Saturday, March 24, 2012

Cisco CCNA: Introduction to IOS

Cisco CCNA: Introduction to IOS


Unit 1. Router Startup



Until now, you've learned a lot of theory about networking and routers. Now it's time to transition from theory to practice. In this course, you'll begin learning the commands that are used to manage and configure your router.
In this first unit, you'll discover that the Internetwork Operating System (IOS) provides the interface between you and your Cisco router. Then you'll examine how you can access the IOS through seven command-line interfaces, each of which deals with a special aspect of router management and configuration.

After completing this unit, you should be able to:
  • Recognize which devices can access routers

  • List the three steps for system startup

  • List the seven command-line modes used to enter IOS commands

  • Identify the command prompts that differentiate the command-line modes


This unit provides information that is relevant to the following CCNA exam objectives:
  • Log in to a router in both user and privilege modes

  • Identify the main Cisco IOS software commands for router startup

  • List the commands to load Cisco IOS software from: Flash memory, a TFTP server, or ROM


Topic 1.1: Accessing the Router

*Interfacing with the IOS
The operating system for Cisco routers is the IOS (Internetwork Operating System). You enter IOS commands to start, configure, and manage your router.

*Memory for Startup
As you learned in a previous course, you can start your router from these memory locations:
  • ROM

  • NVRAM

  • Flash memory


*ROM, NVRAM, and Flash
ROM is the storage for the software that boots up the operating system. Some routers contain either a full or partial set of the Cisco IOS software image, which is the data needed by the router operating system. ROM also contains a few monitoring optionsROM is usually used for unplanned system bootups.
NVRAM is the backup storage for configuration information. NVRAM retains information when the router is not operating.
Flash memory is the storage of one or more IOS software images.

*External Locations for Startup
You can start and run your router from any of the following external locations:
  • Console port
  • Auxiliary port
  • Vty (Virtual Terminal)
  • TFTP (Trivial File Transport Protocol) server
  • NMS (Network Management Station)


*Console, Auxiliary, Vty, and TFTP
The console port connects your console directly to the router. The console is considered to be a DTE device. The auxiliary port connects the router to a modem, ISDN line, etc.
The vty actually refers to virtual terminal lines. Vty lines connect directly to a router and enable communications from another terminal on the network. Typically, vtys use the Telnet protocol to communicate through one of five available vty lines, which are labeled 0 through 4.
The TFTP server is usually a UNIX or PC workstation on the same network as the router. The NMS is usually network management software on a remote device.
If using a vty, TFTP server, or network management station, your router must also support IP.

*External Sources of Control
Similarly, these are the four external points from which you can control router access:
  • Console — the terminal that connects directly to the router
  • Telnet — a communication protocol that is typically used on vty lines
  • SNMP (Simple Network Management Protocol) — a protocol used most frequently (but not exclusively) on TCP/IP networks. SNMP communicates management information between the network management stations and other devices in the network
  • Network server — a network server, such as a TFTP or RCP server, that contains the router configuration files


Question 1

Topic 1.2: System Startup

*Ready for Router Startup
You just examined the "where" of router startup. Now you are ready for the "how."
This begins with system startup. The next few pages describe the startup steps.

*Step 1: Perform POST
Perform a power-on self-test (POST) from ROM to test the hardware.

*Step 2: Load the Image
Load the Cisco IOS software image. The software image is normally located in the router's flash memory. Some systems choose to store backup copies of the software image on another router, a workstation, or the host system.
You can boot the router system from ROM monitor mode or from pre-defined NVRAM instructions. If your router does not find a usable software image or if the loading process is interrupted, the router automatically enters ROM monitor mode.

*Step 3: Load the Config
Next, the router tries to locate and load the configuration file. The configuration file consists of router-specific data such as router properties, protocols, and interface addresses.
You can load the configuration file from NVRAM, which is the default, or a TFTP server.

*TFTP to NRAM to Setup
If the configuration file is configured for loading from the TFTP server but the router cannot find this server, the NVRAM configuration file is used. If the router cannot find any configuration file, it goes into setup mode.
When the router is in setup mode, you receive helpful prompts for entering configuration information.
Setup mode is discussed later in this course.

*Reconfigure Whenever
After the router is configured and running, you can always go back and modify the configuration files.
As an example, you can modify the configuration to change router startup to ROM, NVRAM, Flash, or a TFTP server.

Topic 1.3: Router Modes

*Interfacing with the IOS
After router startup, you use a command-line interface to execute the IOS commands that log in, configure, and manage your router.
These command-line interfaces each bring up a different set of commands.

*Every Mode Has Its Prompt
The command-line interfaces are also known as command modes. Every mode except setup is identified by its own command-line prompt.
You will see a discussion of these modes on the next few pages. For now, let's examine the command prompts and the flow from one command mode to another.

Topic 1.3.1: User EXEC Mode

*User EXEC Mode
The user EXEC mode is the first mode you see after logging in to a router. We discuss the actual login process later in this course.

*Uses for User EXEC
The basic purpose for the user EXEC mode is to provide monitoring services. User EXEC mode allows you to:
  • Connect to remote devices
  • List system information
  • Change terminal settings temporarily
  • Perform basic router testing
You cannot manage and configure routers in user EXEC mode.

*The Prompt for User EXEC
The default command-line prompt for user EXEC mode is:
Router>

Topic 1.3.2: Privileged EXEC Mode

*The Privileged EXEC Mode
To manage and configure routers, you need the other EXEC mode — the privileged EXEC mode. You can only access the privileged EXEC mode through the user EXEC mode.
The privileged EXEC mode is used for:
  • Configuration

  • Debugging

  • Reloading, which means rebooting the router when it is still operational or "hot"


*Privileges of Privileged EXEC
Privileged EXEC accepts all of the user EXEC commands, plus more. But, because it is more powerful, it is potentially destructive; therefore, privileged EXEC mode is usually password-protected.

*The Prompt for Privileged EXEC
To enter privileged EXEC mode, type the following in user EXEC mode:
Router>enable
If the mode is password protected, you are prompted for a password immediately after typing in the enable command. Passwords are discussed in depth in a later course. Once in privileged EXEC mode, you see this identifying prompt:
Router#

*Leaving Privileged for User EXEC
To leave privileged EXEC mode, type the following:
Router# disable

Question 2

Question 3

Topic 1.3.3: Global Configuration

*The Global Configuration Mode
The global configuration mode is accessible from the privileged EXEC mode. The global configuration mode:
  • Contains commands that affect the entire routing system
  • Provides access to specific configuration modes, which are generally grouped together as "other" configuration modes. These "other" modes are discussed in the next section.


*Entering Global Configuration
The command to move from privileged EXEC mode to global configuration mode follows this format:
Router#configure {terminal|memory|network}
If you type in the one-word command configure, you receive a prompt for more information, as shown here. The default answer is terminal.

*Configure Terminal by Default
You can avoid the second prompt just by adding the argument for the configuration location, like this:
Router# configure terminal

*The Prompt for Global Configuration
The global configuration mode is identified by this prompt:
Router(config)#

Topic 1.3.4: Other Configuration Modes

*From Global to Other Modes
From the global configuration mode, you can access the other configuration modes. These modes are shown here.
The prompt for these modes follows the format:
Router(config-sub_Mode_Name)#
The table on the next page shows the configuration mode name, a brief description, and the prompt.

