12 Facts About Cisco IOS

Cisco IOS network operating system was created from code written by William Yeager at Stanford University, which was developed in the 1980s for routers with 256 kB of memory and low CPU processing power.

Cisco IOS acquired a number of young companies that focused on network switches, such as the inventor of the first Ethernet switch Kalpana, and as a result Cisco switches did not initially run IOS.

Cisco IOS eventually introduced the native mode for chassis, so that they only run one operating system.

Cisco IOS has a monolithic architecture, owing to the limited hardware resources of routers and switches in the 1980s.

Cisco IOS considers each process a single thread and assigns it a priority value, so that high priority processes are executed on the CPU before queued low priority processes, but high priority processes cannot interrupt running low priority processes.

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Disadvantage of the Cisco IOS architecture is that it increases the complexity of the operating system, data corruption is possible as one process can write over the data of another, and one process can destabilize the entire operating system or even cause a software-forced crash.

Cisco IOS recommend upgrading to Maintenance releases where possible, over Interim and Rebuild releases.

Cisco recommends that all Cisco IOS devices implement the authentication, authorization, and accounting security model.

Cisco IOS had already issued a patch, but asked that the flaw not be disclosed.

Cisco IOS filed a lawsuit, but settled after an injunction was issued to prevent further disclosures.

Cisco's response was to develop a tree of Cisco IOS that offered modularity and memory protection between processes, lightweight threads, pre-emptive scheduling and the ability to independently restart failed processes.

In 2006 Cisco introduced IOS Software Modularity, which extends the microkernel architecture into the IOS environment, while still providing the software upgrade capabilities.