An issue of ISSU was encountered during my work which I would like to record here and share with people who encountered similar or exactly the same problem.
My client wished to upgrade a SGA train IOS into SG train IOS, however during the ISSU software upgrade process problem occurred. During ISSU upgrade, the redundancy mode should be in SSO after Loadversion command was executed, but in my case the redundancy mode changed to RPR.
Slot 3 supervisory engine ISSU state
Switch#show issu state detail
RP State = Active
ISSU State = Load Version
Boot Variable = bootflash:cat4500-ipbase-mz.122-31.SGA8.bin,12
Operating Mode = RPR
Primary Version = bootflash:cat4500-ipbase-mz.122-31.SGA8.bin
Secondary Version = bootflash:cat4500-ipbase-mz.122-54.SG1.bin
Current Version = bootflash:cat4500-ipbase-mz.122-31.SGA8.bin
Slot 4 supervisory engine ISSU state
RP State = Standby
ISSU State = Load Version
Boot Variable = bootflash:cat4500-ipbase-mz.122-54.SG1.bin,12;b
ootflash:cat4500-ipbase-mz.122-31.SGA8.bin,12
Operating Mode = RPR
Primary Version = bootflash:cat4500-ipbase-mz.122-31.SGA8.bin
Secondary Version = bootflash:cat4500-ipbase-mz.122-54.SG1.bin
Current Version = bootflash:cat4500-ipbase-mz.122-54.SG1.bin
Compatibility issue
The issue actually lies with IOS compatibility, when Loadversion is executed, supervisory engine will check for compatibility, if not compatible redundancy mode will switch to RPR, otherwise the redundancy mode will be in SSO.
Refer to Cat4500 configuration guide.
This is the clause stated in the guide:
It may take several seconds after the issu loadversion command is entered for Cisco IOS software to load onto the standby supervisor engine and for the standby supervisor engine to transition to SSO mode. This causes the standby supervisor engine to reload with the new image.
If you use the forced option, the standby supervisor engine is booted with the new image. After the image is loaded on the standby supervisor engine, if the image is incompatible, the system is forced to the RPR mode. Otherwise the system will continue in the SSO mode.
It became clear that there are 3 trains for Cat4500 IOS namely SG, SGA and EWA. Refer to this Cisco IOS lifecycle guide. Here’s an important clause from cisco:
Customers requiring the latest Cisco Catalyst 4500 Series hardware and software features should migrate to Cisco IOS Software Release 12.2(31)SGA.
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