Hardware Installation Guide for Cisco 4000 Series Integrated Services Routers - Overview of the Cisco 4000 Series ISRs [Cisco 4000 Series Integrated Services Routers] - Cisco
Original Cisco 4000 Series Router ISR4351-V/K9 — Network Exp
Cisco 4331 Integrated Services Router - Cisco
New Cisco ISR4221/K9 4000 series Integrated Service Router | Netmode