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The time has come to introduce you to the Cisco Internetwork
Operating System (IOS). The IOS is what runs Cisco routers as
well as Cisco’s switches, and it’s what allows you to configure
the devices as well.
So that’s what you’re going to learn about in this chapter. I’m going to show you how to
configure a Cisco IOS router using the Cisco IOS command-line interface (CLI). When you
become proficient with this interface, you’ll be able to configure hostnames, banners, passwords,
and more, as well as troubleshoot using the Cisco IOS.
From there, we’ll take a peek at Cisco’s Security Device Manager (SDM) and you’ll find
out how to set up a secure HTTPS session to a router to provide the same types of configurations.
The SDM really becomes a much more powerful tool in more advanced topics because
it makes configuring access lists, virtual private networks (VPNs), and IP Security (IPSec) a
snap, but first, you need to learn the basics of Cisco’s IOS.
I’m also going to get you up to speed on the vital basics of router configurations and
command verifications. Here’s a list of the subjects we’ll be covering in this chapter:
Understanding and configuring the Cisco Internetwork Operating System (IOS)
Connecting to a router
Bringing up a router
Logging into a router
Understanding the router prompts
Understanding the CLI prompts
Performing editing and help features
Gathering basic routing information
Setting administrative functions
Setting hostnames
Setting banners
Setting passwords
Setting interface descriptions
Performing interface configurations
Viewing, saving, and erasing configurations
Verifying routing configurations
The IOS User Interface
181
And just as it was with preceding chapters, the fundamentals that you’ll learn in this chapter
are foundational building blocks that really need to be in place before you go on to the next
chapters in the book.
For up-to-the-minute updates for this chapter, please see
www.lammle.com
and/or
www.sybex.com/go/ccent
.
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.
In the following sections, I’ll show you the Cisco IOS and how to configure a Cisco router
using the command-line interface (CLI). We’ll use Cisco’s SDM toward the end of the chapter.
I’m going to save Cisco switch configurations for Chapter 7, “Layer 2
Switching.”
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 everincreasing
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
You can access the Cisco IOS through the console port of a router, from a modem into the
auxiliary (or Aux) port, or even through Telnet. Access to the IOS command line is called an
EXEC session
.
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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 may or may not be a password set. The new ISR routers use
cisco
as the username and
cisco
as the password by default.
See Chapter 1, “Internetworking,” for an explanation of how to configure a
PC 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. 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.
Figure 4.1 shows an illustration of a 2501 Cisco router. Pay close attention to all the
different kinds of interfaces and connections.
FIGURE 4 . 1
A Cisco 2501 router
The 2501 router has two serial interfaces, which can be used for WAN connections, and one
Attachment Unit Interface (AUI) connection for a 10Mbps Ethernet network connection. This
router also has one console and one auxiliary connection via RJ-45 connectors. The 2501 router
shown has two serial V.35 connections used for WAN connections like a T1, or Frame Relay.
Plus, next to the console port could be another RJ45 port marked as BRI (Basic Rate Interface)
that’s used with ISDN (Integrated Services Digital Network). And don’t stress—I’m going to
cover T1, Frame Relay, ISDN, and more WAN protocols coming up in Chapter 10, “Introduction
to Wide Area Networks.”
Figure 4.2 shows an illustration of a Cisco 2600 series modular router, which is a cut above
routers populating the 2500 series because it has a faster processor and can handle many more
interfaces. Both the 2500 and 2600 series routers are end of life (EOL), and you can only buy
them used. However, many 2600 series routers are still found in production, so it’s important
to understand them. Pay close attention to all the different kinds of interfaces and connections.
AUI SERIAL 0 SERIAL 1 CONSOLE AUX
CISCO 2501
Input: 100-240VAC
Freq: 50.60 Hz
Current: 1.2-0.6A
Watts: 40W
The IOS User Interface
183
FIGURE 4 . 2
A Cisco 2600 router
The 2600 series router can have multiple serial interfaces, which can be used for connecting
a T1 or Frame Relay using a serial V.35 WAN connection. Multiple Ethernet or FastEthernet
ports can be used on the router, depending on the model. This router also has one console and
one auxiliary connection via RJ-45 connectors.
