Cisco Catalyst 4500 Series Configuration Guide

6-3
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
OL-25340-01
Chapter 6 Configuring the Cisco IOS XE In Service Software Upgrade Process
About Performing ISSU
• If you enter the no ip routing command, ISSU falls back from SSO to RPR mode, resulting in traffic
loss.
• Autoboot is turned on and the current booted image matches the one specified in the BOOT
environmental variable. For details on how to configure and verify these, please refer to "Modifying
the Boot Field and Using the boot Command, page 3-27.
• If you enter the no ip routing command, ISSU falls back from SSO to RPR mode, resulting in traffic
loss.
About Performing ISSU
Note Do not make any hardware changes while performing ISSU.
Before you perform ISSU, you should understand the following concepts:
• Stateful Switchover, page 6-3
• NSF, page 6-5
• ISSU Process, page 6-6
• Performing an ISSU Upgrade: 2 Methods, page 6-11
• Changeversion Process, page 6-12
• Guidelines for Performing ISSU, page 6-13
• Compatibility Matrix, page 6-13
• SNMP Support for ISSU, page 6-14
• Compatibility Verification Using Cisco Feature Navigator, page 6-14
Stateful Switchover
Development of the SSO feature is an incremental step within an overall program to improve the
availability of networks constructed with Cisco IOS XE switches.
In specific Cisco networking devices that support dual supervisor engines, SSO takes advantage of
supervisor engine redundancy to increase network availability. SSO achieves this by establishing one of
the supervisor engines as the active processor while the other supervisor engine is designated as the
standby processor. Following an initial synchronization between the two supervisor engines, SSO
dynamically synchronizes supervisor engine state information between them in real-time.
A switchover from the active to the standby supervisor engine occurs when the active supervisor engine
fails or is removed from the networking device.
Cisco NSF is used with SSO. Cisco NSF allows the forwarding of data packets to continue along known
routes while the routing protocol information is being restored following a switchover. With Cisco NSF,
peer networking devices do not experience routing flaps, which reduce loss of service outages for
customers.
Figure 6-1 illustrates how SSO is typically deployed in service provider networks. In this example,
Cisco NSF with SSO is enabled at the access layer (edge) of the service provider network. A fault at this
point could result in loss of service for enterprise customers requiring access to the service provider
network.

Cisco Catalyst 4500 Series Specifications

General

Series	Catalyst 4500 Series
Category	Switch
Layer Support	Layer 2, Layer 3
Form Factor	Modular chassis
Stackable	No
Chassis Slots	3, 6, 7, 10
Power Supply Options	AC, DC
Redundancy	Power supply, Supervisor engine
Network Management	Cisco IOS Software CLI, SNMP, Cisco Prime Infrastructure
Features	Security, QoS
Port Density	Up to 384 ports per chassis
Security Features	802.1X, ACLs, DHCP Snooping, Dynamic ARP Inspection, IP Source Guard
Supervisor Engine	8-E