Router Basics

1
Chapter 10

• Router Basics

2
Learning Objectives

• Describe the benefits of network segmentation
  with routers
• Understand the elements of the Cisco user
  interface
• Configure the HyperTerminal program to interface
  with the Cisco router
• Describe the various router configuration modes
• Describe the various router passwords
• Understand the enhanced editing features of the
  Cisco IOS
• Compare router components to typical PC components

3
Chapter Overview

• The benefits of using routers is revisited.
• You will learn about the Cisco user interface
  including the
• System Configuration Dialog
• various configuration modes
• router passwords
• Also included is
• configuring the router using the HyperTerminal
  program
• enhanced editing features of the Cisco IOS

4
Benefits of Routing

• Routers provide packet-filtering, connections
  between local networks.
• This reduced traffic reduces collisions on an
  Ethernet network.
• Routers can direct packets to both local and
  remote segments.
• Bridges also keep unnecessary traffic off of
  segments for which traffic is not intended, but
  bridges do not stop broadcast traffic.
• Bridges create collision domains and routers
  create broadcast domains.
• Routers are typically the interface for WAN
  connections.

5
Cisco Router User Interface

• Users configure and interact with a Cisco router
  using the Cisco Internetwork Operating System
  (IOS).
• The Cisco IOS provides a command-line interface,
  which allows network operators to check the
  status of the router, and network administrators
  to manage and configure the router.
• The software that interprets the commands is
  called the command executive or EXEC.

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Router Access

• Network administrators can access the router
  directly via the console port on the back of the
  router.
• The router can also be accessed through the AUX
  port also located on the back of the router.
• Five virtual terminals (VTY) can be used to
  configure the router remotely.
• Using virtual terminals to access a router is
  typically called telnetting.
• Telnet is a program, which is part of the TCP/IP
  suite.

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Connecting a PC to the Console
Laptop
RJ45-DB9
Router
Rollover cable
Figure 10-1 Connecting a PC to the console
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TFTP Server

• The router can also obtain configuration
  information from a TFTP server.
• A TFTP server is a computer or router that
  maintains a copy of a routers configuration file
  or IOS so that the files can be downloaded when
  necessary.
• TFTP servers are typically used for backup.

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Accessing the Router
Figure 10-2 Methods for configuring a Cisco
router
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HyperTerminal

• When configuring the router via the console or
  aux ports, a physical connection must be made.
• Typically, this connection is between a PC
  running Windows 95, Windows 98, or Windows NT 4.0
  and the router port.
• The physical connection point on the PC will be
  the COM1 or COM2 port.
• Once the physical connection is made, use the
  HyperTerminal application to create the software
  connection.

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HyperTerminal Settings

• The following HyperTermial settings should be
  configured for the COM port
• Bits per second 9600
• Data bits 8
• Stop bits 1
• Parity None
• Flow control Xon / Xoff.
• Flow Control may also work using the Hardware or
  None setting.

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System Configuration Dialog

• If the router hasnt been previously configured,
  or if the configuration has been erased, the
  Cisco IOS automatically runs the setup command
  when the router is turned on or reloaded.
• The setup command launches the System
  Configuration Dialog.
• This prompts you for a host name for the router,
  some password configuration information, protocol
  configuration, and routing protocol selection
  (RIP and IGRP).
• When complete, the router will run through its
  typical startup and configuration process.
• At this point, the router will be operational but
  the configuration will in no way be complete.

13
User Interface

• After the router completes its initialization
  process, you must press Enter to reach the
  prompt.
• The prompt consists of two pieces
• the host name of the router
• the greater than symbol (gt).
• By default, the routers host name is router, so
  the default prompt is routergt.

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Interaction Modes

• Two primary modes for interacting with the router
  exist
• User EXEC mode (aka user mode)
• Privileged EXEC mode (aka enable mode)
• The User EXEC mode prompt is the host name
  followed by the greater than sign as described
  above.
• User mode does not allow you to actually
  configure the router.
• You also cant view everything about the router
  in this mode.

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Privileged Exec Mode

• In order to configure the router and access all
  details, you must go into the Privileged EXEC
  mode.
• This mode is entered using an enable or enable
  secret password if you have configured it.
• Once you enter the enable password or the enable
  secret password, the greater than symbol (gt) will
  change to a pound () sign (router).
• Pressing the question mark at any time, in any
  mode, activates context sensitive Help on the
  Cisco router.

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Global Configuration Mode

• There are several configuration modes that are
  accessible only through the Privileged EXEC mode.
  
• Typing config t at the enable mode prompt
  accesses the basic configuration mode, called
  global configuration mode.
• The prompt for global configuration mode is
  router(config).
• At this prompt, changes that affect the entire
  router are made, thus the term global.