Another router I want to talk about is the 2800 series (shown in Figure 4.3). This router has
replaced the 2600 series router series and is referred to as an Integrated Services Router (ISR).
It gets its name because many of the services, like security, are built into it. It’s a modular
device like the 2600, but it’s much faster and a lot more sleek—it’s elegantly designed to
support a broad new range of interface options.
FIGURE 4 . 3
A Cisco 2800 router
I mentioned that security is built in—the 2800 has the Security Device Manager (SDM) preinstalled.
The SDM is a Web-based device-management tool for Cisco routers that can help you
configure a router via a web console. I’ll cover that later in this chapter. You need to keep in
mind that for the most part, you get some serious bang for your buck with the 2800—unless you
start adding a lot of interfaces to it. You’ve got to pony up for each one of those little beauties,
and things can really start to add up—fast!
There are a couple of other series of routers that are less expensive than the 2800 series: the
1800 and 800 series. You may want to look into these routers if you’re looking for a less-expensive
alternative to the 2800 but still want to run the same 12.4 IOS and the latest SDM.
Figure 4.4 shows an 1841 router that holds most of the same interfaces as the 2800, but it’s
smaller and less expensive. The real reason you would opt for a 2800 instead of an 1800 series
router comes down to the more advanced interfaces you can run on the 2800—things like the
wireless controller and switching modules.
FIGURE 4 . 4
A Cisco 1841 router
Cisco 2610 router
ETHERNET 0/0
LINK ACT
LOCK
BACK
CONSOLE AUX
CISCO 2610
100–240VAC
1.2–0.6A
Console port (RJ-45)
Ethernet 0/0
10BaseT port (RJ-45) Auxiliary port (RJ-45)
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As a heads up, I'm going to be using all new 2800, 1800, and 800 series routers throughout
this book to demonstrate examples of router configurations. But understand that you can use
the 2600 and even 2500 routers to practice routing principles.
You can find more information about all Cisco routers at
www.cisco.com/en/
US/products/hw/routers/index.html
.
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
This is the first part of the router boot process output. It’s information about the bootstrap
program that first runs the POST. It then tells the router how to load, which by default is to
find the IOS in flash memory. It also lists the amount of RAM in the router.
The next part shows us that the IOS is being decompressed into RAM:
program load complete, entry point: 0x8000f000, size: 0x14b45f8
Self decompressing the image :
####################################################################
############################################ [OK]
The pound signs are telling us that the IOS is being loaded into RAM. After it is decompressed
into RAM, the IOS is loaded and starts running the router, as shown below. Notice
that the IOS version is stated as advanced security version 12.4(12):
[some output cut]
Cisco IOS Software, 2800 Software (C2800NM-ADVSECURITYK9-M), Version
12.4(12), RELEASE SOFTWARE (fc1)
The IOS User Interface
185
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2006 by Cisco Systems, Inc.
Compiled Fri 17-Nov-06 12:02 by prod_rel_team
Image text-base: 0x40093160, data-base: 0x41AA0000
A sweet new feature of the new ISR routers is that the IOS name is no longer cryptic.
The filename actually tells you what the IOS can do, as in Advanced Security. Once the
IOS is loaded, the information learned from the POST will be displayed next, as you can
see here:
[some output cut]
Cisco 2811 (revision 49.46) with 249856K/12288K bytes of memory.
Processor board ID FTX1049A1AB
2 FastEthernet interfaces
4 Serial(sync/async) interfaces
1 Virtual Private Network (VPN) Module
DRAM configuration is 64 bits wide with parity enabled.
239K bytes of non-volatile configuration memory.