*Other Configuration Modes
Examine the following table
Mode Description Prompt
Controller Channelized T1 lines Router(config-controller)#
Interface Specific interfaces Router(config-if)#
Subinterface Multiple virtual interfaces within one physical interface Router(config-subif)#
Line Terminal lines Router(config-line)#
Router IP routing protocols Router(config-router)#
IPX-router Novell IPX Network layer protocol Router(config-ipx-router)#
Route-map Routing tables, and source and destination data Router(config-route-map)#
Hub Hub functionality on an Ethernet interface (This mode is available on Cisco 2500 routers.) Router(config-hub)#
Map-List Map list for an ATM interface (This mode is available on Cisco 7000 routers.) Router(config-map-list)#
Map-Class QoS (Quality of Service) for an SVC (This mode is available on Cisco 7000 routers.) Router(config-map-class)#


*An Interface Example
As an example, we'll show your the interface submode, which is a submode that you will likely encounter when configuring a router. To move to the interface submode, you have to specify a specific interface, such as serial, bri (ISDN), or ethernet.
This is the general format:
Router(config)#interface interface_type interface_name

*Another Mode, Another Prompt
For example, if you want to configure a Fast Ethernet interface, you need to specify it to enter the interface submode. Once in this submode, only the commands pertinent to Fast Ethernet interfaces will be available.

Topic 1.3.5: Leaving EXEC Modes

*Exiting EXEC
To exit an EXEC mode, enter one of the following three options:
end|exit|Ctrl-Z
The option exit bumps you to whatever mode level is one-level back. In contrast, the options end and Ctrl-Z always bump you all the way back to privileged EXEC mode. In the example shown here, exit bumped you back one level (from the prompt router1(config-if) to router1(config)). The command end bumped you back to the privileged EXEC mode (router1#).

Question 4

Question 5

Topic 1.3.6: ROM Monitor

*ROM Monitor Mode
ROM Monitor mode is automatically displayed if system setup does not occur normally. For example, ROM Monitor mode appears when router bootup is interrupted or when your router cannot locate a valid Cisco IOS system image. The IOS looks for missing boot commands or the system image first in NVRAM, then in Flash memory, and finally in a network alternative.
You can force your router to stop booting by pressing the Break key sometime during the first 60 seconds of startup. After pressing Break, you will be in ROM Monitor mode.

*Some ROM Monitor Prompts
The command prompt depends on the router model. This is the prompt for Cisco 1003, 1600, 2600, 3600, 4500, 7200, and 7500 routers:
rommon>
*Other ROM Monitor Prompts
On all other routers, the command prompt is simply the left-angle bracket:
>

*From ROM to User EXEC
To move from the ROM Monitor mode to the user EXEC mode, use this command:
rommon> continue

Topic 1.3.7: RXBoot

*RXBoot Mode
RXBoot mode is used when your router cannot locate a valid Cisco IOS system software image in Flash memory. A copy of the Cisco IOS software image should reside in the read-only Flash memory.
If the router cannot find a valid image, you can modify the Configuration register, which contains the information for loading a whole or partial system image and where the image can be found. We will discuss the Configuration register later in this course.

*The Prompt for RXBoot
The command prompt for RXBoot mode is:
Router<boot>

Question 6

Question 7

Topic 1.3.8: Setup

*Setup Mode
Setup mode provides interactive questions that guide users who are new to IOS configuration. Unlike the other command modes, the question dialog replaces command prompts; therefore, setup does not have an identifiable command prompt.

*Reasons for Setup
As you learned in the beginning of this unit, you can enter setup mode automatically if:
  • The configuration file on the TFTP server cannot be found.
  • The NVRAM configuration file is either lost or corrupted.
  • The router cannot find any configuration file.

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]:
...
*From Privileged EXEC to Setup
You can access setup mode from the privileged EXEC mode by typing the following:
Router#setup
In a later unit we will discuss how to perform a first-time configuration in setup mode.


* Exercise 1
Try identifying the command modes that are used to configure and manage routers.


Examine the following table
Step Action
1 List the seven command modes for configuring and managing routers. Include all of the "other" configuration modes that are used for specific configurations.
2 Identify the primary purpose of each mode.
3 Identify the command prompt that distinguishes each mode.


Topic 1.4: Unit 1 Summary

Even learning Cisco IOS commands requires additional background knowledge. In this unit, you examined the command-line interface modes that allow you to interact with the Cisco IOS. While looking at these modes, you did learn a few commands, such as the commands that allow you to navigate from one command-line mode to another.
In the next unit, you'll learn how the setup mode guides you through the initial configuration of your router.

Unit 2. Router Startup in Setup Mode



A router needs a configuration file, which consists of router-specific data, in order to work. A startup-config file is stored on the router and remains in memory even when the router is turned off. When the router is running, it creates a running-config file, which is based on the startup-config file.
If the router cannot find any startup-config file from NVRAM or the TFTP server, it goes into setup mode, at which time you are prompted to enter the configuration information.
In this unit you'll use setup mode to build the initial router configuration.

After completing this unit, you should be able to:
  • Enter and exit setup mode

  • List the information that setup mode needs during an initial configuration


This unit provides information that is relevant to the following CCNA exam objective:
  • Check an initial configuration using the setup command


Topic 2.1: Setup Overview

*Setup before and after Startup
Setup mode is used most often during the initial router startup. However; it can also be used in a production environment, such as when someone types a destructive command like erase startup-config and you're unable to reboot your router normally.

*Almost an IOS Interview
Setup mode walks you through configuration with interactive prompts.
The exact context of these prompts directly depends upon your input. For example, if you want to configure a Frame Relay interface, you won't be prompted for a PPP configuration.
Setup prompts you for global configuration parameters first, and then interface parameters.

*Entering Setup
You can access setup mode from the privileged EXEC mode by typing:
Router#setup
In addition, setup mode automatically appears if the router cannot find any startup-config file, or if the NVRAM startup-config file is corrupted.

*Setup Responses
For some responses, setup lets you press Enter to accept the default. But, if your response affects subsequent prompts or the permanent configuration, it requires you to type out your response in full, such as: yes or no. If you need help, type a ? at the prompt.

*Starting Over
If, sometime during the setup configuration, you decide that you want to start over, all you need to do is press Ctrl-c, and then re-enter the setup command.  

Question 8

Topic 2.2: A Setup Example

*A Setup Configuration
In this section, we'll show you an actual initial configuration using setup. Our example is a Fast Ethernet LAN, before it is connected to a WAN ATM. Our code is taken from a log file recorded at the console.

Note: Remember — the actual setup dialog may differ from one IOS release to another.


*System Configuration Dialog
This is how the System Configuration Dialog begins.
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

Topic 2.2.1: Configuring Host Name and Passwords

*Global Parameters First
At this point during the setup process, you will be prompted to supply the following:
  • Router host name
  • Enable secret password
  • Enable password
  • Virtual terminal password
The basics of the configuration input will be explained in a later course; our intention now is to introduce you to setup.

