Supervisor High Availability Feature

disabling port channels (PagP), and turning trunking off for ports to which workstations are directly attached, the fast switchover time can be reduced to approximately 10 seconds. In a live network environment, these switchover times present a major disruption to network operations.

The High Availability software feature of Cisco Catalyst OS further enhances the Cisco Catalyst 6500 Series hardware redundancy by also providing protocol redundancy. This feature includes stateful protocol redundancy and image versioning. The High Availability feature must be enabled via the CLI for these features to operate.

Sup-A> (enable) set system highavailability enable

System high availability enabled.

As a general practice with redundant supervisors, it is recommended that the High Availability feature be enabled for normal operation.

Supervisor Stateful Protocol Redundancy

The stateful supervisor switchover is when the switchover time from the active to the standby supervisor is reduced to less than three seconds. This reduced downtime is achieved by synchronizing many of the Layer 2, Layer 3, and Layer 4 protocols1 between the active and standby supervisor engines and is called maintaining protocol state.

For stateful protocol redundancy between dual supervisor engines, a protocol state database is maintained on each supervisor engine for all protocols and features requiring high-availability support. Most of these protocols are only running on the active supervisor engine. In the event of a high-availability switchover, the new active supervisor engine can start the protocols from the updated database state, rather than the initialization state. This is how a redundant system can maintain stateful protocol redundancy and minimal network downtime when the active supervisor engine goes ofﬂine.

•High Availability Supported Feature— High availability if fully supported. The state of the feature is preserved between the active and standby supervisor engines in the protocol database.

•High Availability Compatible Feature— High availability is not supported for these features. The protocol database for these features is not synchronized between supervisor engines. The feature can be used if the High Availability feature is enabled. For example, if GARP Multicast Registration Protocol (GMRP) and high availability were both enabled and a high-availability supervisor engine failover took place, the GMRP protocol would be restarted from the initialization state (non-stateful). The stateful protocol redundancy is still in place for the supported features if a compatible feature is enabled.

•High Availability Incompatible Feature— High availability is not supported. The protocol database for these features is not synchronized between supervisor engines. The feature should not be enabled if the High Availability feature is enabled. These features are not supported with high availability enabled because incorrect behavior may result.

Important: Do not use these features if a high-availability system is required.

1. Layer 4 protocols include the Layer 4 information in extended IP access lists.

Cisco Systems, Inc.

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