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CHAPTERCHAPTERSEVENSEVEN

Router Startup and Router Startup and ConfigurationConfiguration

ObjectivesObjectives

• Understand router setup and startup

• Describe and use the Cisco Discovery Protocol

• Understand configuration management commands for Cisco routers and the 1900 series switch

• Configure IP on the Cisco router and the 1900 series switch

• Troubleshoot router connectivity problems

Router Setup and StartupRouter Setup and Startup

• A router follows a specific boot process, but processes can vary

• In general, the boot process follows these steps:– Test hardware (POST)– Load bootstrap– Locate and load Cisco IOS– Locate and load router configuration file

Router Setup and StartupRouter Setup and Startup

Figure 7-1: The boot process

POSTPOST

• Power-on self test (POST)– Diagnostic program in ROM that runs when the router

is powered on

• ROM Monitor– Bootstrap program that runs during the power-on self

test and checks basic operations of hardware

– ROM Monitor checks the configuration register for instructions regarding how to load the Cisco IOS

POSTPOST

• Configuration register allows you to control several boot functions, including:– 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

POSTPOST

Figure 7-2: Output from the show version command

POSTPOST

Table 7-1: Configuration register codes

Monitor ModeMonitor Mode

• You can set the router to enter ROM Monitor mode during the boot process by modifying the configuration register

• ROM Monitor mode– Router mode in which you can configure the

router manually– You must provide each command in the correct

syntax in order to configure the router

Cisco IOSCisco IOS

Figure 7-3: Output from the Cisco 2500 series router on bootup

Cisco IOSCisco IOS

• Trivial File Transfer Protocol (TFTP) server– Computer (such as a PC, UNIX workstation, or laptop) running

TFTP server services

Figure 7-4: Output from the show flash command

Cisco IOSCisco IOS

• Cisco routers support the following fallback options for loading the IOS:– If the IOS is configured to load from a TFTP

server, but that server cannot be located, the IOS is loaded from flash memory

– If the IOS cannot be found in flash or on a TFTP server, a minimal version of the IOS is loaded from ROM

Booting from TFTPBooting from TFTP

• You can force the router to load its IOS from a TFTP server by putting boot system commands into the configuration file

• Global configuration mode– Router mode that allows you to manipulate most

of the router’s generic settings– Prompt for global configuration mode is

router(config)#

Upgrading the IOSUpgrading the IOS

• Before loading a flash file to a router, use the show flash command to ensure there is enough free memory to load the new Cisco IOS software– The system will tell you how much memory is

used and how much is free– You may have to erase the existing flash memory

before writing onto it due to space limitations

RXBoot ModeRXBoot Mode

• Another configuration mode that you can enter when:– The changes to your system make it impossible to

boot from the flash memory– You cannot locate a valid IOS image

• The prompt from RXBoot mode is the hostname of your router followed by “boot” in parentheses

Cisco Catalyst 1900 IOS and Cisco Catalyst 1900 IOS and Configuration ManagementConfiguration Management

• To upgrade or restore IOS via TFTP, the command syntax is copy tftp://tftp_server_address/IOS_file/ opcode– The opcode command tells the device to load the file into

flash memory

• To backup configuration settings for a Catalyst 1900 switch, copy contents of NVRAM to a TFTP server– The command syntax is copy nvram

tftp://tftp_server_address/config_file_name

Router Configuration FilesRouter Configuration Files

Table 7-2: Important router copy commands

Router Configuration FilesRouter Configuration Files

Table 7-2 (cont.): Important router copy commands

Methods for Making ChangesMethods for Making Changes

• When changes to a router’s configuration or boot process are required, these basic steps can be used:– Make changes as desired to the running 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

CDPCDP

• Cisco Discovery Protocol (CDP)– Cisco proprietary Data Link layer protocol– Shares configuration information between Cisco

devices connected locally to each other– Using CDP can help you quickly determine the

network topology– With CDP, you can discover other devices on the

same LAN segment and those connected over a serial interface

CDPCDP

Figure 7-5: Show CDP neighbor command

CDPCDP

• The show CDP neighbor command supports the following options:– Ethernet– Null– Serial– Detail