*The Router Name
In the output shown, we have entered some input, first for the host name. After configuration is finished, the host name appears in the router prompt.
Configuring global parameters:
Enter host name [Router]: router1

*The Enable Secret Password
Next come the passwords. First, you have the enable secret password, which takes you from user to privileged EXEC mode.
The enable secret is a password used to protect access to
     privileged EXEC and configuration modes. This password, after
     entered, becomes encrypted in the configuration.
     Enter enable secret: enableSecretPassword

*The Enable Password
The enable password is used less often, such as when an enable secret password is not provided.
The enable password is used when you do not specify an
     enable secret password, with some older software versions, and
     some boot images.
     Enter enable password: enablePassword

*The Vty Password
Finally, you are prompted to enter the password that allows a vty user, who commonly uses Telnet, to log into the router in the user EXEC mode.
The virtual terminal password is used to protect
     access to the router over a network interface.
     Enter virtual terminal password: vtyPassword

Topic 2.2.2: Configuring SNMP

*SNMP: Public or Private?
Next, setup issues prompts about configuring Simple Network Management Protocol (SNMP). SNMP manages network devices and configurations, among other tasks, on TCP/IP networks.
If you aren't sure what to enter, it's usually safe to choose the defaults, which are shown inside the brackets.
Configure SNMP Network Management? [yes]:
    Community string [public]:

*Dialog for Older IOS Versions
Here are the SNMP prompts for some older IOS versions.
Enter yes or press Return to accept SNMP management; enter no to refuse it.
     Configure System Management? [yes/no]:
     Configure SNMP Network Management? [yes]:

Topic 2.2.3: Configuring the Interface

*Interface Parameters Follow Global Parameters
Next, setup provides you with an interface summary. So far, we have just the Fast Ethernet interface available for setup.
Obviously, your interface and IOS version influences the actual content of the output.
Current interface summary
Any interface listed with OK? value "NO" does not have a valid configuration
Interface          IP-Address  OK? Method  Status      Protocol
FastEthernet0/0    unassigned  NO  unset   up          down

*Configuration Needed
The dialog states that interfaces showing a NO in the OK? column need to be configured.
The interface description describes the interface type, router chassis slot number, and the unit number. Therefore, for the second entry shown (Fast Ethernet0/1), Fast Ethernet is the interface type, 0 is the slot number, and 1 is the unit number.
Any interface listed with OK? value "NO" does not have a valid configuration
Interface         IP-Address   OK?  Method  Status  Protocol
Fast Ethernet0/0  unassigned   NO   un set  up      up
Fast Ethernet0/1  unassigned   NO   un set  up      up

*IP Routing
If you are configuring IP routing, which is a common configuration, you can use most of the default values.
Enter interface name used to connect to the
management network from the above interface summary: fastethernet0/0
Configuring interface FastEthernet0/0:
  Use the 100 Base-TX (RJ-45) connector? [yes]:
  Operate in full-duplex mode? [no]: yes
  Configure IP on this interface? [yes]:
    IP address for this interface: 192.168.1.27
    Subnet mask for this interface [255.255.255.0] :
    Class C network is 192.168.1.0, 24 subnet bits; mask is /24

*IP Dialog in Older IOS Versions
In some older IOS versions, you have more prompts for IP routing. For example, you are prompted to specify an interior routing protocol such as Interior Gateway Routing Protocol (IGRP) or Routing Information Protocol (RIP).
Here is the setup dialog for IP routing with IGRP, the default. CLNS, mentioned in the last line, is the abbreviation for Connectionless Network Service. CLNS is a Network layer service that can transmit data without establishing a circuit first.
Configure IP? [yes]:
     Configure IGRP routing? [yes]:
     Your IGRP autonomous system number [1]:
     Configure CLNS? [no]:

Topic 2.2.4: Viewing the Configuration

*Configuration Summary
At this point, setup summarizes what you've configured.
The following configuration command script was created:
hostname router1
enable secret 5 $1$DQq7$GXmqqubDE/5i0nupMKcfo/
enable password enablePassword
line vty 0 4
password vtyPassword
snmp-server community public
!
no ip routing
!
interface FastEthernet0/0
no shutdown
media-type 100BaseX
full-duplex
ip address 192.168.1.27 255.255.255.0
!
end

Topic 2.2.5: Saving the Configuration

*Save or Not Save
Now, the final set of prompts. You can save your configuration to NVRAM, or return to privileged EXEC mode or setup. There is no default for this set of prompts.
[0] Go to the IOS command prompt without saving this config.
[1] Return back to the setup without saving this config.
[2] Save this configuration to nvram and exit.
Enter your selection [2]:

*Saving to NVRAM
In our example, we entered a 2, which saves our configuration to NVRAM for permanent storage.
Although setup provides enough simple configuration to make your router ready to use, it is advisable to use the configuration mode for more in-depth configuring.
[0] Go to the IOS command prompt without saving this config.
[1] Return back to the setup without saving this config.
[2] Save this configuration to nvram and exit.
Enter your selection [2]: 2
Building configuration...
Use the enabled mode 'configure' command to modify this configuration.
Press RETURN to get started!

*Exiting Setup
Before exiting, setup displays these run-time statistics:
00:00:06: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
00:00:07: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, chang
ed state to up
00:00:14: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, chang
ed state to down
00:15:31: %IP-5-WEBINST_KILL: Terminating DNS process
00:15:43: %SYS-5-RESTART: System restarted --
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-I-M), Version 12.0(3)T3,  RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Thu 11-May-99 12:24 by esoa
00:15:45: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up5


* Exercise 1
Try listing the configuration parameters that you'll need to configure your router in setup mode.

Examine the following table
Step Action
1 You've seen a sample configuration in setup mode. Regardless of what interfaces you may be using at your own site, there are some basic configuration parameters that are needed for interfaces. List as many of these parameters as you can.
2 Now try to identify the configuration parameters needed specifically for your site.


Topic 2.3: Unit 2 Summary

In this unit, you learned how to build an initial router configuration in setup mode. Once your router is in production, though, you will typically use the privileged EXEC mode. In fact, if you want to perform a complex configuration, you must use the privileged EXEC mode.
In the next unit, you'll learn more about finding and using EXEC mode commands.

Unit 3. EXEC Mode Commands



When managing and configuring your Cisco IOS router, you spend most of your time in the user and privileged EXEC modes.
In this unit, you'll learn some shortcuts that you can use. You'll explore context-sensitive help, which displays the commands available in the current command-line mode. You'll also examine the enhanced editing commands.
And last, but not least, you'll take a brief look at a few commands that are useful for managing and configuring your router.

