WXES2106
Network Technology
Semester 1 2004/2005
Chapter 5
Routers
CCNA2: Module 1 and 2
Contents
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Introduction
Routers
Cisco IOS Software
Router Mode
Starting a Router
Introduction
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A WAN is a data communications network that spans a
large geographic area
They use the services of carriers and serial connection
Devices used in WANs:
 Routers
 Modems
 Channel service units/digital service units
(CSU/DSUs)
 Terminal Adapters/Network Termination 1 (TA/NT1s)
 Communication servers
WAN operate at the physical layer and at the data link
layer.
Introduction
Introduction
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WAN physical layer describes the interface between the
data terminal equipment (DTE) and the data circuitterminating equipment (DCE).
DCE is the service provider and the DTE is the
attached device.
Introduction
Data Link Protocol
Routers
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A router is a special type of computer that has a CPU,
memory, a system bus, and various input/output
interfaces.
Routers connect and allow communication between two
networks
Routers need the Internetwork Operating System
(IOS) software to run configuration files.
Routers are the backbone devices of large intranets and
of the Internet.
They operate at Layer 3 of the OSI model.
The two main functions of a router are to select the best
path for packets and to route packets to the proper
interface.
Routers
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To accomplish this, routers build routing tables and
exchange network information with other routers.
The main internal components of the router are
 random-access memory (RAM)
 nonvolatile random-access memory (NVRAM)
 flash memory
 read-only memory (ROM)
 interfaces.
Routers
Routers
Routers
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RAM
 It is used for routing table information, fast switching
caches, running configurations, and packet queues.
 Stores routing tables
 Holds ARP cache and fast-switching cache
 Performs packet buffering
 Maintains packet-hold queues
 Provides temporary memory for the configuration file
of a router while the router is powered on
 Loses content when a router is powered down or
restarted
Routers
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NVRAM
 It is used to store the startup configuration.
 Provides storage for the startup configuration file
 Retains content when a router is powered down or
restarted
ROM
 Maintains instructions for power-on self test (POST)
diagnostics
 Stores bootstrap program and basic operating system
software
 Requires replacing pluggable chips on the
motherboard for software upgrades
Routers
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Flash
 It is used for storage of a full Cisco IOS software
image.
 Allows software to be updated without removing and
replacing chips on the processor
 Retains content when a router is powered down or
restarted
 Can store multiple versions of IOS software
 Is a type of electrically erasable programmable readonly memory (EEPROM)
Routers
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CPU
 Executes instructions in the operating system.
Buses
 Communicate between the CPU and the interfaces or
expansion slots.
Interfaces
 Connect routers to a network for frame entry and exit
 Can be on the motherboard or on a separate module
 Three types of interfaces are LANs, WANs, and
console or auxiliary (AUX).
Routers
Routers
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LAN Interface
 Allow routers to connect to the LAN media
 Some form of Ethernet
WAN Interface
 Serial connections
 An external device such as a CSU is required to
connect the router to the local connection of the
service provider.
Console and Auxiliary (AUX) ports
 Management ports
 Required for the configuration of the router
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Use RS-232 ASCII terminal or rollover cable
Routers
Routers
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Console
port
is
a
management port that is to
setup the initial configuration
of a router and to monitor it.
A rollover cable and an RJ45 to DB-9 adapter are used
to connect a PC to the
console port.
Terminal emulation software
such as HyperTerminal is
usually used.
Routers
8 Pin Connections for Cisco Router
Cisco IOS Software
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Cisco IOS is the embedded software architecture in
all of the Cisco routers and is also the operating
system of the Catalyst switches.
It provides the following network services:
 Basic routing and switching functions
 Reliable and secure access to networked resources
 Network scalability
The command-line interface (CLI) is accessed through
a console session. A console uses a low speed serial
connection directly from a computer or terminal to the
console connection on the router.
It can also be accessed remotely through a dialup
connection using a modem connected to the router AUX
port.
