Symptom

When downgrading routers from 17.1.1, 16.12.2, 16.9.4 etc to older releases such as 3.18 SP, 3.16 SP etc. Router is going into a continuous boot-loop.

Conditions

Following logs will be displayed during bootup : FPGA UPGRADE Done: System going for reboot System Bootstrap, Version 15.6(10r)S, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 2016 by cisco Systems, Inc. Compiled Thu 24-Mar-16 15:38 by alnguyen Boot ROM1 Last reset cause: PowerOn UEA platform with 3670016 Kbytes of main memory

Workaround

Further Problem Description

ASR903/902-RSP2 and ASR 920 routers do not support a rollback , from Cisco IOS XE Versions3.18SP7, 16.6.7, 16.9.4, 16.12.1 and later to previous versions. If a rollback is attempted , the secure boot logic will detect tampering and set the router into a continuous boot loop.