After completing this unit, you should be able to:
  • Log in to a router

  • Access context-sensitive help for command words and syntax

  • Apply enhanced editing commands for moving the cursor through one command or through the buffer of previous commands

  • Explain how the commands no, ping, and exec-timeout function


This unit provides information that is relevant to the following CCNA exam objectives:
  • Log in to a router in both user and privilege modes

  • Use the context-sensitive help facility

  • Use the command history and editing features

  • Control router passwords, identification, and banner

  • Identify the main Cisco IOS software commands for router startup


Topic 3.1: Login Commands

*A Little about the Login
Our first order of business is to talk about the login process. The login process varies slightly, depending on the password configuration. Some network administrators require a login password for the virtual terminal lines but not for the console. If no password is needed, then all you need to do is press Enter to bring up user EXEC prompt.
For example, here is a typical console login that does not require a password.

*Logging In with a Password
A Telnet login is often configured so that it requires a password. Here is an example of a Telnet login that is prompting for a password.

*Moving Past the Login
If the login is successful, then you will see the prompt for the user EXEC mode.

*Timing Out
If you do not type any input for a specified time interval, you are logged out. By default, this time interval is 10 minutes. Of course, like most router parameters, the time interval can be reconfigured.

*Logging Out
As you already know, in order to continue forward to privileged EXEC mode, you can type enable to enter and disable to exit.
To exit the user EXEC mode and to log out of the router IOS, type exit or logout, as shown here.

Topic 3.2: Context-Sensitive Help

*Help Is Always Available
The user and privileged EXEC modes offer a helpful utility called context-sensitive help. You can use a combination of abbreviations and the question mark (?) symbol to call up commands and command syntax.

*Scrolling with More
If the display area cannot display the full output, the word -- More -- appears at the bottom of the screen.
To display just the next line of output, you need to press Enter; to display the next full page of output, you need to press the spacebar.
If you press a key besides Enter or the spacebar, the ? command will cease execution and you will return to the EXEC mode prompt.

*Two Kinds of Help
Context-sensitive help actually consists of two types of help: word help and command syntax help. The placement of the question mark determines what type of help you are requesting.

*Word Help
Word help provides a list of commands that begin with a specified combination of letters.
As shown here, the command lo? calls up a list of commands that begin with lo. Notice that the question mark immediately follows the letters. Then, notice the output. Also notice that the router redisplays what you have typed in, without the question mark, so that you can examine the output and finish typing the desired command.

*Command Syntax Help
Command syntax help displays the arguments and keywords that can be used with a command that you specify.
For example, ping ? displays the arguments for the command ping. Notice the space preceding the question mark, and then notice that the arguments are displayed, as shown here.

*No Arguments Needed
The <cr> in the output means that you can just type the command without any arguments and then press Enter to execute the command.

*Help Is Mode-Sensitive
The command for which you are requesting help must be available in the current mode. As shown here, you cannot request context-sensitive help for a configuration command while in user EXEC mode, because all configuration is done in the privileged EXEC mode.

*IOS Eliminates Some Typing
If you type in enough of a command so it is unique, and therefore recognizable to the router IOS, the IOS will act upon that command. This is true in any of the command-line modes and is not restricted to context-sensitive help.
For example, if you type config t, the router IOS knows you want the command configure terminal.
If you type in config, the router IOS will prompt you to decide whether you want to configure from memory, the network, or the terminal.

Question 9

Topic 3.3: EXEC Mode Commands

*Looking at Individual Modes
As you just discovered, you type just a ? after the prompt to display word help. Word help displays the commands available in the current mode.
In the next sections, we will list the available commands for the user, privileged EXEC, and global configuration modes.

Topic 3.3.1: User EXEC Mode

*User EXEC Commands
Here are the user EXEC commands. We are showing the commands just to give you an idea of the types and quantity of commands available in the user EXEC.
This list may vary in different IOS versions.
Router1> ?
Exec commands:
 connect          Open a terminal connection
 disconnect       Disconnect an existing telnet session
 enable           Turn on privileged commands
 exit             Exit from the EXEC
 help             Description of the interactive help system
 lock             Lock the terminal
 login            Log in as a particular user
 logout           Exit from the EXEC
 name-connection  Name an existing telnet connection
 ping             Send echo messages
 resume           Resume an active telnet connection
 show             Show running system information
 systat           Display information about terminal lines
 telnet           Open a telnet connection
 terminal         Set terminal line parameters
 where            List active telnet connections

Topic 3.3.2: Privileged EXEC Mode

*Privileged EXEC Commands
Here is the list of commands available at the privileged EXEC prompt. The list may vary in different IOS versions.
Router1# ?
Exec commands:
 bfe              For manual emergency modes setting
 clear            Reset functions
 clock            Manage the system clock
 configure        Enter configuration mode
 connect          Open a terminal connection
 copy             Copy a config file to or from a tftp server
 debug            Debugging functions
 disable          Turn off privileged commands
 disconnect       Disconnect an existing telnet session
 enable           Turn on privileged commands
 exit             Exit from the EXEC
 help             Description of the interactive help system
 llc2             Execute llc2 tests
 lock             Lock the terminal
 login            Log in as a particular user
 logout           Exit from the EXEC
 name-connection  Name an existing telnet connection
 ping             Send echo messages
 reload           Halt and perform a cold restart
 resume           Resume an active telnet connection
 send             Send a message to other tty lines
 setup            Run the SETUP command facility
 show             Show running system information
 systat           Display information about terminal lines
 telnet           Open a telnet connection
 terminal         Set terminal line parameters
 test             Test subsystems, memory, and interfaces
 trace            Trace route to destination
 where            List active telnet connections
 which-route      Do route table lookup and display results
 write            Write running configuration to memory, network, or terminal

Topic 3.4: Enhanced Editing Commands

*Moving from Context-Sensitive Help to Editing Commands
Enhanced editing commands are keyboard commands that are especially useful for scrolling horizontally (i.e., left and right) through long commands.
Here are the enhanced editing commands:
  • Ctrl-a — Move to the beginning of the command line
  • Ctrl-e — Move to the end of the command line
  • Ctrl-f (or right arrow) — Move forward one character
  • Ctrl-b (or left arrow) — Move back one character
  • Esc-b — Move to the beginning of the previous word
  • Esc-f — Move forward one word


*Scrolling Horizontally
The enhanced editing commands are especially useful for long commands.
As you use the editing commands to scroll horizontally to the right, the beginning of the command disappears from the display.

*Scrolling Horizontally in Long Commands
If you scroll past the beginning of a long command line, a dollar sign ($) appears to signify that the beginning of the line is not displayed.

*Enhanced by Default
If you are using a recent version of IOS, enhanced editing is enabled by default at router startup.
Sometimes, however, you may not want enhanced editing. As an example, enhanced editing may not be compatible with scripts that you have written.

*Disable for a Session
Enhanced editing can be disabled for the current session with the command terminal no editing. As shown here, the Ctrl-a is not recognized after enhanced editing is disabled.
Enhanced editing for a session can be re-enabled with the command terminal editing. As you can see, once editing is re-enabled, the cursor moves back to the beginning of the line.

Topic 3.5: Command Shortcut with the Tab Key

*Using Tab in Addition to Enter
You can complete a command by entering some portion of a command and pressing the Tab key. You must enter enough of the command so that it is unique and recognizable to the IOS. If there is more than one possible command that fits your input, you receive an error message, which is usually a beep.
For example, you can type the following command, which ends in a Tab:
sh run Tab
The command sho run appears again but does not execute, as shown by the cursor position at the end of the line.

