Cisco FirePOWER ASA 5500 series Configuration Manual page 209

Chapter 14 Configuring Failover
Device Initialization and Configuration Synchronization
Configuration synchronization occurs when one or both devices in the failover pair boot. Configurations
are always synchronized from the active unit to the standby unit. When the standby unit completes its
initial startup, it clears its running configuration (except for the failover commands needed to
communicate with the active unit), and the active unit sends its entire configuration to the standby unit.
The active unit is determined by the following:
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•
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Note If the secondary unit boots without detecting the primary unit, it becomes the active unit. It uses its own
MAC addresses for the active IP addresses. However, when the primary unit becomes available, the
secondary unit changes the MAC addresses to those of the primary unit, which can cause an interruption
in your network traffic. To avoid this, configure the failover pair with virtual MAC addresses. See the
"Configuring Virtual MAC Addresses" section on page 14-25
When the replication starts, the security appliance console on the active unit displays the message
"Beginning configuration replication: Sending to mate," and when it is complete, the security appliance
displays the message "End Configuration Replication to mate." During replication, commands entered
on the active unit may not replicate properly to the standby unit, and commands entered on the standby
unit may be overwritten by the configuration being replicated from the active unit. Avoid entering
commands on either unit in the failover pair during the configuration replication process. Depending
upon the size of the configuration, replication can take from a few seconds to several minutes.
On the standby unit, the configuration exists only in running memory. To save the configuration to Flash
memory after synchronization:
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Startup configurations saved on external servers are accessible from either unit over the network and do
Note
not need to be saved separately for each unit. Alternatively, you can copy the contexts on disk from the
active unit to an external server, and then copy them to disk on the standby unit, where they become
available when the unit reloads.
Command Replication
Command replication always flows from the active unit to the standby unit. As commands are entered
on the active unit, they are sent across the failover link to the standby unit. You do not have to save the
active configuration to Flash memory to replicate the commands.
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If a unit boots and detects a peer already running as active, it becomes the standby unit.
If a unit boots and does not detect a peer, it becomes the active unit.
If both units boot simultaneously, then the primary unit becomes the active unit and the secondary
unit becomes the standby unit.
For single context mode, enter the write memory command on the active unit. The command is
replicated to the standby unit, which proceeds to write its configuration to Flash memory.
For multiple context mode, enter the write memory all command on the active unit from the system
execution space. The command is replicated to the standby unit, which proceeds to write its
configuration to Flash memory. Using the all keyword with this command causes the system and all
context configurations to be saved.
for more information.
Cisco Security Appliance Command Line Configuration Guide
Understanding Failover
14-7