Specifications
Chapter 1: Overview
14 Equalizer Installation and Administration Guide
Figure 10 shows a sample of the cabling of the Equalizers shown in Figure 9.
Figure 10 Cablingexamplefromthesamplefailoverconfiguration
The backup-unit Equalizer monitors all traffic to and from the primary unit; both Equalizers
periodically exchange status messages over the local area network. The sibling Equalizers also
exchange current configuration information. When you update the configuration on either machine,
the configuration on its sibling is automatically updated.
Should either Equalizer fail to respond to a status message probe, the survivor begins a diagnostic
cycle and attempts to contact its sibling via the other network ports. If these attempts fail, the sibling
is considered to be down.
When the backup Equalizer determines that its sibling is down, it initiates a failover process:
1. The backup Equalizer configures the virtual cluster aliases on the external port and sends out
“gratuitous ARP” packets that instruct any external-network routers to replace ARP table
entries that point to the physical address of the failed Equalizer with the physical address of the
backup unit.
2. The backup Equalizer configures a failover gateway alias on the port that is local to the servers.
n
With no backup configuration, the servers use the IP address of the cluster or external
port as their default gateway.
n
In a hot-backup environment, the gateway address can migrate between the primary and
backup unit. This requires an additional address.
3. The Equalizer kernel changes from BACKUP mode to PRIMARY mode. The PRIMARY-mode
Equalizer performs gateway routing of packets between its cluster and external ports, address
translation, and load balancing.
When a failed unit is brought back online, it begins to exchange status messages with its
sibling. Once both Equalizers have synchronized, the newly-started unit assumes the backup
role.
Using Reserved IP Addresses
In environments in which conserving IP addresses is important, using reserved IP addresses can
minimize the number of “real” IP addresses needed. Equalizer supports placing servers on reserved,
non-routable networks such as the class A network 10.0.0.0 and the class C network 192.168.2.0.
To Switch
(External Interface)
To Servers
(Server Interface)
To Switch
(External Interface)
To Servers
(Server Interface)
For Failover