# Unified ISSU Initialization Phase Overview

When you issue the issu initialize command, unified ISSU first verifies whether all requirements for the upgrade are met. The verification process examines the running release, the SRP modules, the line modules, line module redundancy, and the router configuration.

The issu initialize command does not interrupt or disrupt any of the runtime operations of the router. The command has no effect on changes of authorization, forwarding, or subscribers (except perhaps, rate of logins). You cannot manually change the file system redundancy mode from high availability to file synchronization until the unified in-service software upgrade is completed.

| Note: We recommend that you make no configuration changes after you have issued the issu initialization command. As a best practice, ensure that your configuration is complete before you start the software upgrade.

During the initialization phase, you can halt the unified in-service software upgrade at any time and revert either to a normal SRP module switchover or to the previous state of the router. To stop the unified ISSU process, you must issue the issu stop command. If instead you simply exit the CLI session, the unified ISSU initialization phase continues.

The action taken when a requirement is not met depends on the requirement. For some failed verifications, the CLI warns you of the issue and prompts you to proceed or quit the upgrade process. More serious failures cause the CLI to exit the command and provide a message describing the issue.

| Note: We recommend that you issue the show issu command before beginning the unified in-service software upgrade. The output of the command lists any necessary conditions that are not currently met on the router. You can therefore correct these failures before entering into the upgrade. You can issue the show issu command at any time.

| Note: On E120 and E320 routers, you can hot swap an IOA during the initialization phase without affecting the in-service software upgrade. However, we strongly recommend that you perform any necessary hot swaps before you issue the issu initialize command.

If the standby SRP module reloads during the initialization phase, unified ISSU is halted. You must begin again by issuing the issu initialize command.

## Application Data Upgrade on the Standby SRP Module

Synchronized modules can become unsynchronized because you can change the router configuration at any time until you issue the issu start command. When the verification process is completed, unified ISSU starts up the stateful SRP switchover process to maintain synchronization between the active SRP module and the standby SRP module during the SRP module upgrade phase.

| Note: An SRP switchover from the active SRP module to the standby SRP module at this point in the unified in-service software upgrade causes a cold restart of the router because the SRP modules are running two different releases. The current release is on the active SRP module and the upgrade release is on the standby SRP module.

The application and configuration data that has been mirrored to the standby SRP module is upgraded as required by the new software release. The CLI displays the progress of the SRP module upgrade.

While data on the standby SRP module is upgraded, any new changes that are mirrored from the primary SRP module to the standby SRP module are also upgraded to the version required by the armed release.

| Note: This process consumes significant CPU resources on the redundant SRP module and can take a considerable amount of time to complete. Performance of the active SRP module might be affected during the SRP module upgrade.

When the upgrade release has been synchronized to the standby SRP module, stateful SRP switchover is disabled until the unified in-service software upgrade is completed.

If you configure an application that does not support unified ISSU during the initialization phase, the initialization phase completes, but the issu start command subsequently fails.

## SNMP Traps

When you issue the issu initialization command, the SNMP agent generates a juniSystemIssuStateChange trap with juniSystemIssuState set to initializing. When the unified ISSU initialization is completed, the SNMP agent generates a juniSystemIssuStateChange trap with juniSystemIssuState set to initialized.

#### Related Topics

- Unified ISSU Phases Overview
- Halt of Unified ISSU During Initialization Phase Overview
- Halting Unified ISSU During Initialization Phase
- issu initialize
- issu start
- issu stop
- show issu