Symptom

Cat9500-[12Q||24Q||16X||40X] will reset ROMMON variables to default values upon downgrade from 16.12.1 or later release to 16.6.[1-6] upon subsequent reboot Initializing Hardware... SNP: failed to initialize MAC address (not found/zero) Please set a value for MAC_ADDR and restart the device before proceeding Both copies of Nvram are corrupted. Warning: monitor nvram area is corrupt ... using default values System Bootstrap, Version 17.1.1r, RELEASE SOFTWARE (P) Compiled Wed 08/21/2019 8:52:37.90 by rel Current ROMMON image : Primary Last reset cause : CpuReset C9500-40X platform with 16777216 Kbytes of main memory Setting MODEL_NUM [C9500-40X] Setting SYSTEM_SERIAL_NUM [FCW2215XXXX] Setting MOTHERBOARD_SERIAL_NUM [FOC2214XXXX] Setting VERSION_ID [V01] Setting MOTHERBOARD_REVISION_NUM [B0] Setting MOTHERBOARD_ASSEMBLY_NUM [73-18140-03] Setting MODEL_REVISION_NUM [C0] WARNING: Bootable URL's in BOOT variable not found or exhausted. Please check the ROMMON configuration or boot command usage.

Conditions

Cat9500-12Q or Cat9500-24Q or Cat9500-16X or Cat9500-40X IOS downgrade from 16.12.1 or later to 16.6.1 // 16.6.2 // 16.6.3 // 16.6.4 // 16.6.5 // 16.6.6 release

Workaround

Further Problem Description

This issue is seen because starting from 16.12.1 onward we have introduced BIOS-protected ROMMON which was not supported on 16.6.x software train until 16.6.7 and later Further Recommendation Not to recommend downgrade from 16.12.1 onwards release to an IOS Release ranging from 16.6.1 to 16.6.6 release. Issue will not be seen when downgrading to 16.6.7 onwards releases.