*Why Use Tab?
The Tab key is only an option and not a necessity, especially since the IOS can interpret abbreviated commands and prompt you for more input as needed.
Some network administrators like using the Tab key for critical commands or for commands that affect remote routers. By using the Tab key, the entire command is presented to you before you press Enter to execute it.

Topic 3.6: Commands for Recalling the Command Buffer

*Scrolling Up and Down
The enhanced editing commands in the last section help you navigate horizontally through one command line. That's useful, but so is navigating up and down through previously executed commands, which are stored in the command buffer.
To see the commands stored in the buffer type this:
show history
The previous commands are listed in the order that they were executed.

*A Default of Ten
By default, the IOS saves the previous 10 commands for the current session, although it can save as many as 256 commands.
You can change the number of commands in the history buffer with this command:
terminal history size n
The command shown here saves the previous 30 commands.

*Scrolling by One
These two keyboard commands function very much like the show history command. The basic difference is that these shortcut commands recall previous commands one at a time:
  • Ctrl-p (or Up arrow) — Moves backward in the command history from newer to older commands. You can use this repeatedly to scroll through previous commands, beginning with the most recent command and proceeding backward to progressively older commands.

  • Ctrl-n (or Down arrow) – Moves forward in the command history from older to newer commands. You can use this repeatedly to scroll through previous commands, beginning with the command last recalled by Ctrl-p and proceeding forward to progressively newer commands.


Question 10

Question 11

Topic 3.7: Other Useful Commands

*Three Commands to Remember
As you become familiar with your router and your network, you'll rely on certain commands. Here are three that you'll probably need:
  • no
  • ping
  • exec-timeout
These commands can be used in user EXEC and privileged EXEC modes. Let's take a look at a short introduction to each of these commands.

Topic 3.7.1: Using no

*The no Command
no is a keyword that precedes a command that you want to undo. The keyword no disables or reverses a function. This is especially useful for default configurations that you want to disable. Because it changes configuration parameters, no does not work in user EXEC mode.
For example, if you wanted to disable debugging in privileged EXEC mode, this is what you would type:
no debug

*The no editing Command
Another example is the no editing command. This command, which is found in the line submode of global configuration, disables enhanced editing on a long-term basis.
But, as you know, the editing option is different than most commands in that you can disable it permanently or just for the current session. If you use terminal no editing in user EXEC mode, editing is disabled just for the current session.

Topic 3.7.2: Using ping

*The ping Command
The second useful command is ping (Packet Internet Groper). Routers rely on this command to test whether a network device can be reached. It is commonly used to test Internet connections.
As shown here, ping works in user and privileged EXEC mode, although privileged EXEC mode offers more options.

ping Responses
The following symbols represent ping responses. As shown here, one ping can have a mixed response:
  • !
  • Successful receipt of an echo reply
  • .
  • Timed out waiting for a reply
  • U
  • Destination unreachable
  • C
  • Congestion-experienced packet
  • I
  • Ping interrupted
  • ?
  • Packet type unknown
  • &
  • Packet TTL exceeded


*A ping Example
In the example shown here, the .!!!! sequence indicates that you sent 5 ping messages. The first message timed out and was not successful in reaching its destination. The period (.) represents the timed-out message. The four exclamation points (!!!!) represent the four successful pings.

Topic 3.7.3: Using exec-timeout

*The exec-timeout
Now for the third useful command. If you are a system administrator responsible for network security, you may need a command that allows the user and privileged EXEC modes to time out after a specified time.
The default time interval is 10 minutes. The show running-config output shown here indicates that the exec-timeout has been modified for both the console and vty lines.

*Use the Line Submode
To change the default time interval to n number of minutes, follow this format:
exec-timeout minutes [seconds]
For example, if you want the console to time out in five minutes, begin by entering the global configuration mode, and then entering the line mode, as shown here.

*Combining no and exec-timeout
To remove the timeout period, type the following:
no exec-timeout    or    exec-timeout 0

Question 12

Question 13


* Exercise 1
Try using context-sensitive help to differentiate the commands available in different command-line modes of the Cisco IOS.

Examine the following table
Step Action
1 Log in to your router IOS. Remain in user EXEC mode.
If you do not have access to a router, simulate this exercise on paper by using the list of commands from this unit or Cisco's Web site.
2 Use the ? option of context-sensitive help to bring up the list of commands.
3 Choose at least three commands, and use the command syntax help to show the arguments for these commands. Include no and ping as two of the three commands.
4 Repeat steps 2 and 3 for the privileged EXEC mode.
5 Repeat steps 2 and 3 for the global configuration mode.
6 Repeat steps 2 and 3 for the line submode of the global configuration mode.
7 Compare the availability of your three selected commands in each mode. Also, compare the available arguments for each command in each mode.
8 Log out of your router IOS.


Topic 3.8: Unit 3 Summary

As you have discovered, the IOS software provides tools that simplify router interaction. If you're new to the command language, the context-sensitive help can supply much of the command information that you will need. If you've already mastered the use of commands, the editing keyboard commands help you work more efficiently.
In the next unit, you'll learn the commands that let you check the status of your router.

Unit 4. Router Status



Suppose you're looking at a router in operation, and you want to know more about it: you may just be curious, or maybe you're trying to debug your system. A wealth of information can be displayed using the IOS show commands.
In this unit we'll focus on the commands that show you the router's status.

After completing this unit, you should be able to:
  • List the show commands that display router status

  • Compare the output displayed by each command

  • Recognize when to use these commands


This unit provides information that is relevant to the following CCNA exam objectives:
  • Examine router elements

  • Identify the main Cisco IOS software commands for router startup


Topic 4.1: Introduction

*Two Modes for Showing
Because they are so vital to the monitoring of router operation, show commands are available in the user and privileged EXEC modes.

*Showing Nine, without an Argument
Many show commands take arguments. However, we will show you the arguments but only discuss each command as it executes without arguments (with one exception — show ip route). In this unit, we will discuss each of the following show commands:
  • show flash
  • show interfaces
  • show ip route
  • show memory
  • show processes
  • show protocols
  • show running-config — also known as write term on Cisco IOS Release 10.2 and earlier
  • show startup-config — also known as show config on Cisco IOS Release 10.2 and earlier
  • show version


Topic 4.2: show flash

show flash
The show flash command displays information about the Flash memory, which stores the IOS software. The Flash can save multiple files containing different versions of the IOS. As shown here, context-sensitive help displays the possible arguments.

*What show flash Displays
The show flash command, without arguments, displays
  • Number of files in Flash memory
  • File length of each file
  • File name(s) currently in the Flash memory
  • Byte statistics of the Flash memory usage


*The System Image File
The name of the file stored in the Flash memory tells you more about the IOS software. In this example, c2600 is the router platform, 120-3 tells you that the IOS version is 12.0-3.

*Another System Image File
Here is an example of another Flash file name:
  • c2500 is the platform

  • js indicates that it is an enterprise image with extended capabilities

  • 1 indicates that the file can be relocated and is not compressed

  • 112-6 indicates that it is IOS version 11.2-6

  • bin indicates that it is a binary, executable file

c2500-js-1.112-6.bin

Topic 4.3: show interfaces

show interfaces
The show interfaces command displays real-time statistics about each interface that has been configured on a router.

