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
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