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Interface Configuration Mode

• Once you have entered the global configuration
  mode, other modes are accessible.
• Interface configuration mode allows you to
  configure Ethernet, serial, and other interfaces
  on your router.
• The prompt will be router(config-if).

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Line Configuration Mode

• Line configuration mode is also accessible from
  the global configuration mode.
• This allows you to configure the virtual
  terminals, console, and AUX lines that allow you
  to access the router.
• The prompt will be router(config-line).

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Router Configuration Mode

• Yet another configuration mode accessible from
  the global configuration mode is router
  configuration mode.
• This mode allows you to enable routing protocols
  such as RIP and IGRP.
• The prompt will be router(config-router).
• You can move between the modes in several ways.
• The term going back means to go up one level
  towards user mode.

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Navigation

• Typing exit will take you back one level.
• If you are in User mode, typing exit will log you
  out of the router.
• Typing end or pressing the CTRLZ keys will take
  you all the way back to the enable prompt.
• Remember that you do not need to type the entire
  command.
• Type the fewest number of characters to uniquely
  identify the command instead.
• For example, to enter the enable mode, you can
  type enable, or just ena.
• If the command does not work, the router will
  tell you by pointing to the character with a
  caret () symbol.

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Enable Enable Secret Passwords

• The setup routine allows the user to setup three
  passwords the enable password, the enable secret
  password, and the terminal passwords.
• The enable password is used only when the enable
  secret password is not present.
• The enable password is not encrypted, but does
  restrict access to enable mode if the enable
  secret password is removed.
• The enable secret password is the primary
  password used to access enable mode because is
  supercedes the enable password.
• This enable secret password is encrypted with the
  MD5 algorithm, which has no known method of
  reversal.
• You must be in global configuration mode to
  configure the enable and enable secret passwords.

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Enable Enable Secret Example
23
More Passwords

• The console password protects the router from
  console access.
• When this password is set, someone attempting to
  access the router from the console connection
  will have to enter a password before he or she
  can enter any other commands.
• The AUX password is requested whenever someone
  attempts to access the router via a modem from
  the AUX port.
• The virtual terminal passwords are set to
  restrict users from telnetting into the router.
• If you want to configure encryption for all of
  your router passwords, enter the command service
  password-encryption at the global configuration
  prompt.
• You must be in line configuration mode to
  configure the console, aux, and virtual terminal
  passwords.

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Console Password Example
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Quick Quiz

• Name three ways an administrator can access a
  router for configuration.
• Which passwords are you prompted for during the
  System Configuration Dialog?
• What is the prompt when you are in interface
  configuration mode?
• What is the prompt when you are in global
  configuration mode?
• What is the prompt when you are in line
  configuration mode?

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Enhanced Editing

• The router supports enhanced editing features
  that allow you to modify lengthy commands.
• You can turn off the enhanced editing features by
  typing terminal no editing at either the User
  EXEC or any of the Privileged EXEC prompts.
• You can turn on terminal editing by typing
  terminal editing.
• If the router mistakes a mistyped command for a
  host name, it will, by default, attempt to lookup
  the host name.
• If you would like to prevent the router from
  doing this, type no ip domain-lookup from the
  global configuration prompt.

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Editing Commands
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Command History

• The show history command from the user or
  privileged prompt will show you the last 10
  previously typed commands.
• The terminal history size command can set the
  history buffer anywhere from 0 to 256.
• is any number between 0 and 256. The default is
  10.
• Use the up arrow or press CtrlP to retrieve
  previous commands instead of retyping them.
• Use the down arrow or CtrlN to retrieve recent
  commands instead of retyping them.
• Press the Tab key to complete the command after
  typing enough unique characters.

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Configuring Router Identification

• Most commands for configuring router
  identification must be typed in global
  configuration mode.
• The default host name is simply router. To set
  the routers name to router57, you would type
  hostname router57.
• You can also configure a banner, which will give
  a message of the day to anyone that logs in to
  the router using the banner motd command.
• You can configure a description for each of the
  interfaces physically attached to your router by
  using the description command.
• Any text typed after the word description will
  identify the interface.

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Banner Method Command
Figure 10-6 Configuring a banner message
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Banner Method Displayed
Router1 con0 is now available
Press RETURN to get started.
Welcome to the Cisco 2501 router. Enjoy!
router1gt
Figure 10-6 Configuring a banner message
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Configuring the Time and Date

• Use the clock set command in enable mode to
  configure the time and date.
• To configure the time zone, you must change to
  global configuration mode.
• The timezone command is clock timezone timezone
  - where timezone is the name of the timezone
  for example pacific and is the offset from the
  Universal Time Code.
• To confirm your settings, type show clock at the
  Privileged EXEC prompt.