*Output for show interfaces
The next two pages show examples of typical show interfaces output. Other interface-specific statistics include the following:
  • State of an interface
  • Maximum transmission units
  • MAC address for the LAN card (e.g., Ethernet, Token Ring, or FDDI interface)
  • Encapsulation type
  • Number of packets received
  • Number of input and output packet errors
  • Number of collisions detected (i.e., on an Ethernet interface)
Incidentally, a runt is a packet that is not legal because it is too small; a giant is a packet that is too big. In addition, MTU stands for maximum transmission unit, BW for bandwidth, DLY for delay.

*Why Use show interfaces?
There are several advantages to the show interfaces command:
  • It shows the activity of a specific interface, which is invaluable in determining whether the interface is functioning correctly.

  • It can show if any interface configuration parameters have been changed.


Topic 4.4: show ip route

show ip route
This command is really show ip, with route as an argument. This command is used often with the argument, especially because show ip alone has more than forty arguments.

*What show ip route Displays
Generally, show ip route displays the protocol-independent entries contained in the routing table, such as the following:
  • Protocol used to derive route — such as IGRP or RIP
  • Type of route — such as IA for the OSPF inter-area route
  • Address of specified remote network
  • Address of next router on the way to the specified remote network
  • Administrative distance of the information source and router metric — presented as numbers inside brackets (i.e., [Distance/metric])
  • Time of last router update
  • Interface to specified remote network


*An Example of show ip route Output
This is a typical output for show ip route.

Question 14

Question 15

Topic 4.5: show memory

show memory
The show memory command shows memory statistics for a particular router. An example of a memory statistic is the memory free pool.


*Typical show memory Output
Here is the typical show memory output. Output covers these statistics:
  • Memory type — such as io, multibus, sram, processor
  • Head — hexadecimal address of the head of the memory allocation chain
  • Total — total bytes, both used and free
  • Used — bytes of memory used
  • Free — bytes of memory not used
  • Lowest —smallest number of free bytes since router was last booted
  • Largest — number of bytes in the largest available free block


Topic 4.6: show processes

show processes
The command show processes displays the status of active processes. As before, here are the arguments that can be used with this command.


show processes Produces Prolific Output
The output for this command is quite extensive, and scrolls through many screens. The next page shows a table that describes the output parameters.

*Output for show processes
Examine the following table
Output Parameter Description
CPU utilization for five seconds Percent CPU utilization for the last five seconds/percent of CPU time at the interrupt level
One minute Percent CPU utilization for the last minute
Five minutes Percent CPU utilization for the last five minutes
PID Process ID
Q Process queue priority, which is listed as H (high), M (medium), L (low)
Ty Scheduler test, which can have one of these values: * (currently running), E (waiting for an event), S (ready to run, voluntarily relinquished processor), rd (ready to run, wakeup conditions have occurred), we (waiting for an event), sa (sleeping until an absolute time), si (sleeping for a time interval), sp (sleeping for a time interval (alternate call), st (sleeping until a timer expires), hg (hung; the process will never execute again), and xx (dead; process has terminated, but not yet been deleted)
PC Current program counter
Runtime CPU time, in milliseconds, that has been used by the process
Invoked Number of times the process has been invoked
uSecs CPU time, in microseconds, for each process invocation
Stacks Low water mark/total stack space available, in bytes
TTY Terminal that is controlling the process
Process Process name
5Sec CPU usage by task for the last five seconds
1Min CPU utilization by task for the last minute
5Min CPU utilization by task for the last 5 minutes


Topic 4.7: show protocols

show protocols
The command show protocols displays the global and interface-specific status of all Network layer protocols that have been configured on the router.
Global status includes potential traffic the router could pass. Interface-specific status includes configuration parameters such as protocol addresses.

*Output for show protocols
Here is an example of typical show protocols output.

Topic 4.8: show running-config

show running-config
The command show running-config replaces write term, which was used in versions 10.2 and earlier. show running-config displays the configuration parameters that are active. Active parameters are those that are currently running in terminal memory. For example, parameters include the IOS version, router hostname, and router IP address.

*Output for show running-config
The output is shown here and on the next page. You can differentiate running configuration from startup configuration parameters because the screen output says Current configuration...

Topic 4.9: show startup-config

show startup-config
The show startup-config command displays the backup configuration file. The backup configuration file contains such parameters as IOS version, router hostname, passwords, and NVRAM usage. These are the parameters that the router uses on restarts.
There are no arguments for this command.

*Output for show startup-config
Here is the first portion of the show startup-config output. The remainder of the output is shown on the next page.

Topic 4.10: show version

show version
In the event that you need to call Cisco customer support, you can use the show version command to obtain the IOS version and revision number. The revision number is the number in parentheses that appears immediately after the version number.
If one or more routers are problematic, use this command to ascertain whether they share a specific parameter.

*What show version Displays
The command show version displays the following:
  • IOS version that is running

  • Revision number of the IOS version

  • Length of time the system has been up and running

  • Name and origin of the system image file (boot file)

  • Names and location of configuration files
On some versions, the output may also show how the IOS is being loaded, such as a boot from the TFTP server.

*Sample show version Output
Here is typical show version output.

Question 16

Question 17

Question 18


* Exercise 1
Try using the show commands in different command-line modes.

Examine the following table
Step Action
1 Log into your router. Remain in the user EXEC mode.
2 Type the show commands in the user EXEC mode.
3 Enter the privileged EXEC mode. Once again, type the show commands.
4 Do this with the global configuration and any other configuration modes to which you have access.
5 Compare the output for the commands in each mode.


Topic 4.11: Unit 4 Summary

In this unit, you discovered how to use the show commands to display router status.
You will apply two of the show commands that you just learned about — show running-config and show startup-config — in the next unit, where you will learn how to load configuration files onto your router.

Unit 5. Loading Configuration Files



You've studied the show commands that return router status. In this unit, you'll apply two of those commands.
In addition, you'll learn the differences between running-config files and startup-config files, and how to load them onto your router. You will also learn how to reverse configuration changes that you have made.

After completing this unit, you should be able to:
  • List the sources for configuration files

  • Explain the commands for loading configuration files

  • Describe how the Cisco software image can affect configuration files

  • Differentiate between noninvasive, invasive, and last resort changes

  • Compare the commands for undoing configuration changes


This unit provides information that is relevant to the following CCNA exam objectives:
  • Manage configuration files from the privilege EXEC mode

  • List the commands to load Cisco IOS software from: Flash memory, a TFTP server, or ROM

  • Prepare to backup, upgrade, and load a backup Cisco IOS software image


Topic 5.1: Preparing for Loading

*NVRAM and RAM Files
The router obtains its operating parameters from configuration files. Generally, the configuration file that is stored in NVRAM is called the startup-config. When the router is started, this file is placed into RAM. The RAM configuration file is called the running-config.