Cisco IOS Software
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A third method of accessing a CLI session is to Telnet to
the router. To establish a Telnet session to the router, at
least one interface must be configured with an IP
address, and virtual terminal sessions must be
configured for login and passwords.
Cisco IOS Naming Convention
 The platform on which the image runs
 The special features supported in the image
 Where the image runs and whether it has been zipped
or compressed
Router#show version
 Check the current image and available flash.
 Check the amount of RAM
 Display information about Cisco IOS
Cisco IOS Software
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Router#show flash
 Check the amount of flash memory
Cisco IOS devices have three distinct operating
environments or modes:
 ROM monitor
 Boot ROM
 Cisco IOS
At startup, a Cisco router normally loads into RAM and
executes one of these operating environments.
A system administrator can use the configuration
register setting to control the default startup mode for a
router.
Cisco IOS Software
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The ROM monitor performs the bootstrap process and
provides low-level functionality and diagnostics.
It is used to recover from system failures and to recover
a lost password.
It can only be accessed by way of a direct, physical
connection through the console port.
Boot ROM allows write operations to flash memory
and is used primarily to replace the Cisco IOS image
Router#copy tftp flash
 Copies an IOS image that is stored on a TFTP server
into the flash memory
Router Mode
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Cisco CLI uses a hierarchical structure. It requires entry
into different modes to accomplish particular tasks.
These levels are user EXEC mode and privileged EXEC
mode.
User EXEC mode
 Allows only a limited number of basic monitoring
commands.
 View only mode.
 identified by the > prompt.
Router Mode
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Privileged EXEC mode
 Provides access to all router commands.
 Allows only authorized users to access the router.
 Global configuration mode and all other more specific
configuration modes can only be reached from the
privileged EXEC mode.
 Identified by the # prompt.
Router Mode
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Router#enable password
 set a password for privileged EXEC mode.
 No encryption
Router#enable secret
 set a password for privileged EXEC mode
 With encryption
Router#configure terminal
 enter global configuration mode
Router(config)#exit, end or ctrl-Z
 Return to privileged EXEC mode from
configuration mode
global
Starting a Router
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A router initializes by loading the bootstrap, the operating
system, and a configuration file.
If the router cannot find a configuration file, it enters
setup mode.
Upon completion of the setup mode, a backup copy of
the configuration file may be saved to NVRAM.
Startup routines must accomplish the following:
 Verify that the router hardware is tested and
functional.
 Find and load the Cisco IOS software.
 Find and apply the startup configuration file or enter
the setup mode.
Starting a Router
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When a Cisco router powers up, it performs a power-on
self test (POST). These diagnostics verify the basic
operation of the CPU, memory, and network interface
ports.
After the POST, router initializes:
 Execute bootstrap loader that tests hardware and
initializes the IOS for operation.
 The boot field of the configuration register determines
the location that is used to load the IOS.
 The operating system image is loaded.
 The configuration file saved in NVRAM is loaded into
main memory and executed one line at a time.
Starting a Router
If no valid configuration file exists in NVRAM, the
operating system searches for an available TFTP
server.
 If no TFTP server is found, the setup dialog is
initiated.
In the setup mode, default answers appear in square
brackets [ ] following the question.
Ctrl-C is used to terminate setup
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Starting a Router
Starting a Router
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NVRAM invalid, possibly due to write erase
 The router has not been configured yet or that the
NVRAM has been erased.
 The factory-default setting for the configuration
register is 0x2102, which indicates that the router
should attempt to load a Cisco IOS image from flash
memory.
Starting a Router
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All Cisco routers include a TIA/EIA-232 asynchronous
serial console port. The console port is an RJ-45.
A console terminal is an ASCII terminal or PC that runs
terminal-emulation software such as HyperTerminal.
Use an RJ-45 to RJ-45 rollover cable with a female RJ45 to DB-9 adapter to connect this type of a PC to the
console port.
The default parameters for the console port are 9600
baud, 8 data bits, no parity, 1 stop bit, and no flow
control.
Starting a Router
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?
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display a list of available commands.