• CDP was designed to be a low-overhead protocol

IP on the RouterIP on the Router

• If the router is initially configured using the extended setup program, you will be asked if you would like to enable the IP on your router– If yes, you are prompted to configure IP on each of

interface you wish to set up– If no, you can either run setup again later, or you can

configure the interfaces manually

• In the event you are configuring a serial interface as a DCE (data communication equipment), you will also need to add the clockrate command

IP on the SwitchIP on the Switch

• An IP address is not necessary on a switch like the Catalyst 1900– Switches operate mainly on Layer 2 (MAC addresses)

• You may wish to configure an IP address for your switch so you can manage it over the network via Telnet or some other management software– In order to set an IP address, you must enter Global

Configuration mode by typing configure terminal (or one of its abbreviations)

IP ConnectivityIP Connectivity

Table 7-3: Testing connectivity by layer

TelnetTelnet

• Utility that connects at the highest layer of the OSI model

• 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,

you have established that it is available on the network and that you have connectivity at all layers

IP Host NamesIP Host Names

• When telnetting to a remote router or host, the IP address of the host must follow the telnet command

• Rather than using IP addresses, it is easier to refer to a remote host or router using a name

• Sometimes, you cannot gain connectivity because the host name that you are trying to connect with is entered in a table incorrectly

• Using a name server provides name resolution from one location, making a table configuration on each device unnecessary

Ping and TracePing and Trace

• If you can’t get connectivity at the Application layer, try connectivity at the Internetwork layer

• Ping and trace verify connectivity at the Internetwork layer– Both use ICMP messages to verify the destination host is

reachable, and if not, give possible reasons for the problem

• Ping sends a packet to the destination and waits for a response– By default, the ping utility with Cisco routers is configured

to send five packets to the target

Ping and TracePing and Trace

• Ping can return the following replies:– !– .– U– C– I– ?– &

Ping and TracePing and Trace

• Extended mode ping– Options include:

• The destination address of the ping

• The protocol

• Repeat count

• Datagram size

– Can only be accessed from the privileged mode prompt

Ping and TracePing and Trace

• If ping indicates a problem with connectivity, using trace may provide a better clue as to the source of the connectivity problem

• Trace command is similar to ping command, except that the replies are requested at each hop along the way to the destination

• Trace sends multiple ICMP packets with progressively higher TTL counters until the packet reaches the destination

Ping and TracePing and Trace

• The following responses can be returned by a trace:– !H– P– N– U– *

IP RouteIP Route

• If you cannot get connectivity using ping or trace, you should check your routing table

• You can issue the show ip route command from the enable mode prompt– This command shows the routing table

• Typically, routing tables are dynamically created when routing protocols are configured on the router

Checking the InterfaceChecking the Interface

• On of the biggest mistakes made when troubleshooting is not checking the interfaces on the router

• If the interfaces are down, packets cannot be delivered

• Router interfaces go down for a variety of reasons including:– Incorrect IP configuration

– Cable problems

Checking the InterfaceChecking the Interface

• Keepalive frames– Data frames sent between two hosts to ensure that

the connection between those hosts remains open

• Different types of interfaces can show different types of reports– For example, a Token Ring interface reports down

when there is no electrical carrier signal present

Checking the InterfaceChecking the Interface

Figure 7-6: Output from the show interfaces command

Clear CountersClear Counters

• Routers keep detailed statistics regarding the data passing across its interfaces

• Before using the show interface command, you may want to clear the existing interface information

• You can clear these statistics (counters) on the interface by using the clear interface or clear counters command

DebugDebug

• Debug command– One of the most powerful tools you can use to

obtain information from your router– Only available from privileged EXEC mode– Has numerous subcommands that allow you to

troubleshoot particular protocols– Allows you to check for specific types of traffic

on the wire

DebugDebug

Figure 7-7: Debug all command output

Chapter SummaryChapter Summary

• When the router boots, it follows a set routine

• 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, a limited version will boot from ROM

• 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

Chapter SummaryChapter Summary

• CDP is proprietary to Cisco devices• Devices share information about their interface

configurations and connections to other devices• IP configuration on Cisco switches is similar• When you configure an address for a router interface,

you must be in interface configuration mode• When you configure an IP address for a Catalyst

1900 switch, you need only be in global configuration mode

Chapter SummaryChapter Summary

• 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

• On of the most important troubleshooting commands is the show interface command