Stateful Line Module Switchover States

The line module progresses through various high availability states. These states are illustrated in Figure 1.

Figure 1: Stateful Line Module Switchover States

Disabled State

The initial, default state for high availability mode is disabled. While in this state, the router continues to use redundancy mode. If a switchover occurs while the router is in this state, the standby line module performs a cold switchover.

The router enters this state when you power up the router or when the router warm-restarts from a stateful line module switchover. After you enable high availability, the system must meet the following criteria before it can enter the initializing state:

• High availability mode is configured.
• Active line module hardware supports high availability.
• Running configuration allows high availability to operate (that is, no unsupported applications are configured).
• Standby line module hardware supports high availability.
• Standby line module is online and capable of mirroring.
• Standby line module is running the same release as the active line module.

During the disabled state:

• If any one criterion is not met, the system remains in the disabled state, until the criterion is met.
• If a switchover occurs while the system is in the disabled state, the system undergoes a cold-switchover.

The behavior of the router depends on which HA state the application is in when it shifts to a disabled state:

• From initializing state—The router completes the initializing state and transitions to the active state after initialization is complete.
• Active State—The router transitions to the disabled state.

Note: You can use the show redundancy line-card command to display the name of any unsupported applications that are configured.

While in the disabled state, the system operates as if it were configured for redundancy functionality.

If all criteria are met, high availability mode transitions to the initialization state.

Initializing State

After the line module transitions into the initializing state, bulk synchronization of the memory occurs. This activity consists of mirroring of appropriate state and dynamic configuration information from the active line module (memory) to the standby line module (memory). Depending on the size of the configuration, this process can take several minutes.

During the initializing state:

• If an unsupported application is configured during initialization, the system completes initializing and enters the disabled state.
• If any other criterion becomes false (or is no longer met), the system enters the disabled state.
• If a switchover occurs while the system is in this state, the system undergoes a cold-switchover.
• After initialization is completed, the system enters the active state.

Active State

During the active state, the data that was synchronized from the active line module to the standby line module during initialization remains synchronized through mirroring updates.

Mirroring updates occur as follows:

1. When making changes or updates, applications create individual transactions, perform the updates on the active line module, and post the transactions.
2. Following the updates, the active line module sends the changes to the standby line module.
3. The standby line module replays the updates (in the order in which they were committed on the active line module) and makes the appropriate changes for each changed application.

During the active state:

• If a switchover occurs while the router is in the active state, the standby line module performs a warm switchover (that is, stateful line module switchover is in effect).
• If an unsupported application is configured, the system transitions to the disabled state.
• If any other criterion changes (is no longer met), the system transitions to the disabled state.