Senior Acquisitions Editor: Kenyon Brown Development Editor: Kim Wimpsett

FIGURE 6.1

A Cisco 2960 switch

The 3560 switch I’ll be using in this book looks a lot like the 2960, but it

can perform layer 3 switching, unlike the 2960, which is limited to only

layer 2 functions.

I also want to take a moment and tell you about the 2800 series router

because that’s the router series I’ll be using in this book. This router is

known as an Integrated Services Router (ISR) and Cisco has updated it to

the 2900 series, but I still have plenty of 2800 series routers in my

production networks.

Figure 6.2

shows a new 1900 series router. The new

ISR series of routers are nice; they are so named because many services,

like security, are built into them. The ISR series router is a modular

device, much faster and a lot sleeker than the older 2600 series routers,

and it’s elegantly designed to support a broad new range of interface

options. The new ISR series router can offer multiple serial interfaces,

which can be used for connecting a T1 using a serial V.35 WAN

connection. And multiple Fast Ethernet or Gigabit Ethernet ports can be

used on the router, depending on the model. This router also has one

console via an RJ45 connector and another through the USB port. There

is also an auxiliary connection to allow a console connection via a remote

modem.

FIGURE 6.2

A new Cisco 1900 router

You need to keep in mind that for the most part, you get some serious

bang for your buck with the 2800/2900—unless you start adding a bunch

of interfaces to it. You’ve got to pony up for each one of those little

beauties, so this can really start to add up and fast!

A couple of other series of routers that will set you back a lot less than the

2800 series are the 1800/1900s, so look into these routers if you want a

less-expensive alternative to the 2800/2900 but still want to run the

same IOS.

So even though I’m going to be using mostly 2800 series routers and

2960/3560 switches throughout this book to demonstrate examples of

IOS configurations, I want to point out that the particular router model

you use to practice for the Cisco exam isn’t really important. The switch

types are, though—you definitely need a couple 2960 switches as well as a

3560 switch if you want to measure up to the exam objectives!

You can find more information about all Cisco routers at

www.cisco.com/en/US/products/hw/routers/index.html

.

Bringing Up a Switch

When you first bring up a Cisco IOS device, it will run a power-on self-

test—a POST. Upon passing that, the machine will look for and then load

the Cisco IOS from flash memory if an IOS file is present, then expand it

into RAM. As you probably know, flash memory is electronically erasable

programmable read-only memory—an EEPROM. The next step is for the

IOS to locate and load a valid configuration known as the startup-config

that will be stored in nonvolatile RAM (NVRAM).

Once the IOS is loaded and up and running, the startup-config will be

copied from NVRAM into RAM and from then on referred to as the

running-config.

But if a valid startup-config isn’t found in NVRAM, your switch will enter

setup mode, giving you a step-by-step dialog to help configure some basic

parameters on it.

You can also enter setup mode at any time from the command line by

typing the command

setup

from privileged mode, which I’ll get to in a

minute. Setup mode only covers some basic commands and generally

isn’t really all that helpful. Here’s 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 [Switch]:

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

because you should always use the CLI instead!

Command-Line Interface (CLI)

I sometimes refer to the CLI as “cash line interface” because the ability to

create advanced configurations on Cisco routers and switches using the

CLI will earn you some decent cash!

Entering the CLI

After the interface status messages appear and you press Enter, the

Switch>

prompt will pop up. This is called user exec mode, or user mode

for short, and although it’s mostly used to view statistics, it is also a

stepping stone along the way to logging in to privileged exec mode, called

privileged mode for short.

You can view and change the configuration of a Cisco router only while in

privileged mode, and you enter it via the

enable

command like this:

Switch>

enable

Switch#

The

Switch#

prompt signals you’re in privileged mode where you can both

view and change the switch configuration. You can go back from

privileged mode into user mode by using the

disable

command:

Switch#

disable

Switch>

You can type

logout

from either mode to exit the console:

Switch>

logout

Switch con0 is now available

Press RETURN to get started.

