168.26/24 network (I know, I know, this is not a routable IP, but let us pretend there is a
firewall in front of the LVS router for good measure) and the private interfaces which link to the real
servers (eth1) will be on the 10.11.12/24 network.
So on the active or primary LVS router node, the public interface's network script, /etc/sysconfig/
network-scripts/ifcfg-eth0, could look something like this:
DEVICE=eth0
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