Router Startup and Configuration

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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

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 12

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:

! 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: 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 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 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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