Next, I’ll show how to perform some basic administrative configurations.

Overview of Router Modes

To configure from a CLI, you can make global changes to the router by

typing

configure terminal

or just

config t

. This will get you into global

configuration mode where you can make changes to the running-config.

Commands run from global configuration mode are predictably referred

to as global commands, and they are typically set only once and affect the

entire router.

Type

config

from the privileged-mode prompt and then press Enter to

opt for the default of

terminal

like this:

Switch#

config

Configuring from terminal, memory, or network [terminal]? [

press

enter]

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)#

At this point, you make changes that affect the router as a whole

(globally), hence the term global configuration mode. For instance, to

change the running-config—the current configuration running in

dynamic RAM (DRAM)—use the

configure terminal

command, as I just

demonstrated.

CLI Prompts

Let’s explore the different prompts you’ll encounter when configuring a

switch or router now, because knowing them well will really help you

orient yourself and recognize exactly where you are at any given time

while in configuration mode. I’m going to demonstrate some of the

prompts used on a Cisco switch and cover the various terms used along

the way. Make sure you’re very familiar with them, and always check your

prompts before making any changes to a router’s configuration!

We’re not going to venture into every last obscure command prompt you

could potentially come across in the configuration mode world because

that would get us deep into territory that’s beyond the scope of this book.

Instead, I’m going to focus on the prompts you absolutely must know to

pass the exam plus the very handy and seriously vital ones you’ll need

and use the most in real-life networking—the cream of the crop.

Don’t freak! It’s not important that you understand exactly

what each of these command prompts accomplishes just yet because

I’m going to completely fill you in on all of them really soon. For now,

relax and focus on just becoming familiar with the different prompts

available and all will be well!

Interfaces

To make changes to an interface, you use the

interface

command from

global configuration mode:

Switch(config)#

interface ?

Async Async interface

BVI Bridge-Group Virtual Interface

CTunnel CTunnel interface

Dialer Dialer interface

FastEthernet FastEthernet IEEE 802.3

Filter Filter interface

Filtergroup Filter Group interface

GigabitEthernet GigabitEthernet IEEE 802.3z

Group-Async Async Group interface

Lex Lex interface

Loopback Loopback interface

Null Null interface

Port-channel Ethernet Channel of interfaces

Portgroup Portgroup interface

Pos-channel POS Channel of interfaces

Tunnel Tunnel interface

Vif PGM Multicast Host interface

Virtual-Template Virtual Template interface

Virtual-TokenRing Virtual TokenRing

Vlan Catalyst Vlans

fcpa Fiber Channel

range interface range command

Switch(config)#

interface fastEthernet 0/1

Switch(config-if)#)

Did you notice that the prompt changed to

Switch(config-if)#

? This tells

you that you’re in interface configuration mode. And wouldn’t it be nice

if the prompt also gave you an indication of what interface you were

configuring? Well, at least for now we’ll have to live without the prompt

information, because it doesn’t. But it should already be clear to you that

you really need to pay attention when configuring an IOS device!

Line Commands

To configure user-mode passwords, use the

line

command. The prompt

then becomes

Switch(config-line)#

:

Switch(config)#

line ?

<0-16> First Line number

console Primary terminal line

vty Virtual terminal

Switch(config)#

line console 0

Switch(config-line)#

The

line console 0

command is a global command, and sometimes you’ll

also hear people refer to global commands as major commands. In this

example, any command typed from the

(config-line)

prompt is known

as a subcommand.

Access List Configurations

To configure a standard named access list, you’ll need to get to the

prompt

Switch(config-std-nacl)#

:

Switch#

config t

Switch(config)#

ip access-list standard Todd

Switch(config-std-nacl)#

What you see here is a typical basic standard ACL prompt. There are

various ways to configure access lists, and the prompts are only slightly

different from this particular example.

