Allot NetEnforcer AC-1000 Series, Hardware Manual

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Chapter 4: Redundancy
NetEnforcer AC-1000 Hardware Guide 4-13
Parallel Redundancy
Failure of a network device can be catastrophic, causing network downtime and lost
business. The key to designing any mission-critical network is to recognize that these
failures can occur, and to design a network that can handle failures and still allow the
network to function. In order to do this, it is important to use the most reliable
equipment, with redundancy built in to all mission-critical equipment.
A NetEnforcer can operate in parallel to provide Parallel Redundancy. Parallel
Redundancy requires two NetEnforcer systems and, where an external Bypass Unit is
used, a single Bypass Unit.
The Primary NetEnforcer handles the traffic and the Secondary NetEnforcer is designed
to stand by as long as the Primary NetEnforcer is active. Only if, for any reason, the
Primary NetEnforcer is not able to function properly does the Secondary NetEnforcer
become active.
Both NetEnforcers receive traffic from the internal network, but only the Primary
NetEnforcer is passing the traffic to the external network.
While the Primary NetEnforcer receives and handles traffic coming from the external
network, the Secondary External interface is disabled, since the system is in Standby
mode. If the Primary NetEnforcer should fail, the Secondary NetEnforcer automatically
takes control of the traffic, and enables its External interface.
In Parallel Redundancy mode, Bypass mode is activated in the unlikely event that both
the Primary and Secondary NetEnforcers fail.