Cisco 7604 Configuration Manual page 264

Understanding Failover
The active unit is determined by the following:
If a unit boots and detects a peer already running as active, it becomes the standby unit.
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If a unit boots and does not detect a peer, it becomes the active unit.
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If both units boot simultaneously, then the primary unit becomes the active unit and the secondary
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unit becomes the standby unit.
If the secondary unit boots without detecting the primary unit, it becomes the active unit. It uses its own
Note
MAC address for the active IP addresses. However, when the primary unit becomes available, the
secondary unit changes the MAC address to that of the primary unit, which can cause an interruption in
your network traffic.
When the configuration synchronization starts, the FWSM console on the active unit displays the
message "Beginning configuration replication: Sending to mate," and when it is complete, the FWSM
console displays the message "End Configuration Replication to mate." During the configuration
synchronization, 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.
If you enter the write standby command on the active unit, the standby unit clears its running
configuration (except for the failover commands used to communicate with the active unit), and the
active unit sends its entire configuration to the standby unit.
In multiple context mode, when you enter the write standby command in the system execution space,
all contexts are replicated. If you enter the write standby command within a context, the command
replicates only the context configuration.
On the standby unit, the replicated configuration exists only in running memory. To save the
configuration to Flash memory after synchronization:
In single context mode, enter the write memory command on the active unit. The command is
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replicated to the standby unit, which proceeds to write its configuration to Flash memory.
In multiple context mode, enter the write memory all command on the active unit from the system
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execution space. This command saves the system configuration and all context configurations. The
command is replicated to the standby unit, which proceeds to write its configurations to Flash
memory. Contexts with startup configurations on external servers are accessible from either unit
over the network and do 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.
Note If you previously changed the number or size of memory partitions on the primary unit (see the
"Managing Memory for Rules" section on page
configuration, immediately reload the secondary unit so that the memory partitions are the same. During
the initial synchronization, the configuration might not fit properly in the secondary unit memory
partitions, but after reloading, and another configuration synchronization, the secondary unit will be
operational.
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM
14-10
4-11), then after the secondary unit synchronizes the
Chapter 14 Configuring Failover
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