CCNA Guide to Cisco Networking Fundamentals Fourth Edition

1
CCNA Guide to Cisco Networking Fundamentals
Fourth Edition

• Chapter 6
• Router Startup and Configuration

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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

3
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
• routershow 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
• ! Successful receipt of the ICMP echo
• . Request timed out
• U Destination was unreachable
• C Congestion experienced
• I 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 Indicates that a router received, but did not
  forward, the ICMP echo request
• P Protocol unreachable
• N Network unreachable
• U 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 routershow 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
• routerclear 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
  routers 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 CtrlBreak several times within the first
  60 seconds of bootup
• At the rommon 1gt prompt, type confreg 0x2142 and
  press Enter
• Enter the reset command at the rommon 2gt 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
• Routerconfig 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 routers 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
• Ciscos Security Device Manager (SDM) is a
  Web-based tool designed to help you configure
  Cisco routers