Cisco IOS Variations

Cisco IOS (Internetwork Operating System) is the software that runs on Cisco routers and switches. The versioning of Cisco IOS can be a bit complex, but generally, it follows a pattern. Cisco uses different trains, feature sets, and release numbers to differentiate between versions. Here are some key points:

  • Major Release Number (e.g., 12, 15): The major release number represents a major revision of the IOS. New major releases often introduce significant features and improvements.
  • Train Identifier (e.g., Mainline, T, XE, XR): Different trains are designed for different platforms and use cases. For example, the Mainline train is the general release for most platforms, while the XE (Extended Enterprise) train is designed for modular routers.
  • Release Number (e.g., 1, 2, 3): The release number indicates the specific version within a major release and train. Newer release numbers often include bug fixes and minor enhancements.
  • Maintenance Release (e.g., 12.4(15)T5): The maintenance release includes bug fixes and updates for a specific release. The T5 in this example indicates the fifth maintenance release for the 12.4 train.
  • Feature Set (e.g., IP Base, Advanced IP Services): Cisco IOS is available in different feature sets that offer varying levels of functionality. The feature set is often denoted in the version, such as IP Base or Advanced IP Services.
  • Special Releases (e.g., ED, GD, MD): Cisco may use special releases to indicate Early Deployment (ED), General Deployment (GD), or Maintenance Deployment (MD). ED releases may contain new features that are not fully tested, while GD releases are considered stable for most deployments.

Cisco has different operating systems for its various networking devices. Let’s break down the differences between Cisco IOS, IOSd, IOS XE, and IOS XR:

  • Cisco IOS (Internetwork Operating System):
    • Type: Monolithic
    • Devices: Typically used on traditional routers and switches.
    • Architecture: Monolithic architecture, meaning the entire operating system runs as a single image.
    • Characteristics: Historically, Cisco IOS was the standard operating system for Cisco routers and switches. It has a single code base, and updates generally involve replacing the entire image.
  • IOSd (IOS Daemon):
    • Type: Modular
    • Devices: Used in conjunction with Cisco IOS XE.
    • Architecture: IOSd is a modular architecture designed to separate data plane and control plane functions. It allows for better scalability and flexibility.
    • Characteristics: IOSd is part of the IOS XE architecture and is responsible for managing data plane functions. It allows for the independent upgrade of individual components, enhancing flexibility and reducing downtime during updates.
  • IOS XE (IOS Extensible):
    • Type: Modular
    • Devices: Used in modern routers and switches, especially in Cisco ASR (Aggregation Services Routers) and ISR (Integrated Services Routers) platforms.
    • Architecture: IOS XE is based on a modular architecture, separating the control plane and data plane. It incorporates IOSd for data plane functions.
    • Characteristics: IOS XE allows for the independent upgrade of software components, offering enhanced modularity and serviceability. It supports features like in-service software upgrades (ISSU), where updates can be performed without disrupting the network.
  • IOS XR (IOS eXtensible Operating System):
    • Type: Modular
    • Devices: Primarily used in high-end routers like the Cisco CRS (Carrier Routing System) and Cisco ASR 9000 Series.
    • Architecture: IOS XR is designed with a distributed and modular architecture, separating various functions into individual processes running on separate processors (chassis, line cards, and route processors).
    • Characteristics: IOS XR is designed for high-performance, scalability, and reliability. Its distributed architecture allows for better handling of large-scale networks and enables high availability features. It is commonly used in service provider environments.

In summary, Cisco IOS is the traditional monolithic operating system, IOSd is a component within IOS XE for managing data plane functions, IOS XE is a modular operating system for modern routers and switches, and IOS XR is a distributed and modular operating system for high-end routers. The choice depends on the specific requirements and scale of the network deployment.