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Performing an ISSU
Overview
The In-Service Software Upgrade (ISSU) feature upgrades software with a minimum amount of
downtime.
ISSU is implemented on the basis of the following design advantages:
Separation of service features from basic functions—Device software is segmented into
boot, system, and feature images. The images can be upgraded individually.
Independence between service features—Features run independently. One feature can be
added or upgraded without affecting the operation of the system or other features.
Support for hotfix—Patch images are available to fix system bugs without a system reboot.
Hardware redundancy—In an IRF fabric, one member device can be upgraded while other
member devices are providing services.
For more information about images, see "Upgrading software."
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
1.
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.
1. ISSU methods for compatible upgrade
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.
Reboot
CAUTION:
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.
ISSU commands
ISSU provides the install and issu command sets. After you identify the ISSU method, use 1 to
choose the command set you want to use.
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