Routing Protocol Configurations

I need to point out that we don’t use routing or router protocols on 2960

switches, but we can and will use them on my 3560 switches. Here is an

example of configuring routing on a layer 3 switch:

Switch(config)#

router rip

IP routing not enabled

Switch(config)#

ip routing

Switch(config)#

router rip

Switch(config-router)#

Did you notice that the prompt changed to

Switch(config-router)#

? To

make sure you achieve the objectives specific to the Cisco exam and this

book, I’ll configure static routing, RIPv2, and RIPng. And don’t worry—

I’ll explain all of these in detail soon, in Chapter 9, “IP Routing,” and

Chapter 14, “Internet Protocol Version 6 (IPv6)”!

Defining Router Terms

Table 6.1

defines some of the terms I’ve used so far.

TABLE 6.1

Router terms

Mode

Definition

User exec mode

Limited to basic monitoring commands

Privileged exec mode

Provides access to all other router

commands

Global configuration mode Commands that affect the entire system

Specific configuration

modes

Commands that affect interfaces/processes

only

Setup mode

Interactive configuration dialog

Editing and Help Features

The Cisco advanced editing features can also help you configure your

router. If you type in a question mark (

?

) at any prompt, you’ll be given a

list of all the commands available from that prompt:

Switch#

?

Exec commands:

access-enable Create a temporary Access-List entry

access-template Create a temporary Access-List entry

archive manage archive files

cd Change current directory

clear Reset functions

clock Manage the system clock

cns CNS agents

configure Enter configuration mode

connect Open a terminal connection

copy Copy from one file to another

debug Debugging functions (see also 'undebug')

delete Delete a file

diagnostic Diagnostic commands

dir List files on a filesystem

disable Turn off privileged commands

disconnect Disconnect an existing network connection

dot1x IEEE 802.1X Exec Commands

enable Turn on privileged commands

eou EAPoUDP

erase Erase a filesystem

exit Exit from the EXEC

––More––

?

Press RETURN for another line, SPACE for another page, anything

else to quit

And if this is not enough information for you, you can press the spacebar

to get another whole page of information, or you can press Enter to go

one command at a time. You can also press Q, or any other key for that

matter, to quit and return to the prompt. Notice that I typed a question

mark (?) at the

more

prompt and it told me what my options were from

that prompt.

Here’s a shortcut: To find commands that start with a certain letter, use

the letter and the question mark with no space between them, like this:

Switch#

c?

cd clear clock cns configure

connect copy

Switch#

c

Okay, see that? By typing

c?

, I got a response listing all the commands

that start with c. Also notice that the

Switch#

c

prompt reappears after the

list of commands is displayed. This can be really helpful when you

happen to be working with long commands but you’re short on patience

and still need the next possible one. It would get old fast if you actually

had to retype the entire command every time you used a question mark!

So with that, let’s find the next command in a string by typing the first

command and then a question mark:

Switch#

clock ?

set Set the time and date

Switch#

clock set ?

hh:mm:ss Current Time

Switch#

clock set 2:34 ?

% Unrecognized command

Switch#

clock set 2:34:01 ?

<1-31> Day of the month

MONTH Month of the year

Switch#

clock set 2:34:01 21 july ?

<1993-2035> Year

Switch#

clock set 2:34:01 21 august 2013

Switch#

00:19:45: %SYS-6-CLOCKUPDATE: System clock has been updated from

00:19:45

UTC Mon Mar 1 1993 to 02:34:01 UTC Wed Aug 21 2013, configured from

console

by console.

I entered the

clock ?

command and got a list of the next possible

parameters plus what they do. Make note of the fact that you can just

keep typing a command, a space, and then a question mark until

(carriage return) is your only option left.

And if you’re typing commands and receive

Switch#

clock set 11:15:11

% Incomplete command.

no worries—that’s only telling you that the command string simply isn’t

complete quite yet. All you need to do is to press the up arrow key to

redisplay the last command entered and then continue with the

command by using your question mark.

