Introduction to RoutersIntroduction to Routers

Chapter 2

Introduction to RoutersIntroduction to Routers• Objectives:

– Describe the purpose of the IOS

– Describe the basic operation of the IOS

– Identify Features of IOS

– Identify Methods of Establishing the CLI session with the router

– Move between the user command executive (EXEC) and Privileged EXEC modes

– Establish a HyperTerminal Session

– Log into the Router

– Use the Help feature in the CLI

– Troubleshoot Command Errors

Operating Cisco IOS SoftwareOperating Cisco IOS Software• A router or switch can not function without

an operating system.

• Cisco nternetwork Operating System (IOS) is the software that controls the Routing and Switching Functions of internetworking devices.

• It is installed in all Cisco routers and Catalyst switches.

The Purpose of the IOSThe Purpose of the IOS• Basic Routing and Switching Functions

• Reliable and Secure access to Networks Resources.

• Network Scalability

Cisco IOS software featuresCisco IOS software features• Cisco IOS devices have three operating

environments:– ROM Monitor

• To recover from system failures and recover a lost password

– Boot ROM• To modify the Cisco IOS image in Flash

– Cisco IOS• Normal startup

Router User InterfaceRouter User Interface• Cisco IOS software uses a Command Line

Interface (CLI)

• The CLI environment is accessible– Through a console session (No network

configuration is required)

– Dial-up connection

– Telnet connection as a virtual terminal.

Starting a RouterStarting a Router• Initial startup of Cisco Routers

– POST

– Bootstrap is loaded from ROM

– IOS is loaded from flash, TFTP, RMON

– Config is loaded from NVRAM or TFTP into setup mode

Establish a Console SessionEstablish a Console Session• To establish a Hyper Terminal Session

– Connect the terminal with an RJ-45-to-RJ45 Rollover cable or

– RJ45-to-DB-9 or

– RJ45-to-DB-25 Adapter

Router User InterfaceRouter User Interface• The Cisco CLI uses a hierarchical structure.

• Cisco IOS Software provides a command interpreter service known as EXEC

• EXEC Access Levels:– User EXEC Mode

– Privileged EXEC mode

Router LoginRouter Login• User EXEC mode

• Privileged EXEC mode

History SizeHistory Size• To change the number of command lines the

system records during a terminal session, use the terminal history size or the history size command. – The maximum number of commands is 256.

Router InterfacesRouter Interfaces• LAN Interfaces – Ethernet, FastEhternet, Token-

Ring

Router(config)#interface ethernet 0

Router(config)#interface fa 0/0

Router(config)#interface to 0

Router(config-if)#

• Wide-area Interfaces - Serial, AUX, ISDN BRI

Router(config)#interface serial 0

Router(config-if)#

• Logical Interfaces

Router(config)#interface serial 0.1

Router(config-if)#

LAN Interfaces LAN Interfaces • Ethernet

– Many routers – 15-pin AUI Ethernet interfaces – require an external transceiver

– The AUI interface is a standard for Cisco 2500 series routers. Some of them have both types – AUI and 10BaseT Ethernet

• Fast-Ethernet– Common interfaces on Cisco routers are RJ45 and the 40-

pin DB-40 Media-Independent Interface (MII)

– 100 Mbps speed, half- and full-duplex

• Token-Ring– Set the ring speed of the interface

– Connect the token-ring interface to a MAU

WAN InterfacesWAN Interfaces• Synchronous Serial Interface

– Cable types – V.35 or RS-232

– Configure the proper encapsulation type

– Use “show controllers” command to check if the interface acts as a DTE or DCE

– If the interface is acting as a DCE – supply a clock rate• Router(config-if)#clock rate 56000

Other WAN InterfacesOther WAN Interfaces• ATM Interfaces

– Operate at OC-3 speeds and higher

– Configuring PVCs

• ISDN Interfaces– Two different type of interfaces - the ISDN BRI

and ISDN PRI

– Both interfaces must establish communications with the ISDN switch before passing data

• Asynchronous Interfaces– The AUX (Auxiliary) port on a Cisco router can be

configured as an asynchronous port

– Support dial-in modems

Router Interfaces StatesRouter Interfaces States• Interface X is down, line protocol is down

• Interface X is up, line protocol is down

• Interface X is up, line protocol is up

• Interface X is administratively down, line protocol is down

• The first listing refers to the physical layer status of the interface. To troubleshoot the physical layer issue – show controllers

• The second listing reflects the data-link status. UP – UP state reflects a successful sending and received keepalives.

DTE and DCE interfacesDTE and DCE interfaces• DTE and DCE status is determined by the

configuration of the cables attached to the interface.

Router#show controllers serial 0

……………V.35 DTE Cable

Router#show controllers serial 1

…………….V.35 DCE Cable, clockrate 56000

Router#show controllers serial 2

……………, No cable

Cable connectionCable connection• Router Ethernet 10BaseT interface to a

10BaseT hub or LAN switch – straight through cable

• One router Ethernet interface to another router Ethernet interface – crossover cable

• Direct connection between PC with Ethernet interface to a router Ethernet interface – crossover cable