Giáo trình CCNA - Chương 2

CCNA – Semester2
Module 1
WANs and Routers
Objectives
• WANs characteristics
• Describe the role of a router in a WAN
• Router components
• Router connections
WANs
Introduction to WANs
• These are the major
characteristics of WANs:
– They connect devices that are
separated by wide geographical
areas.
– They use the services of carriers
– They use serial connections of
various types to access
bandwidth over large geographic
areas.
WANs characteristics
• A WAN operates at the physical layer and the
data link layer of the OSI reference model.
• It interconnects LANs that are usually separated
by large geographic areas.
• WANs provide for the exchange of data packets
and frames between routers and switches and
the LANs they support.
WAN Devices
WAN Standards
• WAN physical layer protocols describe how to

provide electrical, mechanical, operational, and
functional connections for WAN services
• WAN data link protocols describe how frames are
carried between systems on a single data link.
WAN standards and OSI model
Physical
Layer
Data Link
Layer
OSI model WAN Specifications
SMDS
X21 bis
EIA/TIA-232
EIA/TIA-449
V24 V35
HSSI G.703
EIA-530
LAPB
Frame Relay
X25 PLP
HDLC
PPP
SDLC
MAC
sublayer
LLC
sublayer
Network
Layer
WAN: Physical Layer standards

• Describes the interface
between the DTE and the DCE
• EIA/TIA-232, V.24 (DB25)
• EIA/TIA-449 (DB37)
• EIA-530 (DB25)
• V.35 (DB34)
• X.21 (DB15)
• G.703 (BNC)
www.connectworld.net
WAN Standards: Protocols
Typical WAN Layer 2 Links
Circuit-switched
PPP, SLIP, HDLC
Telephone
Company
Packet-switched
X.25, Frame Relay, ATM
Service
Provider
Leased Line
HDLC, PPP, SLIP
WAN: Data Link Layer standards
• HDLC
í High-Level Data Link Control
í IEEE standard from SDLC
í Point-to-point and multipoint links
í Operates over sync. links
• LAPB
í Link Access Procedure Balanced
í used by X.25 protocol

• LAPD
í Link Access Procedure D-channel
í ISDN D-Channel for control signal
• LAPF
í Link Access Procedure Balanced
í Used in Frame Relay for fast frame
switching over high-quality digital
facilities
• SLIP
í Serial Line Interface Protocol
í Designed to carry IP packets
í Being replaced by PPP
• PPP
í Point-to-Point Protocol
í Support multiple network layer
protocols (IP, IPX, DecNET)
í Operates over sync. or async. links
• SDLC
í Synchronous Data Link Control
Protocol
í IBM designed protocol
í Point-to-point & multipoint links
í Operates over sync. links
A typical WAN setup
Point-to-point or
circuit-switched
connection
CO Switch
Customer Premises
Equipment

Demarcation
Local Loop
WAN service provider toll network
Trunks and switches
S S
S SS
S S
Internetwork with router
• Consistent end-to-end addressing
• Addresses that represent network topologies
• Best path selection
• Dynamic or static routing
• Switching
Academy approach to hands-on labs
• In the academy lab,
devices that make up the
WAN cloud are simulated
by the connection
between the back-to-back
DTE-DCE cables.
Routers
Introduction to routers in a WAN
• A router is a special type of
computer. It has a CPU, memory,
a system bus, and various
input/output interfaces.
• Routers need the Internetwork
Operating System software (IOS)
to run configuration files.
• Configuration files contain the

instructions and parameters that
control the flow of traffic in and
out of the routers.
Router Component: CPU
• The Central Processing Unit (CPU) executes
instructions in the operating system. Among
these functions are system initialization, routing
functions, and network interface control.
• The CPU is a microprocessor. Large routers
may have multiple CPUs.
Router Component: RAM
• RAM, also called dynamic RAM (DRAM), has the
following functions:
–Stores routing tables
–Holds ARP cache
–Holds fast-switching cache
– Performs packet buffering (shared RAM)
–Providestemporary memory for the configuration file of the router
while the router is powered on
– Loses content when router is powered down or restarted
Router Component: RAM
• RAM provides run time space for executable
Cisco IOS software and its subsystems.
• RAM is usually logically divided into main
processor memory and shared input/output (I/O)
memory.
• RAM can be upgraded by adding additional Dual
In-Line Memory Modules (DIMMs).
Router Component: NRAM
• NVRAM has the following characteristics and

functions:
– Provides storage for the startup configuration file
– Retains content when router is powered down or restarted
• In some devices it is implemented in the same
flash device.
Router Component: Flash
• Holds the operating system image (IOS)
• Allows software to be updated without removing and
replacing chips on the processor
• Retains content when router is powered down or
restarted
• Can store multiple versions of IOS software
• Is a type of electronically erasable, programmable ROM
(EEPROM)
• Adding or replacing the flash Single In-Line Memory
Modules (SIMMs) or PCMCIA cards can upgrade the
amount of flash.
Router Component: ROM
• Maintains instructions for power-on self test
(POST) diagnostics
• Stores bootstrap program and basic operating
system software, load Cisco IOS software from
Flash ro RAM
• Some routers also have a scaled down version
of the IOS that can be used as an alternative
boot source.
• Requires replacing pluggable chips on the
motherboard for software upgrades
Router Component: Interfaces
• Three types of interfaces are local-area network

