4.1.2. Routing on the Real Servers
The most important thing to remember when configuring the real servers network interfaces in a NAT cluster is to set the gateway for the NAT floating IP address of the LVS router. In this example, that address will be 10.11.12.10.
Once the network interfaces are up on the real servers, the machines will be unable to ping or connect in other ways to the public network. This is normal. You will, however, be able to ping the real IP for the LVS router's private interface, in this case 10.11.12.8.
So the real server's /etc/sysconfig/network-scripts/ifcfg-eth0 file could look similar to this:
DEVICE=eth0 ONBOOT=yes BOOTPROTO=static IPADDR=10.11.12.1 NETMASK=255.255.255.0 GATEWAY=10.11.12.10
If a real server has more than one network interface configured with a GATEWAY= line, the first one to come up will get the gateway. Therefore if both eth0 and eth1 are configured and eth1 is used for LVS clustering, the real servers may not route requests properly.
It is best to turn off extraneous network interfaces by setting ONBOOT=no in their network scripts within the /etc/sysconfig/network-scripts/ directory or by making sure the gateway is correctly set in the interface which comes up first.