This article describes about the rollback behaviour in EX4300-MP switch. While trying to rollback from version 21.2R3-S5.4 to 20.2R3-S2.4, Switch went down and VC got broken. Also we have observed kernel errors

Error Logs:
linux_kernel_bde: version magic '3.14.52-rt50-WR7.0.0.9_ovp SMP preempt mod_unload ' should be '3.14.52-rt50-WR7.0.0.9_ovp SMP mod_unload '
linux_kernel_bde: version magic '3.14.52-rt50-WR7.0.0.9_ovp SMP preempt mod_unload ' should be '3.14.52-rt50-WR7.0.0.9_ovp SMP mod_unload '

This issue might be seen if the following conditions are met:

• On EX4300-MP platforms only
• When request system software rollback is performed

Cause:

Rollback functionality loads both kernel and non-kernel (including Junos) component from previous upgrade. But at times when there is significant difference in the kernel component between releases, rollback misses out on some kernel files during rollback. This results in linux going out of sync with the "kernel files" after rollback. Leading to the kernel logs and dcpfe VC-master-Node core dump seen during the rollback.

Conclusion :

If the kernel images across the JUNOS releases between which rollback was performed is different. And rollback failing is a limitation on platform and resulting from how different kernel images are being handled and rollback cannot be performed when there is difference in kernel image - and this is a limitation.

Workaround

• Perform a normal downgrade in order to revert to previous JUNOS
• This Bug is resolved in Versions: 21.2R3-S1, 21.4R3, 22.3R1.
   

First_Draft: 2023-07-03
2023-07-06: Modified Visibility, Description, Solution & KCS Validation