# Guidelines for Upgrading Software

You cannot activate stateful SRP switchover when a different release of software is running on the standby SRP module. The router determines whether a release is the same by viewing the build date, the release filename, and the internal version number for the software on each SRP module.

The most efficient way to upgrade the software is to ensure that the standby SRP module is armed with the new release and then reload the standby SRP module. This reload occurs automatically after you download and arm a new release onto the active SRP module and the active SRP module subsequently synchronizes with the standby SRP module.

After reloading, and even though high availability mode is configured, the active SRP module reverts to using the file-system-synchronization operational mode for synchronizing updates. To complete the upgrade and place the system back in high-availability operational mode, you must execute the srp switch command to force the standby SRP module to take over as the active SRP module.

| Note: Executing the srp switch command results in a cold restart of the router.

After the switchover is initiated, the formerly active SRP module reloads the software and starts running the same release as the newly active SRP module. When the formerly active SRP module becomes operational as the standby SRP module, the newly active SRP module detects that the release it is running is the same as that on the standby SRP module and allows the originally active SRP module to resume the high-availability operational mode.

If a fault occurs when the active SRP module is in file-system-synchronization operational mode, the standby SRP module detects the fault and takes over, and the router cold-restarts. For this reason, you must arm the new release only when you can accept the resulting window of vulnerability where high availability is disabled (that is, until the active and standby SRP modules are again running the same release).

#### Related Documentation

- Stateful SRP Switchover Redundancy Modes
- Stateful SRP Switchover States
- srp switch