*Running-Config is Temporary
Any configuration changes that you make during router runtime are made in the running-config only; you have to copy the running-config to the startup-config if you want to keep these runtime changes.
If you do not make any runtime changes, the running-config file remains identical to the startup-config file.

*Loading Is a Privileged Operation
For security reasons, not everyone can load configuration files. Therefore, you must enter the privileged EXEC mode. For a portion of the loading you must proceed to the global configuration mode.
Just as a reminder, here is the sequence of commands that lead you from the user EXEC to the global configuration mode.

*File Storage
You have the option of loading your configuration files into RAM from these sources:
  • Console or terminal

  • NVRAM

  • TFTP server


*System Image Files
The source (e.g., console, NVRAM, TFTP server) is not the only variable in loading configuration files. The Cisco IOS version is another. The commands for configuration vary from IOS releases 10.2 and earlier, to IOS releases 10.3 and later.
We will cover the different commands for each source, as well as the earlier and later IOS releases.

*Comparing Older and Newer
Before we begin, we'll show you a table of configuration commands that have changed. We will discuss some of the configuration command changes in this unit.
Examine the following table
Command for IOS Release 10.2 and earlier Same Command for IOS Release 10.3 and later
configure network copy rcp running-config (for an rcp server)
copy tftp running-config (for a TFTP server)
configure overwrite-network copy rcp startup-config (for an rcp server)
copy tftp startup-config (for a TFTP server)
show configuration show startup-config
write erase erase startup-config
write memory copy running-config startup-config
write network copy running-config rcp (for an rcp server)
copy running-config tftp (for a TFTP server)
write terminal show running-config


Topic 5.1.1: Loading from Releases 10.2 and Earlier

*Configuring from Console
Here are the commands for IOS releases 10.2 and earlier for configuring from the terminal or console.
Notice that the prompt tells us we are in privileged EXEC mode.
Router#configure terminal
*Configuring from NVRAM
If you want to use the configuration stored in NVRAM, type this.
Router#configure terminal

*Configuring without RAM
You can load a file into NVRAM, without affecting the RAM file or the running-config file. To do this, type the command shown here.
When using this command, you have to load a file that is not too big for NVRAM.
Router#configure overwrite-network

*Showing the Startup-Config
For IOS 10.2 and earlier releases, you type this to see the startup-config file parameters. You can shorten this command to show config.
Router#show configuration
*Showing the Running-Config
You type this to see the running-config file parameters. You can shorten this command to write term.
Router#show configuration

*Saving from Running-Config to Startup-Config
If you have made changes to the running-config, and have looked at it to verify its accuracy, then you can copy the configuration to the startup file with this command.
Router#write memory

Question 19

Question 20

Topic 5.1.2: Loading Earlier Releases from a TFTP Server

*Loading from the TFTP Server
The TFTP server is useful when you are managing several routers. You can store a configuration file on the TFTP server and download it to all of the routers.
By doing this, you can feel more confident that all of the routers are using the same configuration file, and, if changes are needed, you can modify just one configuration file on the server instead of every file on every router.
Loading a startup-config file from the TFTP server into RAM involves a series of commands, which are discussed on the next few pages.

*Step 1: Specify Source
 First, you enter the command shown here, which can be typed as config net. This commands puts you in the global configuration mode.
Router#configure network

*Step 2: Load Host or Network Config
At this point you are prompted to load either the host configuration file or the network configuration file.
The host configuration file, which is router-specific, is the default. The network configuration file is network-specific, which means it applies to all routers and servers in the network.
Router1#configure network
Host or network configuration file [host]?

*Step 3: Enter IP
Next, you are prompted to enter the IP address of the remote host. The configuration file resides on this remote host. The default is 255.255.255.255.
Router1#configure network
Host or network configuration file [host]?
IP address of remote host [255.255.255.255]? 204.101.202.245

*Step 4: Name and Confirm
Finally, you are prompted to enter the name of the configuration file, and then to confirm that name. If you do not enter a file name, the default name router-confg is used.
Router1#configure network
Host or network configuration file [host]?
IP address of remote host [255.255.255.255]? 204.101.202.245
Name of configuration file [router-confg]?
Configure using router-confg from 204.101.202.245? [confirm] y
Booting router-confg from 204.101.202.245:!! [OK - 874/16000 bytes]

*Saving Running-Config to NVRAM
If you make changes to your running-config and you want to save them for future use, then you can use the command shown to copy these changes to your startup-config.
Router#write memory
*Saving Running-Config to TFTP
If you want to save the running-config changes back to the TFTP server startup file, use this command.
Router#write memory

Question 21

Topic 5.1.3: Loading from Releases 10.3 and Later

*Configuring from the Terminal or Console
Now we're going to repeat the loading commands, only this time we will be discussing the commands for IOS releases 10.3 and later.
If loading from the terminal or console, use this command.
Router#configure terminal

*Loading Running-Config into RAM
If you want to copy the TFTP running-config file directly into RAM, type the command shown below.
This does not change the startup-config file that is stored in NVRAM.
Router#copy tftp running-config

*Loading Startup-Config into RAM
If you want to copy the TFTP startup-config file into NVRAM for subsequent loading into RAM, type the command shown below.
This does change the startup-config file that is stored in NVRAM.
Router#copy tftp startup-config

*Replacing Running-Config with Startup-Config
If you want to restore the backup configuration in NVRAM to the running configuration in RAM, type this:
Router#copy startup-config running-config

*Replacing Startup-Config with Running-Config
If you make changes to your running config and you want to save these changes, use this command:
Router#copy running-config startup-config

*Verifying Your Actions
Type this to see the configuration parameters. Of course, you can shorten this command:
Router#show running-configuration

Question 22

Question 23

Topic 5.1.4: Loading Later Releases from a TFTP Server

*Loading the Startup-Config from TFTP
The procedure for loading a startup-config file from the TFTP server into RAM is generally the same as we showed you earlier in this unit, except for the very first action, which is shown here.
For releases 10.3 and later, it is recommended that you first set the remote username in global configuration mode. If you do not specify this, the default username is used. The term rcmd refers to two protocols used for file transfer: rsp (Remote Shell Protocol) and rcp (Remote Copy Protocol).
router1#configure terminal
router1(config)#ip rcmd remote-username username
router1(config)#end

*Step 1: Specify Source
From here the commands are generally the same as for earlier releases. First, you need to copy the startup-config from the TFTP server.
Commands are issued in privileged EXEC mode.
Router1#copy tftp running-config

*Step 2: Load Host or Network File
You are now prompted to load either the host configuration file or the network configuration file. The host file is the default.
Router1#copy tftp running-config
Host or network configuration file [host]?

