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

Cisco moving to different operating systems for their networking devices should come as no surprise. When comparing traditional or monolithic IOS to Juniper or Arista, we find IOS lacking. Specifically we find it lacking in the areas of scripting, programing, and just being able to do more.

For the purpose of the CCIE, we should know traditional IOS is considered “monolithic”.

IOS was good for traditional networks however evolving networks with needs for APIs and programmability are on the rise, and IOS can not handle it.

IOS XE, a Linux based operating system created by Cisco for Routers, Switches, and other network appliances fulfills these needs.

IOS XE runs a Linux daemon/service to mimic traditional IOS version 15, keeping you familiar on the command line.


Cisco has created two new terms for this.

Forwarding and Feature Manager (FFM) and Forwarding Engine Driver (FED).

The FFM provides APIs to manage the control plane processes. It programs the data plane through the FED and maintains the states for it. The FED is the code that runs these blades. The FFM is responsible for managing features that you turn on in IOS XE as well as things like the TCAM.

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