CCIE 400-101: Network Principles - IOS and IOS XE

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

  • IOS XE is an evolution of IOS.
  • Historically, an overwhelming majority of the internal software processes are run using Cisco IOS memory. 
  • IOS XE introduces a distributed software architecture that moves many operating system responsibilities out of the IOS process. 
  • This architecture allows for better allocation of memory so the router can run more efficiently and allows increased high availability at all times. 
  • IOS XE 15.0 runs as a single daemon within a modern Linux OS. Additional system functions run as separate processes.
  • IOS XE retains the exact same look and feel of IOS, while providing improved functionality.
  • Some of the IOS XE benefits include:
    1. Multi-Core CPU: Running IOS and separate processes enables load balancing the multi-core CPU, each process using a different core.
    2. Control Plane and Data Plane Separation: The Control Plane and Data Plane are separated with the introduction of the Forwarding Feature Manager (FFM) and its standard interface to the Forwarding Engine Driver (FED).
    3. Platform Abstraction: IOS XE allows the platform dependent code to be abstracted from a single monolithic image to move to a more purely protocol independent IOS process.
    4. Application Integration: prior to IOS XE, the only way to integrate functionality into an IOS was to either port the functionality into the IOS or run it as a service blade outside of IOS.

  • The actual IOS XE comes in seven different software modules (sub-packages).
  • Each sub-package provides specific functions:
    1. RPBase provides the operating system software for the Route Processor.
    2. RPControl controls the control plane processes that interface between the IOS process and the rest of the platform.
    3. RPAccess provides software required for router access.
    4. RPIOS provides the Cisco IOS kernel, which is where IOS features are stored and run. Each consolidated package has a different RPIOS.
    5. ESPBase provides the ESP operating system and control processes, and the ESP software.
    6. SIBBase controls the SIP operating system and control processes.
    7. SIPSPA provides the SPA driver and Field Programmable Device (FPD) images.

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