Cisco ISR 4321 upgrade from 3.16.04b to 17.12.5aMD or 17.9.7aMD

[jaheshkhan]

One of our customer needs to ugrade Cisco ISR 4321 to current stable version as part of MS teams integration.
Details are as follows:
firmware isr4300-universalk9.03.16.04b.S.155-3.S4b-ext.SPA.bin
it seems its not running in install mode.

what Im seeing as per current stable version it should upgrade from 3.16.04b to 17.12.5aMD or 17.9.7aMD.

is there any upgrade path required? is it required to upgrade Rommon version also?

how many reboot can  expect in this scenario?

may I know the difference between these two stable version - 17.12.5aMD and 17.9.7aMD?

After that they need to install cube and securityK9 license also. would like to know that procedure also

[balaji.bandi]

You need to upgrade ROMMON, then follow the matrix upgrade :

ROMMON Compatibility Matrix

https://www.cisco.com/c/en/us/td/docs/routers/access/4400/cpld/isr4400_hwfp.html

[jaheshkhan]

but how to get upgrade path for this?

[Leo Laohoo]

The router will need to be upgraded to either 17.6.X or 17.9.X before making the final jump to 17.12.X (and later).   This information is not documented.  

Failure to heed above warning will cause the router to go into a boot-crash-loop.  

Cisco ISR & ASR 1k Routers: IOS-XE/Firmware Upgrade (Install Mode)