About Performing Issu - Cisco Catalyst 4500 Series Configuration Manual

Chapter 6 Configuring the Cisco IOS XE In Service Software Upgrade Process
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About Performing ISSU

Note Do not make any hardware changes while performing ISSU.
Before you perform ISSU, you should understand the following concepts:
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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
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.
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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
the Boot Field and Using the boot Command, page
If you enter the no ip routing command, ISSU falls back from SSO to RPR mode, resulting in traffic
loss.
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
illustrates how SSO is typically deployed in service provider networks. In this example,
3-27.
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
About Performing ISSU
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