Cisco IOS Explained with Features and Functions

The Cisco IOS (Internetwork Operating System) is a proprietary operating system that provides routing, switching, and internetworking features. It controls and manages the hardware on which it runs. Technically, it provides an interface between a user and the hardware, allowing the user to execute commands to configure and manage the Cisco device. Initially, Cisco developed IOS for its routers. Later, it redesigned it to work on other devices such as switches and firewalls. Currently, it works on all supported Cisco devices.

Functions of IOS

IOS is responsible for the following functions: -

• To carry network protocols and functions
• To connect different data link layer technologies
• To transfer data between devices at the highest possible speed
• To secure network resources
• To control unauthorized access
• To provide scalability for ease of network growth
• To keep the network stable and reliable

Features of IOS

IOS provides scalability, connectivity, reliability, and security.

Scalability

Cisco makes routers and switches across two hardware platforms: fixed-chassis and modular-chassis. A fixed-chassis device does not support interface changes. You must use it as it is. You cannot add any additional interfaces to it. Similarly, you cannot remove any existing interfaces. The following image shows a fixed chassis router.

A modular-chassis device allows you to customize interfaces as needed. It comes with slots. A slot will enable you to install and use any supported interface. If required, you can also remove or replace any existing interfaces from slots. The following image shows a modular chassis router and modular interfaces.

The modular chassis platform provides more flexibility but costs more than the fixed chassis platform. Cisco creates separate versions of IOS for both platforms. A fixed-chassis IOS omits the features required for a modular-chassis device. Since Cisco uses customized versions of IOS, you never need to pay for features you do not use.

Connectivity

Each media type uses a separate format for data transfer. IOS understands the formats of almost all modern media types and converts them as needed. You can use an IOS running router to connect two different networks that use various media types, such as: -

• To connect a LAN network to a WAN network
• To connect a wireless network to a wired network.

Reliability

The first IOS was written in 1986 by William Yeager. Since then, to keep the IOS up to date, ensure critical resources remain accessible, and adopt new technologies introduced to the market, Cisco has tweaked and tuned the IOS several times and added new features with every update. Because of the success of its IOS software, Cisco has moved from a garage-router company to one of the world's largest companies in less than two decades. Nowadays, a large portion of the Internet backbone is composed of Cisco products. Due to reliability and stability, most enterprise networks, as well as ISPs, use Cisco products in some form.

Security

The IOS includes a wide range of security features that allow you to control your network resources and devices in accordance with your internal security policies. You can configure it to allow or deny a specific host or a range of hosts. You can also configure it to allow or deny access to a particular application. Once security policies, commonly known as access control lists, are configured, IOS actively monitors all traffic that passes through it and allows or denies it based on the configured rules. For example, if it receives traffic from a host blocked in the access list, it discards it immediately. If it gets traffic from a host allowed in the access list, it processes it and forwards it to the destination.

Conclusion

Cisco IOS is a powerful and versatile operating system that plays a vital role in the functioning of Cisco networking devices. It manages routing, switching, and internetworking to ensure seamless communication across different networks. The continuous updates and enhancements over the years have made IOS a reliable choice for both small and large-scale networks. With its distinct features such as scalability, connectivity, reliability, and security, Cisco IOS accommodates a wide range of networking needs.