How to Replace Your Old Router with a Cisco ISR4321/ISR4331/ISR4431/ISR4461 (Zero-Drama Migration Guide)
Answer first: ISR 4000 replacement is a controlled change, not a copy-and-paste task. Inventory the old functions, confirm the target PID and lifecycle, translate interfaces and policies, pre-stage, back up, define rollback, and test acceptance criteria. Use the official lifecycle page, data sheet, and ISR FAQ hub, ...