ISSU methods
ISSU supports the following upgrade types:
Compatible upgrade—The running software version is compatible with the upgrade software version. This upgrade type supports the ISSU methods in Table 12.
Incompatible upgrade—The running software version is incompatible with the upgrade software version. The two versions cannot run concurrently.
This upgrade type supports only one upgrade method (also called incompatible upgrade). This method requires a cold reboot. It is service disruptive if hardware redundancy is not available.
Table 12: ISSU methods for compatible upgrade
ISSU method | Description | ||||||||
---|---|---|---|---|---|---|---|---|---|
Incremental upgrade:
| Upgrades only segments that contain differences between the new and old software versions.
| ||||||||
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 |
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. |