Since Cisco announced an intention to unify software version across routing and switch platforms, we have already seen the first software release of Denali 16.1 on Cisco IOS XE switches. Subsequently, Cisco has also released the first common software version between router and switch with Denali 16.2.1. While you can upgrade a switch as you normally would, upgrading a router requires a closer attention. In this article, we will show you how to upgrade an ISR 4000 to Denali 16.2.1. We will be using ISR 4321 running IOS XE 3.6.