But if you get the error

Switch(config)#

access-list 100 permit host 1.1.1.1 host 2.2.2.2

^

% Invalid input detected at '^' marker.

all is not well because it means you actually have entered a command

incorrectly. See that little caret—the

^

? It’s a very helpful tool that marks

the exact point where you blew it and made a mess.

Here’s another example of when you’ll see that caret:

Switch#

sh fastethernet 0/0

^

% Invalid input detected at '^' marker.

This command looks right, but be careful! The problem is that the full

command is

show interface fastethernet 0/0

.

Now if you receive the error

Switch#

sh cl

% Ambiguous command: "sh cl"

you’re being told that there are multiple commands that begin with the

string you entered and it’s not unique. Use the question mark to find the

exact command you need:

Switch#

sh cl?

class-map clock cluster

Case in point: There are three commands that start with

show cl

.

Table 6.2

lists the enhanced editing commands available on a Cisco

router.

TABLE 6.2

Enhanced editing commands

Command Meaning

Ctrl+A

Moves your cursor to the beginning of the line

Ctrl+E

Moves your cursor to the end of the line

Esc+B

Moves back one word

Ctrl+B

Moves back one character

Ctrl+F

Moves forward one character

Esc+F

Moves forward one word

Ctrl+D

Deletes a single character

Backspace

Deletes a single character

Ctrl+R

Redisplays a line

Ctrl+U

Erases a line

Ctrl+W

Erases a word

Ctrl+Z

Ends configuration mode and returns to EXEC

Tab

Finishes typing a command for you

Another really cool editing feature you need to know about is the

automatic scrolling of long lines. In the following example, the command

I typed reached the right margin and automatically moved 11 spaces to

the left. How do I know this? Because the dollar sign [

$

] is telling me that

the line has been scrolled to the left:

Switch#

config t

Switch(config)#

$ 100 permit ip host 192.168.10.1 192.168.10.0

0.0.0.255

You can review the router-command history with the commands shown

in

Table 6.3

.

TABLE 6.3

IOS-command history

Command

Meaning

Ctrl+P or up arrow

Shows last command entered

Ctrl+N or down

arrow

Shows previous commands entered

show history

Shows last 20 commands entered by default

show terminal

Shows terminal configurations and history buffer

size

terminal history

size

Changes buffer size (max 256)

The following example demonstrates the

show history

command as well

as how to change the history’s size. It also shows how to verify the history

with the

show terminal

command. First, use the

show history

command,

which will allow you to see the last 20 commands that were entered on

the router (even though my particular router reveals only 10 commands

because that’s all I’ve entered since rebooting it). Check it out:

Switch#

sh history

sh fastethernet 0/0

sh ru

sh cl

config t

sh history

sh flash

sh running-config

sh startup-config

sh ver

sh history

Okay—now, we’ll use the

show terminal

command to verify the terminal

history size:

Switch#

sh terminal

Line 0, Location: "", Type: ""

Length: 24 lines, Width: 80 columns

Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits

Status: PSI Enabled, Ready, Active, Ctrl-c Enabled, Automore On

0x40000

Capabilities: none

Modem state: Ready

[output cut]

Modem type is unknown.

Session limit is not set.

Time since activation: 00:17:22

Editing is enabled.

History is enabled, history size is 10.

DNS resolution in show commands is enabled

Full user help is disabled

Allowed input transports are none.

Allowed output transports are telnet.

Preferred transport is telnet.

No output characters are padded

No special data dispatching characters

When Should I Use the Cisco Editing Features?

You’ll find yourself using a couple of editing features quite often and

some not so much, if at all. Understand that Cisco didn’t make these

up; these are just old Unix commands! Even so, Ctrl+A is still a really

helpful way to negate a command.

For example, if you were to put in a long command and then decide

you didn’t want to use that command in your configuration after all,

or if it didn’t work, then you could just press your up arrow key to

show the last command entered, press Ctrl+A, type

no

and then a

space, press Enter—and poof! The command is negated. This doesn’t

work on every command, but it works on a lot of them and saves some

serious time!