Stateful SRP Switchover States

The SRP progresses through various high availability states. These states are illustrated in Figure 4.

Figure 4: High Availability States

High Availability States

Disabled State

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

The router enters this state when you power up the router or when the router warm-restarts from an SRP switchover.

After you enable high availability, the system must meet the following criteria before it can enter the initializing state:

During the disabled state:

While in the disabled state, the system operates as if it were configured for file system synchronization (for example, NVS is synchronized every 5 minutes, if autosynchronization is enabled).

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

Initializing State

After the SRP module transitions into the initializing state, bulk synchronization of the memory and NVS occurs. This includes the following:

During the initializing state:

After initialization is completed, the system enters the active state.

Active State

During the active state, the data that was synchronized from the active SRP module to the standby SRP 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 SRP module, and post the transactions.
  2. Following the updates, the active SRP module sends the changes to the standby SRP module.
  3. The standby SRP module replays the updates (in the order in which they were committed on the active SRP module) and makes the appropriate changes for each changed application.
  4. Updates that need to be stored in NVS (that is, for static configurations) are updated in NVS.

    Note: While in the active and pending states, the CLI synchronize command does not update configuration files; these files are updated by the mirroring process.

During the active state:

Pending State

The system transitions to the pending state if an unsupported application is configured. When a transition to the pending state occurs, the system generates SNMP traps and log messages.

How the router behaves depends on which HA state the application is in when it shifts to a pending state:

The system remains in the pending state until the configuration of the unsupported application is removed. However, even though it is in the pending state, the system continues mirroring updates from the primary SRP module to the standby SRP module.

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

If a switchover occurs while the system is in the pending state, the system cold-restarts.

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