ccna guide to cisco networking fundamentals

CCNA Guide to Cisco Networking Fundamentals

Chapter 6Router Startup and Configuration

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 2

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


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


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


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


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


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


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


IP Connectivity


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


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


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


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


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


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


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


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


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


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


CDP (continued)


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


Cisco IOS (continued)


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


Configuration Register (continued)


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


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


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)


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


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


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


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


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



• 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]



• 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


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


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


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


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 Web-based tool designed to help you configure Cisco routers

ccna guide to cisco networking fundamentals

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