62720K bytes of ATA CompactFlash (Read/Write)
There are two FastEthernet interfaces, four serial interfaces, plus a VPN module. The
amount of RAM, NVRAM, and flash are also displayed. The above router output shows us
that there’s 256MB of RAM, 239K of NVARM, and 64MB of flash.
When the IOS is loaded and up and running, a preconfiguration (called startup-config) will
be copied from NVRAM into RAM. The copy of this file will be placed in RAM and called
running-config.
My 1841 and 871W routers boot exactly the same as the 2811 router. The
1841 and 871W do show less memory and different interfaces, but other
than that, they have the same bootup procedure and the same preconfigured
startup-config file.
Bringing Up a Non-ISR Router (a 2600)
As you’re about to see, the boot cycle is about the same for non-ISR routers as for the ISR routers.
The following messages appear when you first boot or reload a 2600 router:
System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
Copyright (c) 1999 by cisco Systems, Inc.
TAC:Home:SW:IOS:Specials for info
C2600 platform with 65536 Kbytes of main memory
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The next part shows us that the IOS is being decompressed into RAM:
program load complete, entry point:0x80008000, size:0x43b7fc
Self decompressing the image :
#######################################################################
#######################################################################
#######################################################################
#######################################################################
#######################################################################
#######################################################################
#######################################################################
## [OK]
So far, everything is pretty much the same. Notice below that the IOS version is stated as
version 12.3(20):
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IK9O3S3-M), Version 12.3(20), RELEASE
SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2006 by cisco Systems, Inc.
Compiled Tue 08-Aug-06 20:50 by kesnyder
Image text-base: 0x80008098, data-base: 0x81A0E7A8
Just as with the 2800 series, once the IOS is loaded, the information learned from the POST
will be displayed:
cisco 2610 (MPC860) processor (revision 0x202) with 61440K/4096K bytes
of memory.
Processor board ID JAD03348593 (1529298102)
M860 processor: part number 0, mask 49
Bridging software.
X.25 software, Version 3.0.0.
1 Ethernet/IEEE 802.3 interface(s)
1 Serial network interface(s)
2 Serial(sync/async) network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)
Okay—finally what we see here is one Ethernet interface and three serial interfaces. The
amount of RAM and flash is also displayed, and the above router output shows there are
64MB of RAM and 16MB of flash.
The IOS User Interface 187
And as I mentioned, when the IOS is loaded and up and running, a valid configuration
called the startup-config will be loaded from NVRAM. But here’s where it differs from the
default bootup of the ISR routers—if there isn’t a configuration in NVRAM, the router will
broadcast looking for a valid one on a TFTP host. (This can only happen if the router senses
carrier detect, or CD, on any interface.) If the broadcast fails, it will then go into what is called
setup mode—a step-by-step process to help you configure the router. So you need to remember
that, if you plug any interface of your router into your network and then boot your router, you
may have to wait a couple minutes while the router searches for the configuration.
You can have your ISR routers perform this boot cycle by erasing the startupconfig
and reloading the router. This will give you a clean router with no
default configuration. I’ll show you how to do this a little later in the chapter.
You can also enter setup mode at any time from the command line by typing the command
setup from something called privileged mode, which I’ll get to in a minute. Setup mode covers
only some global commands and is generally just unhelpful. Here is an example:
Would you like to enter the initial configuration dialog? [yes/no]: y
At any point you may enter a question mark '?' for help.
Use ctrl-c to abort configuration dialog at any prompt.
Default settings are in square brackets '[]'.
Basic management setup configures only enough connectivity
for management of the system, extended setup will ask you
to configure each interface on the system
Would you like to enter basic management setup? [yes/no]: y
Configuring global parameters:
Enter host name [Router]:Ctrl+C
Configuration aborted, no changes made.
You can exit setup mode at any time by pressing Ctrl+C.
I highly recommend going through setup mode once, then never again. You should always
use the CLI or SDM.
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