1.1.a Describe basic software architecture differences between IOS and IOS XE

1.1.a [i] Control plane and Forwarding plane

IOS XE allows development of data plane ASICs outside the IOS instance and have them program to a set of standard APIs which in turn enforces Control Plane and Data Plane processing separation. It achieves Control Plane / Data Plane separation through the introduction of the Forwarding and Feature Manager (FFM) and its standard interface to the Forwarding Engine Driver (FED). FFM provides a set of APIs to control plane processes. FFM programs the data plane via the FED and maintains forwarding state for the entire system. The FED is the instantiation of the hardware driver for the data plane.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 806-810).  . Kindle Edition.