Specifications

Setting Up a Failover Configuration
Equalizer Installation and Administration Guide 47
Setting Up a Failover Configuration
You can set up two Equalizers in a hot backup, or failover, configuration. In such a configuration,
one of the systems handles incoming requests (the primary system), while the other (the backup
system) waits for a failure to occur and automatically takes over if the Equalizer that is currently
handling requests fails. The two Equalizers are called failover peers or siblings in such a
configuration.
To use a second Equalizer as a hot backup or failover peer, you need to install both Equalizers so
their network interfaces have corresponding configurations (see Figure 9 on page 13):
• You must plug the external interface of the backup unit into the same hub or switch into
which the external interface of the primary unit is plugged.
• You must plug the server (or internal) interface of the backup unit into the same hub or switch
into which the server interface of the primary unit is plugged.
• For failover configuration between two switch models, connect a cable from one Equalizer’s
switch interface to the others (see Figure 10 on page 14).
You must designate one of the Equalizers as the preferred primary; the second is the preferred
backup. When you boot both Equalizers at the same time, the preferred primary Equalizer is
activated. If the primary Equalizer fails, the backup takes over. When you bring the failed unit back
online, it assumes the backup role until another failure occurs or you reboot its peer.
A failover configuration requires one or two additional IP addresses, called the failover aliases. In a
dual network configuration, failover aliases must be supplied for both the internal and external
interfaces; in a single network configuration, only an internal alias is needed. These IP addresses are
initially assumed by the preferred primary system and are used as the network-visible interfaces of
the Equalizer, instead of the addresses assigned to the individual Equalizers via the eqadmin
interface. When a failover occurs, the failover aliases are then assumed by the backup system.
When Equalizer is brought online, it checks to make sure that the configured network interfaces are
link active. In the case of the internal interface, Equalizer attempts to ping a configured server or
failover peer. If the interfaces are not active, Equalizer sits in a loop waiting for them to become
active (and sends comments to the console). Once the network interfaces are active, the failover
peers begin a negotiation in which one system becomes the primary unit and the other becomes the
backup unit. This is accomplished by the backup system performing a reboot.
When a backup Equalizer loses contact with its failover peer, it tries to determine the cause. If it
cannot identify the cause, it will try to assume the primary role. It checks that no other system has
configured the gateway IP address or virtual cluster addresses. If these tests are successful, the
Equalizer assumes those IP addresses and starts handling traffic.
A partition occurs when both systems are unable to communicate with each other and both
Equalizers enter primary mode. When the partition is healed and both units regain communication,
the two systems resolve this dispute by choosing one system to reboot itself. Generally, this means
Note – Be sure that you do not create a loop between the external and internal interfaces.