1.1.a Network Theory – IOS vs IOS XE

IOS is the acronym for Cisco’s Internetworking Operation System, it is the brain (software OS) behind the brawn (Cisco hardware) for the complex tasks of internetworking; managing and controlling the diverse networking hardware resources and functions; modern IOS consists of multiple modular subsystems.

IOSXE improves on IOS by improving portability across platforms and adding extensibility by being built on POSIX (standards for software compatibility with OSes including variants of UNIX)).

From the CCIE R&S v5 written blueprint, we’ve the following questions which requires answering:

1.1.a Describe basic software architecture differences between IOS and IOS XE
1.1.a (i) Control plane and Forwarding plane
1.1.a (ii) Impact to troubleshooting and performances
1.1.a (iii) Excluding specific platform’s architecture

IOS

• For the legacy IOS (or soon to be legacy); it appears there is no control and data plane separation outside of the IOS instance.
• IOS is a single monolithic image containing both Platform dependent (PD, OS service)  and Platform independent programming (PI, routing platform)

R1#show process cpu
R1#show process mem

IOS-XE

• Use of FFM (Forwarding and Feature Manager) and Forwarding Engine Director (FED) accomplishes control and data plane separation on the IOS-XE.  Control plane process is delivered a set of APIs by FFM.  Data Plane is programmed through the use of FED; acting like an hardware driver instance; by the FFM.
• IOS separate Platform dependent and Platform independent programming by moving drivers outside of the IOS code; i.e. allows independent development, packaging of PI software.
• Supports multiple core processors; IOSd is multithreaded process which allows scaling and load-balancing of multiple cores.

R1#show process cpu
R1#show process cpu | include five
R1#show process cpu detailed
R1#show process cpu detailed process iosd
R1#show process mem

References:
http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/ios-xe-3sg/QA_C67-623261.html
http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/ios-xe-3sg/QA_C67-622903.html
http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/ios-xe-3sg/QA_C67-622903.html
http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-110/13327-ios-early.html