Earlier this year, Cisco announced replacement switches to the 1841/2800/3800 routers. The older routers have not entirely reached end of sale, but the newer routers (1941/2900/3900) offer big changes in router licensing.
Why is it different? Similar to a PIX or ASA, the new routers use license keys and a universal image to determine the available features. This new licensing scheme shows a clear difference between the version of IOS installed and the feature set installed. You can change them independently and they don’t afect each other.
The license structure has