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Both supervisor engines run a synchronizing operation to allow for transfer of this data. When a database entry is updated on
the active supervisor engine, the synchronizing operation places the update in a first-in, first-out (FIFO) queue. This queue is
scheduled to empty periodically for transfer to the standby supervisor. The transfer is a background process and as such, the
update interval varies depending on the number of other active processes in the system. The update interval ranges from one
to five seconds with two seconds being an approximate average. The standby supervisor engine's synchronizing process
receives these asynchronous updates and enters them into the protocol state database on the standby supervisor engine. When
the system starts or when a second supervisor engine is hot-inserted, a global synchronization takes place between the protocol
databases to ensure all protocol states are up to date.
Figure 2
Stateful Protocol Database Depiction
To summarize the stateful protocol feature, the high-availability switchover performance is more dependent on the status of
the synchronization procedure than on the complexity of the configuration. After the system and protocols reach a stable
operating point, the protocol state databases on each of the supervisor engines will have a fairly similar status (depending on
updates in the queue). The determining factor for switchover performance is the number of updates in the queue that have not
been completed. The resulting high-availability supervisor engine switchover performance is less than three seconds.
Supervisor Engine Software Image Upgrades
In a redundant supervisor engine configuration, Cisco Catalyst OS images must be properly managed to ensure high
availability of the system. The following section describes some options for managing Cisco Catalyst OS images.
Supervisor Engine Image Synchronization
By default on the Cisco Catalyst 6500 Series, the Cisco Catalyst OS software images on the active and the standby supervisor
engines must be the same. This allows the system to maintain a stable operating environment by ensuring that the supervisor
engine switchover occurs with the same software features and revisions on the new active supervisor engine as on the
previously active supervisor engine. If the two images are not the same version during system bootup, the active supervisor
engine downloads its current boot image to the standby supervisor engine. The NVRAM configuration of the active supervisor
engine is also synchronized between the supervisor engines.
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