*Step 3: Enter Remote IP
Next, you are prompted to enter the IP address of the remote host. The configuration file resides on this remote host. The default is 255.255.255.255.
Router1#copy tftp running-config
Host or network configuration file [host]?
Address of remote host [255.255.255.255]? 204.101.202.245

*Step 4: Name Your File
Finally, you are prompted to enter the name of the configuration file, and then confirm that name. If you do not enter a file name, the default name router-confg is used.
Router1#copy tftp running-config
Host or network configuration file [host]?
Address of remote host [255.255.255.255]? 204.101.202.245
Name of configuration file [Router-confg]? router1-confg
Configure using router1-confg from 204.101.202.245? [confirm]
Connected to 204.101.202.245
Loading 1112 byte file router1-confg:![OK]
Router1#
%SYS-5-CONFIG: Configured from router1-config by tftp from 204.101.202.245

Question 24

Question 25

Question 26

Topic 5.2: Backing Up System Images

*If Flash Is Trashed
Sometimes you may have trouble loading a configuration file into your router. This may be caused or solved by the Flash memory, which stores the IOS software.
The problem could be a result of insufficient Flash memory. You should suspect insufficient Flash memory if your router experiences unexpected configurations.
You can and should backup your system image as a safety measure.

*Preventing Trouble before It Starts
You can copy your file to a TFTP or RCP (Remote Copy Protocol) server. An RCP server uses the TCP protocol to copy files to and from a file system on a remote server on the same network.
We will use the TFTP backup as an example.
Router#copy flash tftp
*Eliminating Trouble
If you do ever need your backup system image file, you can copy it back to Flash memory. The copying processes overwrites the existing Flash file.
Router#copy flash tftp

*Copying Flash to TFTP
On the next page you will see a typical response from a Flash copy command. Before examining this example, please note the following information:
  • You need to supply the source and destination filenames and the IP address of the TFTP server.
  • Each exclamation point directly indicates that ten packets — or one UDP segment — of information have been copied, and indirectly indicates that the copy process is succeeding. UDP (User Datagram Protocol) is a TCP/IP protocol that sends a packet but does not send an acknowledgment.
  • If one or more Vs are displayed, this means that there has been a successful check-run verification on a segment. Each V represents one successful verification.


*Another Backup Source
On the other hand, Flash memory may solve its own problems. Flash memory can hold multiple copies and multiple versions of the IOS software.
Therefore, Flash can work for you if you want to change the IOS version on your router, such as when you want your router IOS to match the version on the TFTP server.

Question 27

Question 28

Question 29

Topic 5.3: Loading with Boot System Commands

*The Configuration Register
If the router just cannot find a system image, such as when the Flash is corrupted, you can also use the boot system commands. Boot system commands can also be used for configuration files.
The boot system commands modify the Configuration register, which stores the vital information for loading system image and configuration files. Use the show version command to locate the Configuration register containing the system image file.

*Register Values
The Configuration register contains a hexadecimal number that tells the router where to load the system image file. Here is a brief description of what the last hexadecimal digit does:
  • 0x0 boots manually from ROM Monitor mode

  • 0x1 boots from ROM. In some routers, this means that the system image file that is loaded may be a partial file

  • 0x2 to 0xF boot from NVRAM, Flash, or the network. 0x2 defaults to Flash, if the router contains Flash memory
In our example, the system image is booted from Flash, with a register value 0x2102.

*Register Value 0x1
This command boots from ROM. The prompt tells you that you must be in global configuration mode.
After executing the config-register command you must reboot in privileged EXEC mode.
Router(config)#config-register 0x2101
Router(config)#end
Router#reload
*Register Value 0x0
This command boots from ROM Monitor mode.
Router(config)#config-register 0x2101
Router(config)#end
Router#reload

*Booting from Flash
Here are the commands for booting from Flash.
Router(config)#config-register 0x2102
Router(config)#end
Router#reload

*Boot System Commands for ROM
After you have executed the config-register command, you are ready to issue the boot system commands. Here is an example, which consists of the commands to reboot from ROM. Notice that boot system commands are executed in global configuration.
By copying the new running-config into the startup-config, you will be able to re-issue the boot system commands in the future. You can add boot system commands together and they will execute in the order that you configured them.
Router(config)#boot system rom
Router(config)#end
Router#copy running-config startup-config

*Boot System Commands for TFTP
As a second example, here are the commands to reboot from a TFTP server.
Router(config)#boot system tftp sample.exe 192.168.3.123
Router(config)#end
Router#copy running-config startup-config

*A Boot System Sequence
Here we put all of the commands together, using the ROM boot system commands as an example. As an additional backup, we could have added the TFTP commands to this code, just in case the ROM system image file doesn't load properly.
Router#show version
Router#config t
Router(config)#config-register 0x2101
Router(config)#end
Router#reload
Router#config t
Router(config)#boot system rom
Router(config)#end
Router#copy running-config startup-config

Question 30

Question 31

Topic 5.4: Removing Configuration Changes

*Levels of Changes for Earlier Releases
You can undo some configuration changes. Configuration changes are divided into three categories:
  • Noninvasive
  • Invasive
  • Last resort
The commands that we show you first are for IOS releases 10.2 and earlier.

Topic 5.4.1: Changes for Releases 10.2 and Earlier

*Noninvasive Changes
Noninvasive changes replace the running-config but not the saved start-config file. This means that you can return to the start-config file if your changes don't work.
The noninvasive changes for releases 10.2 and earlier are the changes made with configure commands, but not the write memory or write network commands.
Router#configure memory|configure network|configure terminal

*Invasive Changes
Invasive changes replace your running configuration, and essentially just involve rebooting your router. Here is the command for invasive changes on releases 10.2 and earlier.
Router#reload

*Last Resort Changes
Last resort changes return you to the default configuration before rebooting the router. Here are the commands for last resort changes on releases 10.2 and earlier:
Router#write erase
Router#reload

Topic 5.4.2: Changes for Releases 10.3 and Later

*Levels of Changes for Later Releases
Now we move on to the commands for releases 10.3 and later.

*Noninvasive Changes
The noninvasive commands are shown here. Noninvasive changes do not replace the saved start-config file. They just replace the running-config file. The noninvasive changes for releases 10.3 and later are the changes made with the configure commands, but not with a copy running-config startup-configure or copy running-config tftp command.
Router#configure memory|configure terminal|configure network

*Invasive Changes
Invasive changes replace your running configuration by rebooting your router. Here is the command for releases 10.3 and later.
Router#reload

*Last Resort Changes
Last resort changes return you to the default configuration before rebooting the router. Here are the commands for last resort changes in releases 10.3 and later.
Router#erase startup-config
Router#reload

Question 32


* Exercise 1
Try loading configuration files for your Cisco IOS router from a TFTP server. Then, assume you made some unwanted changes to running configuration parameters, and you want to undo these changes.

Examine the following table
Step Action
1 List the sequence of commands for loading configuration files from a TFTP server and from a terminal. List the commands separately for Cisco IOS releases 10.2 and earlier, as well as 10.3 and later.
2 List the sequence of commands for undoing configuration changes. List separately the commands for noninvasive, invasive, and last resort changes. Do this for both Cisco IOS release 10.2 and earlier, and 10.3 and later.


Topic 5.5: Unit 5 Summary

This course has laid the foundation for you to configure and manage your router.
You began with an examination of router startup procedures. Then you studied the different types of command-line modes. From there you learned the basic commands to navigate through the user and privileged EXEC modes: specifically, you learned context-sensitive help, editing shortcuts, and the very useful show commands.
All of this prepared you for this last unit, in which you discovered how to load configuration files. Now you are ready for actual configurations for the routers in your network.
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