The IOS User Interface
The Cisco Internetwork Operating System (IOS) is the kernel of Cisco routers as well as all current Catalyst switches. In case you didn’t know, a kernel is the elemental, indispensable part of an operating system that allocates resources and manages tasks like low-level hardware interfaces and security.
Coming up, I’ll show you the Cisco IOS and how to configure a Cisco switch using the command-line interface (CLI) . By using the CLI, we can provide access to a Cisco device and provide voice, video, and data service. . . . The configurations you’ll see in this chapter are exactly the
same as they are on a Cisco router.
The Cisco IOS is a proprietary kernel that provides routing, switching, internetworking, and telecommunications features. The first IOS was written by William Yeager in 1986 and enabled networked applications. It runs on most Cisco routers as well as a growing number of Cisco Catalyst switches, like the Catalyst 2960 and 3560 series switches used in this book. And it’s an essential for the Cisco exam objectives!
Here’s a short list of some important things that the Cisco router IOS software is responsible for:
Carrying network protocols and functions
Connecting high-speed traffic between devices
Adding security to control access and stopping unauthorized network use
Providing scalability for ease of network growth and redundancy
Supplying network reliability for connecting to network resources
You can access the Cisco IOS through the console port of a router or switch, from a modem into the auxiliary (or aux) port on a router, or even through Telnet and Secure Shell (SSH). Access to the IOS
command line is called an EXEC session .
Connecting to a Cisco IOS Device
We connect to a Cisco device to configure it, verify its configuration, and check statistics, and although there are different approaches to this, the first place you would usually connect to is the console port. The console port is usually an RJ45, 8-pin modular connection located at the back of the device, and there may or may not be a password set on it by default.
Look back into Chapter 2, “Ethernet Networking and Data
Encapsulation,” to review how to configure a PC and enable it to connect to a router console port.
You can also connect to a Cisco router through an auxiliary port , which is really the same thing as a console port, so it follows that you can use it as one. The main difference with an auxiliary port is that it
also allows you to configure modem commands so that a modem can be connected to the router. This is a cool feature because it lets you
dial up a remote router and attach to the auxiliary port if the router is down and you need to configure it remotely, out-of-band . One of the
differences between Cisco routers and switches is that switches do not have an auxiliary port.
The third way to connect to a Cisco device is in-band , through the program Telnet or Secure Shell (SSH) . In-band means configuring the device via the network, the opposite of out-of-band . We covered Telnet and SSH in Chapter 3, “Introduction to TCP/IP,” and in this chapter,
I’ll show you how to configure access to both of these protocols on a Cisco device.