Manual

Cisco IOS In Service Software Upgrade Process
Information About Performing ISSU
9
Cisco IOS Release 12.2(28)SB
Then, the former active RP, which is now the new standby RP, is loaded with the new software (see
Figure 5).
Figure 5 Load New Standby RP with New Cisco IOS Software
The two RPs in a system can be in one of three different states during ISSU:
• Active—One RP is actively forwarding packets with old software. After the ISSU process is
performed, the original active RP becomes the standby RP.
• Standby—Perform ISSU on the standby RP, loading it with new software. After the ISSU process is
performed, the original standby RP is the new active RP.
• Hot standby—After the original standby RP becomes the new active RP, load the new software
image into the new standby RP. Doing so makes the standby RP a hot standby RP.
Figure 6 shows the ISSU states during the ISSU process.
Line cards
Active
Route
Processor
Cisco IOS
12.x(y)S
Cisco IOS
12.x(y)S
Cisco IOS
12.x(z)S
Standby is reset and
reloaded with
new software
Cisco IOS
12.x(z)S
Standby
Route
Processor
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