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Router Components

• A router is a computer and has many of the same
  hardware components that a typical PC does.
• The important router components are
• ROM
• Flash Memory
• NVRAM
• RAM/DRAM
• Router Interfaces
• The following slides discuss each component in
  more detail.

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ROM

• Read Only Memory stores the initial bootstrap
  program that initializes the router's basic
  hardware components.
• ROM is not modified during normal operations, but
  it can be upgraded with special plug-in chips.
• The content of ROM is maintained even when the
  router is rebooted.
• In the event of a boot failure you can recover
  the system by booting into ROM monitor mode which
  has a small version of the IOS.
• You know that you are in ROM Monitor mode when
  the prompt is just a greater than sign (gt).

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Flash memory

• Flash memory is erasable, programmable, read only
  memory.
• The show version and show flash commands will
  give you information regarding the contents of
  flash memory.
• The content of flash memory is maintained even
  when the router is rebooted.
• Flash memory contains the working copy of the
  current Cisco IOS.
• This component typically initializes the IOS for
  normal router operations.
• The Cisco IOS is usually backed up on a TFTP
  server.

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NVRAM

• Non-volatile Random Access Memory is a special
  type of RAM that is not cleared when the router
  is rebooted.
• The startup configuration file for the router is
  stored in NVRAM by default.
• When the router is first shipped, the
  configuration file is not present.
• NVRAM stores all the user-defined configuration
  information for the router, which includes the
  host name of the router, the routing tables, and
  the protocol configurations.
• The configuration file is the first file that the
  person who sets up the router creates. This
  configuration file, like the IOS in flash memory,
  is typically backed up on a TFTP server.

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RAM/DRAM

• During the router boot process the startup
  configuration, which is maintained in NVRAM, is
  loaded into RAM and becomes the running
  configuration (aka the working configuration).
• Random access memory is a volatile hardware
  component because its information is not
  maintained in the event of a router reboot.
• During normal operations, changes to the routers
  running configuration take place in RAM.
• If the administrator wants to ensure those
  changes are maintained, even if the system is
  rebooted, then he or she must copy the running
  configuration to the startup configuration using
  the command copy running-config startup-config.

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Interfaces

• Routers are attached to LANs and WANs using
  configurable interfaces.
• There are various interfaces that can be
  configured on a router.
• A typical interface is Ethernet0 (aka e0), which
  is used to connect the router to an Ethernet LAN.
  
• The router can have other types of interfaces,
  including
• Token Ring
• Basic Rate Interface (BRI)
• Asynchronous Transfer Mode (ATM)
• Fiber Distributed Data Interface (FDDI)
• Channel Interface Protocol (CIP) for System
  Network Architecture (SNA)
• High Speed Serial Interface (HSSI)

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Quick Quiz

• How do you move to the beginning of a line when
  typing commands in a Cisco router?
• How do you retrieve previously typed commands so
  that you dont have to type them again?
• What is the command to stop the router from
  trying to resolve host names to IP addresses?
• What is the command to configure a message for
  those who log in to the router?
• What are the 5 components of a router?

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Chapter Summary

• Cisco routers use the Cisco IOS to provide an
  interface for network operators and
  administrators.
• There are two basic modes of operation,
  Privileged EXEC (router prompt) and User EXEC
  (routergt prompt).
• In User EXEC basic tasks such as checking the
  router status, checking connectivity, and viewing
  some configuration information can be
  accomplished.
• In order to actually configure the router,
  Privileged EXEC mode must be used.
• The Privileged EXEC mode is often called enable
  mode because it is protected by the enable
  password and/or the enable secret password.

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Chapter Summary Continued

• Passwords are set during initial configuration,
  but can be changed in global configuration mode
  after the initial configuration is complete.
• When configured, the enable secret password
  supercedes the enable password.
• The enable secret is an encrypted password that
  is not viewable in the configuration file.
• This means that the enable secret password has
  less chance of being compromised and should be
  different from the enable password for that
  reason.

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Chapter Summary Continued

• The components of a router include
• ROM Stores a limited version of the Cisco IOS
  and routines for checking the hardware during
  system boot.
• Flash memory Stores the startup copy of the
  Cisco IOS that is loaded by default during system
  boot.
• NVRAM Stores the startup copy of the router
  configuration file that is loaded by default
  during system boot.
• RAM/DRAM Stores the working copy (running
  configuration) of the router configuration. This
  configuration is erased if the router is
  rebooted, unless it is saved to the startup
  configuration.
• Interfaces Provide connectivity to various
  types of LANs and WANs.

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End of Chapter 10