IOS - Internet Operating System
*** for details on recent IOS releases, see the Cisco IOS Software Collateral Library
The Cisco IOS is the brains of the router. It is software that operates the basic functions of the router, and connects the user, the CPU, and the cards together intelligently. The IOS is the underlying operating system of the router, and includes numerous low-level software routines to keep the router functioning.
The Cisco IOS is similar to other OS's, such as computer operating systems - DOS, Windows, UNIX, LINUX, etc. The IOS offers so much that it is impossible to describe it all . . . it allows configuration commands to be entered by the user via an external console, converts them to code, and stores the code in DRAM. The stored commands, as a whole, are called the "config". The IOS is in charge of the config and how this will affect the operation of the router. It also takes that config, and sends commands to the CPU, cards, and modules - telling them how they should deal with incoming and outgoing packets.
The IOS is not the Config !! The config is simply a set of stored parameters and is created from commands entered by the user. The IOS executes those parameters.
The IOS defines what features and routing protocols are available - such as HSRP, RIP, OSPF, etc. The user can configure the router to use RIP, but the IOS executes the RIP. Keep in mind that the CPU and cards do have limited intelligence built-in and they can perform basic functions with their buffers, memory, and registers - but they need a central authority to tell them HOW to deal with data. The IOS is the central authority - it connects everything together.
*** see also The ABC's of IOS Releases
Release Numbering
There are three events that determine the numbering scheme for every release:
• Release maintenance
• Release rebuilds
• Interim builds
Release maintenance (or Maintenance Release) is a scheduled revision of Cisco IOS Software that introduces new features and/or bug fixes, depending on the type of release. For example (Figure 6), the formal numbering scheme for the Release 12.2 family is Release 12.2(n), where `n’ represents the release maintenance number. So, Release 12.2(6) represents the 6th instance of release maintenance.
Release Rebuild (such as a "New Technology Release") - a numeric suffix outside the parenthesis of a release name, such as 12.2(11)T1, indicates a rebuild of a New Technology Introduction release. Please note that there can be several rebuilds of the same revision. For example: Releases 12.2(6a), 12.2(6b), 12.2(6c) OR 12.2(11)T1, 12.2(11)T2, and 12.2(11)T3.
Interim Builds - this is an IOS build from an internal Cisco engineering build process. The Cisco Technical Assistance Center (TAC) provides this for customers to use on a temporary basis to address a specific issue. This type of IOS release is identified by a decimal after the Release Maintenance identifier - the example below is Release 12.2(3.1).
Release Categories
The Cisco IOS software release process has three categories of release: early deployment release (ED), major release, and general deployment release (GD).
ED releases provide advanced networking technologies to customers, for delivery of leading-edge Internet applications. ED releases offer new software capabilities, new platforms, and interface extensions. Customers for whom receiving a new feature is critical to their competitive advantage will benefit from ED releases.
Figure 1: Cisco IOS Software Release Life Cycle
ED releases are designed to deliver specific capabilities and features, and are to be deployed selectively, where needed. Because they have a limited life cycle, ED releases are best suited for deployment in a controlled environment, and should be updated to a major release when it becomes available.
Cisco developed the following special ED releases to meet specific customer and business needs:
The next step in the Cisco IOS software life cycle is the major release, which unifies the features, platforms, functionality, and technology from early deployment releases. The emphasis is on stability and reliability. Subsequent maintenance releases [for example, Release 12.1(3)] do not change the functionality and platform support of the major release, but provide continuous improvement and greater quality, leading ultimately to general deployment.
Major releases are driven to achieve GD certification, which is awarded to Cisco IOS software releases that have had extensive market exposure in a wide range of network environments. They have been qualified through extensive metrics that analyze stability and software defect trends, as well as customer-satisfaction surveys.
At some point, GD releases are replaced by newer releases with the latest networking technologies. Therefore, a release retirement process has been established with three principal milestones: End of Sales (EOS), End of Engineering (EOE), and End of Life (EOL).
EOS - End Of Sales - for major releases, the EOS date is three years after the First Commercial Shipment (FCS) date. This sets a final date for which the release can be purchased for new systems. The EOS release continues to be available for downloading from Cisco Connection Online (CCO) for maintenance upgrades.
EOE - End Of Engineering - the EOE release is the last maintenance release for the GD release, and typically follows about three months after the EOS release. Customers may continue to receive technical support from the Cisco Technical Assistance Center (TAC), as well as download the EOE release from CCO.
The product bulletin announcing the EOS and EOE releases and dates is published one year before the planned EOS date. At this time, customers should begin to investigate upgrading their Cisco IOS software to take advantage of the latest networking technologies.
EOL - End Of Life - at the end of the release life cycle, all support for the Cisco IOS software release is terminated and no longer available for downloading on the EOL date. In general, the EOL date is five years after the EOE date. An EOL product bulletin is published approximately one year prior to the actual EOL date.
| Feature | Benefit |
|---|---|
| Early Deployment Releases | |
| T Release |
Provides early adopters with advanced capabilities and is consolidated into the next major release |
| X Release |
Provides the earliest access to new hardware and software features in advance of consolidating the new functionality in a T release |
| E Release |
Special release for critical time-to-market technologies enterprise application |
| S Release |
Special release for network core applications |
| Major Release |
Provides a stable software platform |
| General Deployment Release |
Provides a high-quality level software platform |