The Cisco Internetworking Operating System (IOS) is a sophisticated
operating system optimized for internetworking. Cisco IOS® provides the
unifying principles around which an internetwork can be maintained
cost-effectively over time. It is a software architecture, disassociated from
hardware, that can be dynamically upgraded to adapt to changing technologies
(hardware and software) as they evolve within a networking infrastructure.
Cisco IOS can be thought of as an internetworking brain, a highly intelligent
administrator that manages and controls complex, distributed network resources
There are no specific requirements for this document.
This document is not restricted to specific software and hardware
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The early releases of Cisco IOS grew into a singular, monolithic system
that is fundamentally router-centric. It was arranged as a set of procedures,
allowing any of the procedure(s) to call any other. This monolithic structure
did not enforce data hiding. Most of its operating code had structural and
Cisco IOS releases 9.21 through 11.2 represent engineering efforts to
redesign Cisco IOS into modular components or subsystems. Organized as a set of
layers, each subsystem now provides an independent entry point into the system
code. The subsystems themselves are defined as discrete modules that support
various functions within the embedded (Kernel) system. This layered subsystem
design has allowed engineering to partition Cisco IOS into more manageable and
easily upgradeable feature sets.
The Cisco IOS evolution to port-ready status indicates that Cisco IOS
11.3 and later can be more easily ported to new platforms. Bulletproofing, a
synonym for still finer levels of modularity, allows Cisco IOS features to be
defined tightly with little to no dependencies on other features or subsystems.
Bulletproofing allows Cisco IOS feature/solution sets to be built specifically
to customer requirements. As Cisco IOS continues to evolve, customers will be
able to mix and match specific features to meet the requirements of their
Cisco IOS 8.3 was the last popular Cisco IOS release before the
Cisco IOS 9.1 first customer shipped (FCS) in December
Cisco IOS 9.1(16) is the last maintenance release of Cisco IOS 9.1.
Cisco IOS 9.1 users were notified that, as of April 17, 1995, they should
upgrade to Cisco IOS 10.0(9) or 10.2(5). Cisco IOS 9.17 has reached its end of
sales (EOS) and end of maintenance (EOM) milestones. Cisco IOS 9.17(16) is the
last maintenance release of 9.17. No more features or bug fixes were to be
applied to the Cisco IOS 9.17 line.
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