CCNA Guide to Cisco
Networking Fundamentals
Fourth Edition
Chapter 6
Router Startup and Configuration
Objectives
•
•
•
•
Describe the steps involved in starting a router
Describe and use the Cisco Discovery Protocol
Configure IP on the Cisco router
Troubleshoot router connectivity problems
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Router Startup
• In general, the boot process follows these steps:
–
–
–
–
Test hardware (POST)
Load the bootstrap program
Locate and load the Cisco IOS
Locate and load the router configuration file
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Test Hardware (POST)
• Read-only memory (ROM) in a router
– Typically contains the power-on self-test (POST), the
bootstrap program, and often a version of the
operating system
• POST is a diagnostic test that determines if the
hardware is operating correctly
• During the POST, the bootstrap program, also called
the ROM Monitor, checks basic operations of the
attached hardware
– The ROM Monitor checks the configuration register
for instructions regarding how to load the Cisco IOS
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Router Configuration Files
• startup-config
– The router configuration file that loads during the boot
process
– Sometimes referred to as the backup configuration
• Because it is the saved version of the configuration file
• To revert to the settings in your startup-config
– Reboot the system by powering the router off and
back on again or
– Issue the reload command at the privileged EXEC
mode prompt
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Router Configuration Files (continued)
• Note that when you copy over the startup
configuration in NVRAM, that file is replaced
• When you copy to the running configuration in RAM,
the configuration files are blended
• To view the contents of the startup-config
– Type show startu-pconfig or just show start
at the enable prompt
• To see your working or running configuration
– Type show running-config or just show run at
the enable prompt
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Methods for Making Changes
• You can usually implement and test changes
without saving them to the startup configuration
• Basic steps to implement changes:
–
–
–
–
Make changes as desired to the configuration
Examine those changes
Determine if the changes meet the desired result
Remove the changes if they do not meet the desired
result, or simply reboot the router
– Copy the changes from the running configuration to
the startup configuration when they do meet the
desired result
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IP on the Router
• To manually configure IP on an interface
– You must first change to interface configuration mode
– Then, you can use the ip address command to
configure an IP address for the specific interface
• In the event you are configuring a serial interface as
a DCE (data communication equipment)
– You will also need to add the clockrate [bandwidth
in bits per second] command
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IP Connectivity
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Telnet
• Telnet
– Utility that connects at the highest layer of the OSI
model and provides remote access to other devices
• Cisco routers allow telnet connections via their
virtual terminal ports
• If you can establish telnet connectivity to a router
– It is available on the network and you have
connectivity at all layers
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IP Host Names
• Sometimes, you cannot gain connectivity because
the host name that you are trying to connect with is
entered in a table incorrectly
• To determine the address to name mapping on your
router, type:
router#show hosts
• To add an entry to your hosts file for name resolution
– Go to global configuration mode and type:
router(config)#ip host router15 192.168.5.1
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IP Host Names (continued)
• To remove that entry, type:
router(config)#no ip host router15 192.168.5.1
• To allow a name server to handle the IP address to
name resolution, type:
router(config)#ip name-server 172.33.44.1
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Ping and Trace
• Ping and Trace verify connectivity at the
Internetwork layer of the TCP/IP model
• Ping can return the following replies:
!
.
U
C
I
?
&
Successful receipt of the ICMP echo
Request timed out
Destination was unreachable
Congestion experienced
Ping interrupted
Packet type unknown
Packet TTL exceeded
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Ping and Trace (continued)
• Using the ping command alone
– Referred to as extended mode ping
– Allows you to enter your ping command step by step
• Trace sends multiple ICMP packets with
progressively higher time-to-live counters (TTL)
– Until the packet reaches the destination
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Ping and Trace (continued)
• The following responses can be returned by a trace:
!H
P
N
U
*
Indicates that a router received, but did not
forward, the ICMP echo request
Protocol unreachable
Network unreachable
Port unreachable
Request timed out
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IP Route
• If you cannot get connectivity using Ping or Trace,
you should check your routing table
• Issue the show ip route command from the
enable mode prompt
– To display the routing table
• Typically, routing tables are dynamically created
when routing protocols are configured on the router
– If you want, you can use the ip route command
from the global configuration mode
• To statically enter routes in the routing table
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Checking the Interface
• show interfaces command
– Check the configuration of a specific interface from the
enable mode prompt
– Example: router#show int s0/0
• Replies
– Serial0/0 is up, line protocol is up
– Serial0/0 is up, line protocol is down
– Serial0/0 is up, line protocol is
administratively down
– Serial0/0 is down, line protocol is down
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Checking the Interface (continued)
• Clear counters
– The router keeps detailed statistics regarding data
passing across its interfaces
– To clear the counters for interface f0/0, type:
router#clear interface f0/0
• debug command
– One of the most powerful tools you can use to obtain
information from your router
– Tool is only available from privileged EXEC mode
– Debug has numerous subcommands
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CDP
• Cisco Discovery Protocol (CDP)
– Cisco proprietary Data Link layer protocol
• Shares configuration information between Cisco devices
that are connected directly to each other
• All Cisco devices can use CDP to:
– Discover each other
– Learn about the configurations of other devices
• Using CDP can help you quickly determine the
network topology
• CDP was designed to be a low-overhead protocol
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CDP (continued)