(LANs), wide-area network (WANs), and
Console/AUX.
• Connect router to network for frame entry and
exit, or connect to terminal for configuration
• Can be on the motherboard or on a separate
module (fixed or modular card)
Router Component: Interfaces
• LAN interfaces (Ethernet, FDDI, ATM ) and WAN
interfaces(serial, ISDN, CSUs ) have controller
chips that provide the logic for connecting the
system to the media.
• The Console/AUX ports are serial ports used
primarily for the initial configuration of the
router.
Router Component: Power Supply
• The power supply provides the necessary power
to operate the internal components.
• Larger routers may use multiple or modular
power supplies.
• In some of the smaller routers the power supply
may be external to the router.
2600 External Connection
Management Ports
• Provides a text-based connection for the
configuration, monitoring and troubleshooting
of the router
• The common management interfaces are the
console and auxilliary ports. These are EIA-232
asynchronous serial ports.
• Computer must run a terminal emulation

program to provide a text-based session with
the router.
Management Ports Connections
Management Ports Connections
• The console port is preferred because it
displays router startup, debugging, and error
messages by default.
• The console port can also be used when the
networking services have not been started or
have failed. Therefore, the console port can be
used for disaster and password recovery
procedures.
Connecting console interfaces
• Configure terminal
emulation software on
the PC for with the
appropriate com port
and settings.
• Connect the RJ-45
connector of the
rollover cable to the
router console port.
• Connect the other end
of the rollover cable to
the RJ-45 to DB-9
adapter.
• Attach the female DB-9
adapter to a PC
Summary
• WANs characteristics

• WANs standards and protocols
• Router internal components
• Router functions
• Router management ports
• Router LAN and WAN connection
Module 2
Introduction to Router
Objectives
• Function and operation of IOS
• Establishing session and log into router
• CLI help features
Operating Cisco IOS Software
Purpose of Cisco IOS Software
• Basic routing and switching functions
• Reliable and secure access to networked
resources
• Network scalability
Router user interface
• The Cisco IOS software uses a command-line
interface (CLI) as the traditional console
environment.
• This environment is accessible through several
methods:
– Console
–AUX
– Telnet
Router user interface modes
• The Cisco (CLI) uses a hierarchical structure.
• Each configuration mode is indicated with a distinctive prompt and
allows only commands that are appropriate for that mode. The IOS

provides a command interpreter service known as the command
executive (EXEC).
User EXEC and Privileged EXEC
• The user EXEC mode
allows only a limited
number of basic
monitoring commands.
This is often referred to
as a “view only” mode.
• The privileged EXEC
mode accesses all router
commands. This mode
can be configured to
require a password from
the user before accessing
it.
Operating Environment
• 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.
• Boot ROM mode use a limited subset of the Cisco
IOS feature set, is used primarily to replace Cisco
IOS image that is stored in flash.
Check for IOS
• To see the IOS image and version that is
running, use the show version command, which
also indicates other system settings.
• The show flash command is used to verify that
the system has sufficient memory to load a new

Cisco IOS image
Command: show version
ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version
11.0(10c), RELEASE SOFTWARE (fc1)
LAB_A uptime is 0 minutes
System restarted by reload
System image file is "flash:c1700-ny-mz.122-13.T8.bin", booted
via flash
cisco 2500 (68030) processor (revision N) with 6144K/2048K bytes
of memory.
Processor board ID 09218746, with hardware revision 00000000
Bridging software.
X.25 software, Version 2.0, NET2, BFE and GOSIP compliant.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2102
Command: show flash
System flash directory:
File Length Name/status
1 5895768 c1700-ny-mz.122-13.T8.bin
[5895832 bytes used, 2492776 available, 8388608 total]
8192K bytes of processor board System flash (Read ONLY)
Starting a Router
Router Startup Sequence
Setup Mode
• Setup is not intended as the mode for entering
complex protocol features in the router.

• Setup mode is to install a minimal configuration
for a router, unable to locate a configuration
from another source.
• Setup mode is called when there is no
configuration file at startup or when user issue
setup command
Setup Mode
• At startup, if you see the question “Would you like to enter the
initial configuration dialog?”, answer no.
• Jump out of setup mode without saving by pressing Ctrl+C
Router LED indicators
• Cisco routers use LED indicators to provide
status information.
• An interface LED indicates the activity of the
corresponding interface.
• The green OK LED will be on after the system
initializes correctly.
Initial Bootup
Logging into the router
User Mode
Privileged Mode
Config Mode
Interface config
Line config
Router config
• A user must login to the router before any
other commands are entered.