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Chapter 14 Working with Network Services 245
Setting Up IP Failover
IP failover allows a secondary server to acquire the IP address of a primary server if the
primary server ceases to function. Once the primary server returns to normal operation,
the secondary server relinquishes the IP address. This allows your website to remain
available on the network even if the primary server temporarily goes offline.
Note: IP failover only allows a secondary server to acquire a primary server’s IP address.
You need additional software tools, such as rsync, to provide capabilities such as
mirroring the primary server’s data on the secondary server. See the rsync man page
for more information.
IP Failover Prerequisites
IP failover isn’t a complete solution; it is one tool you can use to increase your server’s
availability to your clients. To use IP failover, you need to set up the following hardware
and software.
Hardware Requirements
IP failover requires the following hardware setup:
 Primary server
 Secondary server
 Public network (the servers must be on same subnet)
 Private network between the servers (requires an additional network interface card)
Note: Because IP failover uses broadcast messages, both servers must have IP
addresses on the same subnet of the public network. Both servers must also have IP
addresses on the same subnet of the private network.
Software Requirements
IP failover requires the following software setup:
 Unique IP addresses for each network interface (public and private)
 Software to mirror primary server data to the secondary server
 Scripts to control failover behavior on the secondary server
IP Failover Operation
When IP failover is active, the primary server periodically broadcasts a brief message
confirming normal operation on both the public and private networks. This message is
monitored by the secondary server.
 If the broadcast is interrupted on both public and private networks, the secondary
server initiates the failover process.
 If status messages are interrupted on only one network, the secondary server sends
email notification of a network anomaly, but doesn’t acquire the primary server’s IP
address.