ISSU methods

ISSU supports the following upgrade types:

Table 12: ISSU methods for compatible upgrade

ISSU method

Description

Incremental upgrade:

  • Service Upgrade

  • File Upgrade

Upgrades only segments that contain differences between the new and old software versions.

  • Service upgrade—Upgrades service features. The upgrade does not affect the operation of features that are not being upgraded.

  • File upgrade—Upgrades hidden system program files. The system can provide services during the upgrade.

ISSU Reboot

Reboots CPUs to complete software upgrade. During the reboot, the data plane can still forward traffic.

This method saves all data (running, configuration, and hardware) and status to memory before rebooting CPUs. For services that require regular communication with their peers, this method uses protocol agents to maintain their connectivity and status.

After the reboot, all data is restored to CPU.

Reboot


[CAUTION: ]

CAUTION:

This method reboots both the control and data planes to complete the software upgrade.


The Reboot method is service disruptive if the device stands alone. As a best practice, schedule the downtime carefully to minimize the upgrade impact on the services.

This method reboots both the control and data planes to complete the software upgrade.