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Cisco IOS
• Cisco IOS is usually loaded from flash memory
– If the router cannot find the IOS in flash memory, it will
look for a copy on a TFTP server
– If it cannot find one there, it will boot a minimal version
of the IOS from ROM
• If you want to see information about your router’s
flash memory:
– Type show flash from the enable mode prompt
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Cisco IOS (continued)
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Configuration Register
• Every Cisco router has a 16-bit configuration
register, which is stored in NVRAM
• This register allows you to control several boot
functions:
–
–
–
–
–
Forcing the system into the bootstrap program
Enabling or disabling the console Break function
Setting the console terminal baud rate
Loading the IOS from ROM
Loading the IOS from a TFTP server
• Examine the configuration register by typing show
version
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Configuration Register (continued)
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ROM Monitor Mode
• ROM Monitor mode
– The bootstrap program that is built into the firmware of
the router
– Used to initialize the hardware and load the IOS
– ROM Monitor can be used to perform other tasks such
as diagnostics and recovering passwords
• Configure your system to enter ROM Monitor mode
– Enter the following command at the global
configuration prompt:
router(config)#config-register 0x2100
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ROM Monitor Mode (continued)
• Configure your system to boot a smaller IOS image
from ROM and enter RxBoot mode
– Enter the following command at the global
configuration prompt:
router(config)#config-register 0x2101
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RxBoot Mode
• RxBoot mode
– A limited version of the IOS
• Entering RxBoot mode is often done intentionally
– When you want to access a TFTP server to download
a new IOS
• If your router enters RxBoot mode without your
intervention
– Indicates that the router could not find a good IOS
image
• Prompt: router(boot)
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Boot System Commands
• As long as the configuration register is configured
with a 2 as the final hexadecimal digit
– The ROM Monitor will look for boot system commands
in NVRAM during the bootup process
• Enable your system to boot an IOS file from the
TFTP server
– Issue the following command from global configuration
mode:
router(config)#boot system tftp
somefile.bin
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Backing Up and Restoring the IOS
• copy flash tftp
– The command for backing up your IOS to a TFTP
server
• You will be asked for the source filename, the IP
address of the TFTP server, and the destination
filename
• Type erase flash at the privileged EXEC mode
prompt
– To erase the IOS
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Upgrading the IOS
• Before you load a new IOS file to your router
– Use the show flash command to ensure there is
enough free memory to hold it
• The system will tell you how much memory is used
and how much is free
• If there is not enough memory to hold both the
current IOS image and the upgrade
– You will have to erase the existing flash memory as
previously mentioned
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Router Password Recovery
• Password recovery
– Process that allows you to get into the router without
the necessary passwords
– You must be physically connected to the router using
the console cable
• Steps to perform password recovery on the Cisco
2600 series:
– Connect to the router from a PC using the console
port and the HyperTerminal program
– Enter the show version command and record the
value of the configuration register
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Router Password Recovery
(continued)
• Steps to perform password recovery on the Cisco
2600 series: (continued)
– Turn the router off and on using the power switch
– Press Ctrl+Break several times within the first 60
seconds of bootup
– At the rommon 1> prompt, type confreg 0x2142 and
press Enter
– Enter the reset command at the rommon 2> prompt
– Enter no if asked to enter the system configuration
dialog
– Enter enable to get to privileged mode
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Router Password Recovery
(continued)
• Steps to perform password recovery on the Cisco
2600 series: (continued)
– Enter the copy start run command to load the
saved configuration file from NVRAM into RAM
– Enter the show run command to view the
configuration
– To change the enable secret command, enter the
following commands:
Router#config t
Router(config)#enable secret [secret
password]
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Router Password Recovery
(continued)
• Steps to perform password recovery on the Cisco
2600 series: (continued)
– Enter config-register 0x2102 at the global
configuration mode prompt to make sure the router
reboots in the default manner
– Enter the copy run start command to save your
changes
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Security Device Manager
• Security Device Manager (SDM)
– A Web-based tool primarily used for implementing and
testing security configurations
– Commonly used to configure routing protocols, WAN
services, wireless routing, firewalls, virtual private
networks (VPNs), and quality of service (QoS)
• SDM is typically not used to configure basic
functionality on a Cisco router
– In fact, SDM cannot do all things
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Summary
• When a router boots, it follows a set routine
• Although a router’s boot process can vary, the
typical boot process follows a standard sequence
• If the Cisco IOS is set to load from a TFTP server,
but the TFTP server cannot be located, then the
IOS will boot from flash memory
• If the IOS cannot be found in flash memory or on
the TFTP server, then a limited version will boot
from ROM
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Summary (continued)
• If the Cisco IOS is set to load a configuration file
from a TFTP server, but the file or server is not
available, the configuration file will be loaded from
NVRAM
• The Cisco Discovery Protocol (CDP) shares
information between Cisco devices about other
local Cisco devices
• CDP uses broadcasts to update neighbors every
60 seconds by default
• Devices share information about their interface
configurations and connections to other devices
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Summary (continued)
• You can verify router connectivity to other systems
by using telnet to determine if there is Application
layer connectivity
• If you cannot get connectivity at the Application
layer, try Trace and Ping
• One of the most important troubleshooting
commands is the show interfaces command
• Cisco’s Security Device Manager (SDM) is a Webbased tool designed to help you configure Cisco
routers
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