The IOS User Interface

The Cisco Internetwork Operating System (IOS) is the kernel of Cisco routers and most switches. In case you didn’t know, a kernel is the basic, indispensable part of an operating system that allocates resources and manages things such as low-level hardware interfaces and security.

Cisco Router IOS

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 it enabled networked
applications. It runs on most Cisco routers as well as an ever-increasing number of Cisco Catalyst switches, like the Catalyst 2950/2960 and 3550/3560 series switches.



These are 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 stop unauthorized network use
• Providing scalability for ease of network growth and redundancy
• Supplying network reliability for connecting to network resources

Connecting to a Cisco Router

You can connect to a Cisco router to configure it, verify its configuration, and check statistics.
There are different ways to do this, but most often, the first place you would connect to is
the console port. The console port is usually an RJ-45 (8-pin modular) connection located at the
back of the router—by default, there’s may or may not be a password set. The new ISR routers use cisco as the username and cisco as the password by default.

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. But an auxiliary port also allows you to configure modem commands so that a modem can be connected to the router.
This is a cool feature—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 out-of-band (meaning out of the network).

The third way to connect to a Cisco router is in-band, through the program Telnet ( In-band means configuring the router through the network, the opposite of “out-of-band.”)Telnet is a terminal emulation program that acts as though it’s a dumb terminal. You can use Telnet to connect to any active interface on a router, such as an Ethernet or serial port.

 Bringing Up a Router

When you first bring up a Cisco router, it will run a power-on self-test (POST). If it passes, it will then look for and load the Cisco IOS from flash memory—if an IOS file is present. (Just in case you don’t know, flash memory is electronically erasable programmable read-only memory—an EEPROM.) After that, the IOS loads and looks for a valid configuration—the startup-config—that’s stored in nonvolatile RAM, or NVRAM.

The following messages appear when you first boot or reload a router (I am using my 2811 router):

System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 2006 by cisco Systems, Inc.
Initializing memory for ECC
c2811 platform with 262144 Kbytes of main memory
Main memory is configured to 64 bit mode with ECC enabled
Upgrade ROMMON initialized
program load complete, entry point: 0x8000f000, size: 0xcb80
program load complete, entry point: 0x8000f000, size: 0xcb80