Cisco Cisco IOS Software Release 12.2(27)SBC

© 2006 Cisco Systems, Inc. All rights reserved.

GLBP supports In Service Software Upgrade (ISSU). In Service Software Upgrade (ISSU) allows a 
high-availability (HA) system to run in Stateful Switchover (SSO) mode even when different versions 
of Cisco IOS software are running on the active and standby Route Processors (RPs) or line cards.

ISSU provides the ability to upgrade or downgrade from one supported Cisco IOS release to another 
while continuing to forward packets and maintain sessions, thereby reducing planned outage time. The 
ability to upgrade or downgrade is achieved by running different software versions on the active RP and 
standby RP for a short period of time to maintain state information between RPs.

This feature provides customers with the same level of HA functionality for planned outages due to 
software upgrades as is available with SSO for unplanned outages. That is, the system can switch over 
to a secondary RP and continue forwarding packets without session loss and with minimal or no packet 
loss. This feature is enabled by default.

Configuration information is included in the 

Cisco IOS In Service Software Upgrade Process

 document.

at the following URL:

Additional information is included in the “Configuring GLBP” module of the Cisco IOS IP Application 
Services Configuration Guide, Release 12.4T

at the following URL:

The following sections provide information about this feature:

ISSU GLBP

For a complete list of features included in the “Configuring GLBP” module, see the Feature Information 
Table located toward the end of the module.

Command reference information is included in the 

Release 12.2SB2 at the following URL: