Cisco Internetwork Operating System

Cisco IOS is a proprietary operating system developed by Cisco System for cisco device. It includes all necessary features required by routers and switches including, routing protocols, security features, and access control lists. It is stored in flash memory and transferred into the RAM during the boot process. IOS controls and manages the device on which it is running. Basically it provides the platform to execute the commands to configure and manage the device.

Advantage of IOS

Originally Cisco developed IOS for routers. Success of IOS makes Cisco to implement it in its other platforms including Catalyst switches. IOS provides following advantages:-

Connectivity

IOS connects various type of data link layer technologies together including Ethernet, Fiber and WAN. It provides interoperability between twisted pair and optical fiber, between LAN and WAN media, between branch office and company server, between Novell NetWare and IBM SNA, between UINX and Novell, and many more. IOS supports more protocols than any other internetwork supplier in industry.

Scalability

IOS is scalable for all level of internetworks as organization. It supports both fixed and modular chassis platforms to reduce the management cost. It supports scalable routing protocols that help in overcoming inherent protocol limitations. Other services like protocol termination and translation, filtering, smart broadcasting builds a flexible and scalable infrastructure that keep pace with evolving network requirements.

Reliability

Cisco IOS is the most reliable and innovative OS that enhance applications availability by finding performance-optimal paths and quickly routing traffic around any network failures. Cisco continuously upgrades IOS features to provide network redundancy.

Security

Security is the top priority in IOS. IOS includes many dedicate features for security. With advance security features, you can control access to your network and networking devices in accordance with your organizations security policies.

IOS Naming Conventions

In first instance all IOS look like same. Navigation between access levels and many of management commands are performed in the same way on all IOS products. This might confuse to beginner, as specific command for a particular feature is the same on all IOS products, but configuring another feature might different between router and switch. Cisco sells different flavors of its IOS software for routers and switches depending on the features that it need. In addition to customer need Cisco also makes product specific IOS. This lead differences between different products, some commands work on some routers but not on others.

So before you start working with IOS, it is always a good idea to check its version number and platform. A single command can get all this information including model number, types of interfaces, amount of memory, software version, and configuration setting. Use "show version" command to get all these details.

Router stores IOS in flash memory. You can also use "show flash" command to know the available IOS.

Form the output of above commands we know that router has a IOS of following name

c1841-advipservicesk9-mz.124-6.T7.bin

Let's break this name for clarify. An IOS filename is broken down into four parts:

• Platform
• Feature set
• Run location and compression
• Version

c1841

c1841 is the platform on which IOS will run. From earlier section of this article we know that different devices have different hardware architecture, and a IOS complied for one device may not run on another device. c1841 indicates that, this IOS is complied for 1841 series router.

advipservicesk9

advipservicesk9 indicates the features provided by this IOS. As we have already discussed that different IOS are complied to solve different purpose. This IOS provides advanced IP services for security purpose and k9 refers to the inclusion of encryption support.

mz

mz refers compression. It indicates that the IOS image is compressed and must be uncompressed before running. You may see letter l here, that indicates where IOS image is run from.

124-6.T7

The 124-6.T7 is the version number of IOS. Images names with T indicate new features, and without the T the mainline (only bug fixes are made to it).

.bin

.bin indicates that this is a binary image.

Let's take one more example of IOS name C2500-D-L.120-9.bin.

we could break it down as follows:

1. Platform: C2500
2. Feature Set: D
3. Run Location: L
4. IOS Version: 12.0-9

Now we know the naming conventions used in IOS image. For CCNA exam you do not need to know the feature set code, however you need to know the naming conventions used in IOS filename ( platform, feature set, compression/run location, and version).

IOS naming conventions cheat sheet

IOS Feature set codes

Feature Set code	Description
I	IP
IS	IP PLUS
J	Enterprise
JS	Enterprise Plus
JK8S	Enterprise Plus with IPSec

IOS Run Locations

Code	Memory Location
F	Image runs in flash
M	Image runs in Random Access Memory (RAM)
R	Image runs in Read Only Memory (ROM)
L	Image will be relocated at runtime

IOS Compression Identifiers

Code	Compression
Z	Image is Zip compressed
X	Image is Mzip compressed
W	Image is Stac compressed