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11-5

Device Manager Guide, Cisco ACE 4700 Series Application Control Engine Appliance

OL-26645-02

Chapter 11 Configuring High Availability

Understanding ACE Redundancy

Fault-Tolerant VLAN

Redundancy uses a dedicated fault-tolerant VLAN between redundant ACEs to transmit flow-state

information and the redundancy heartbeat. Do not use this dedicated VLAN for normal network traffic.

You must configure this same VLAN on both peer ACEs. You also must configure a different IP address

within the same subnet on each ACE for the fault-tolerant VLAN.

The two redundant ACEs constantly communicate over the fault-tolerant VLAN to determine the

operating status of each ACE. The standby member uses the heartbeat packet to monitor the health of

the active member. The active member uses the heartbeat packet to monitor the health of the standby

member. Communications over the switchover link include the following data:

• Redundancy protocol packets

• State information replication data

• Configuration synchronization information

• Heartbeat packets

For multiple contexts, the fault-tolerant VLAN resides in the system configuration data. Each

fault-tolerant VLAN on the ACE has one unique MAC address associated with it. The ACE uses these

device MAC addresses as the source or destination MACs for sending or receiving redundancy protocol

state and configuration replication packets.

Note The IP address and the MAC address of the fault-tolerant VLAN do not change at switchover.

Configuration Synchronization

For redundancy to function properly, both members of an fault-tolerant group must have identical

configurations. Ensure that both ACE appliances include the same bandwidth software license (2G or

1G) and the same virtual context software license. If there is a mismatch in software license between the

two ACE appliances in an FT group, the following operational behavior can occur:

• If there is a mismatch in virtual context software license, synchronization between the active ACE

and standby ACE may not work properly.

• If both the active and the standby ACE appliances have the same virtual content software license

but have a different bandwidth software license, synchronization will work properly but the standby

ACE may experience a potential loss of traffic on switchover from the 2G ACE appliance to the 1G

ACE appliance.

See the Administration Guide, Cisco ACE Application Control Engine for details about the available

ACE software licenses.

The ACE automatically replicates the active configuration on the standby member using a process called

configuration synchronization (config sync). Config sync automatically replicates any changes made to

the configuration of the active member to the standby member. After the ACE synchronizes the

redundancy configuration from the active member to the standby peer, it disables configuration mode on

the standby. See Synchronizing High Availability Configurations with ACE Appliance Device Manager,

page 11-6.

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