Cisco Cisco IOS Software Release 12.4(22)XR

If you enable high availability when the standby supervisor engine is running, image version 
compatibility is checked and if found compatible, the database synchronization starts. High availability 
compatible features continue from the saved states on the standby supervisor engine after a switchover.

When you disable high availability, the database synchronization is not done and all features must restart 
on the standby supervisor engine after a switchover.

If you change high availability from enabled to disabled, synchronization from the active supervisor 
engine is stopped and the standby supervisor engine discards all current synchronization data.

If you change high availability from disabled to enabled, synchronization from the active to standby 
supervisor engine is started (provided the standby supervisor engine is present and its image version is 
compatible). 

NVRAM synchronization occurs irrespective of high availability being enabled or disabled (provided 
there are compatible NVRAM versions on the two supervisor engines). 

If you do not install a standby supervisor engine during system bootup, the active supervisor engine 
detects this and the database updates are not queued for synchronization. Similarly, when you reset or 
remove the standby supervisor engine, the synchronization updates are not queued and any pending 
updates in the synchronization queue are discarded. When you hot insert or restart a second supervisor 
engine that becomes the standby supervisor engine, the active supervisor engine downloads the entire 
system database to the standby supervisor engine. Only after this global synchronization is completed, 
the active supervisor engine queues and synchronizes the individual updates to the standby supervisor 
engine.

When you hot insert or restart a second supervisor engine, it might take a few minutes for the global 
synchronization to complete. 

For more information about High Availability, including configuration details, and information about 
power management, refer to the 

 section, as well as the documents 

at the following urls:

Catalyst 6500 Series Software Configuration Guide (6.1.1a), with special attention to the 
“Configuring Redundancy” chapter at:

Catalyst 6000 Family IOS Software Configuration Guide, Release 12.2(9)YO at:

MIP

PPP (Point-to-Point Protocol)

AAA (Authentication, Authorization, and Accounting)

VPDN (Virtual Private Data Network) using L2TP

RADIUS (Remote Authentication Dial-In User Service)