Even though the Cisco IOS code base comprises of a cooperative multitasking kernel, nearly all of the Cisco IOS features have been moved to different kernels including QNX and Linux for utilization in Cisco products or simulators like Cisco VIRL.

Not all of Cisco’s products run IOS. Prominent exemptions comprise of ASA security products, which run a Linux-derived operating system (OS), and carrier routers which run the IOS-XR.

Cisco IOS User Interface

The Cisco IOS command line interface supplies a permanent set of multiple-worded user commands. The set which is available is identified by the “mode” and the privileged access level of the current user. “Global configuration mode” supplies commands to modify the system’s configuration, and “interface configuration mode” supplies commands to modify the configuration of a particular interface. All commands are allocated a user privilege level, from 0 to 15, and can only be retrieved by users who have the requisite privilege level. Via the CLI, the commands accessible for each privilege level can be demarcated.

Nearly all of the builds of Cisco IOS come with a Tcl interpreter. By utilizing the Embedded Event Manager feature, the interpreter can be scripted to respond to happenings inside the network environment, like interface failure or periodic timers.

The available command modes comprise some of the below:

  • User EXEC Mode
  • Privileged EXEC Mode
  • Global Configuration Mode
  • ROM Monitor Mode
  • Setup Mode

Please note that in excess of one hundred configuration modes and sub modes are available.

Cisco IOS Versioning

Cisco IOS is versioned by utilizing three numbers and a few letters, the general form a.b(c.d)e, where:

  • a indicates the major version number
  • b indicates the minor version number
  • c indicates the release number, which commences at one and increases as the new releases in a same method a.b train are released. Just so you know, “Train” is Cisco-verbiage meaning, “a vehicle for providing Cisco software to a particular set of platforms and features.”
  • d (excluded from general releases) indicates the interim build number
  • e (0, 1 or two letters) indicates the software release train identifier, for example 0 (which identifies the mainline), T (indicating Technology), E (indicating Enterprise), S (indicating Service provider), XA indicating a special functionality train, XB indicating a differentiated special functionality train, and so on.

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