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8-2

Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex

Chapter 8 Configuring the Cisco IOS XE In Service Software Upgrade Process

Prerequisites to Performing ISSU

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Prerequisites to Performing ISSU

Before performing ISSU, you must meet these prerequisites:

• A permanent “ISSU barrier" exists between pre-IOS XE 3.6.0E and IOS XE 3.6.0 releases: ISSU is

supported between versions on the same side of the barrier but it is not supported between versions

on opposite sides.

Note This restriction applies to Catalyst 4500X in a VSS, as well as to Supervisor Engine 7E,

Supervisor Engine 7LE, and Supervisor Engine 8E in a VSS or in a redundant chassis.

Four scenarios will illustrate the restriction:

If you are running a release prior to IOS XE 3.6.0E (3.5.1E, for example), you cannot perform

an ISSU upgrade to IOS XE 3.6.0E.

If you are running IOS XE 3.6.0E, you cannot perform an ISSU downgrade to IOS XE 3.5.0E.

If you are running IOS XE 3.6.0E, you can perform an ISSU upgrade to IOS XE 3.6.1E (when

released).

If you are running a release after IOS XE 3.6.0E (for example, 3.7.0, when released), you cannot

perform an ISSU downgrade to IOS XE 3.5.0E.

• The type of the existing and target image must match. You cannot upgrade from a Universal Lite

image to a Universal image (and vice versa) without experiencing several minutes of traffic loss. The

same restriction applies between crypto and non-crypto images.

• The active and the standby supervisor engines must have the same supervisor engine hardware (same

model, same memory, and so on).

• The new and old Cisco IOS XE software images must be loaded into the file systems (bootflash, SD

card, or USB) of both the active and the standby supervisor engines before you begin the ISSU

process.

The old software image should be available either in bootflash, SD card, or USB and the system

should have been booted from one of these locations because the boot variable must be changed

before the ISSU process starts.

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