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# Understanding SRP State Behavior

The SRP progresses through various high availability states. These states are illustrated in Figure 27.

Figure 27: 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.

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

- High availability mode is configured.
- Active SRP hardware supports high availability.
- Network core dump feature is disabled.
- Running configuration will allow high availability to operate (that is, no unsupported applications are configured).
- Standby SRP hardware supports high availability.
- Standby SRP module is online and capable of mirroring.
- Standby SRP module is running the same release.

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 cold-restarts.

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:

- File synchronization of the primary NVS with the standby NVS
- Mirroring of appropriate state and dynamic configuration information from the active SRP (memory) to the standby SRP (memory)

  | Note: 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 pending 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 cold-restarts.

Once 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:

- If a switchover occurs while the router is in the active state, the standby SRP module performs a warm restart (that is, stateful SRP switchover is in effect); the standby SRP module uses the configuration located in NVS.
- If an unsupported application is configured, the system transitions to the pending state.
- If any other criterion changes (is no longer met), the system transitions to the disabled state.

  | Note: Changes made in manual commit mode are maintained, uncommitted, in the standby SRP memory until a trigger to commit occurs; if a switchover occurs while in this mode, the standby SRP module uses the configuration in memory.

## 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:

- From disabled state—The router remains in the disabled state.
- From initializing state—The router completes the initializing state and transitions to the pending state after initialization is complete.
- Active State—The router transitions to the 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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