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CCNA Semester2
Module 1
WANs and Routers
Objectives
WANs characteristics
Describe the role of a router in a WAN Router components
Router connections
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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 accessbandwidth over large geographic
areas.
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WANs characteristics
A WAN operates at the physical layer and the
data link layerof the OSI reference model.
It interconnects LANs that are usually separatedby large geographic areas.
WANs provide for the exchange of data packets
and frames between routers and switches and
the LANs they support.
WAN Devices
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WAN Standards
WAN physical layerprotocols describe how to
provide electrical, mechanical, operational, and
functional connections for WAN services
WAN data link protocols describe how frames arecarried between systems on a single data link.
WAN standards and OSI model
Physical
Layer
Data Link
Layer
OSI model WAN Specifications
SMDS
X21bis
EIA/TIA-232
EIA/TIA-449
V24 V35
HSSI G.703
EIA-530
LAP
B
Frame
Relay
X25PLP
HDLC
PP
P
SDL
C
MAC
sublayer
LLC
sublayer
Network
Layer
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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
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Typical WAN Layer 2 Links
Circuit-switched
PPP, SLIP, HDLC
Telephone
Company
Packet-switched
X.25, Frame Relay, ATM
Service
Provider
Leased LineHDLC, PPP, SLIP
WAN: Data Link Layer standards HDLC
High-Level Data Link Control
IEEE standard from SDLC
Point-to-point and multipoint links
Operates over sync. links
LAPB
Link Access Procedure Balanced used by X.25 protocol
LAPD
Link Access Procedure D-channel ISDN D-Channel for control signal
LAPF Link Access Procedure Balanced Used in Frame Relay for fast frame
switching over high-quality digitalfacilities
SLIP
Serial Line Interface Protocol
Designed to carry IP packets
Being replaced by PPP
PPP
Point-to-Point Protocol
Support multiple network layerprotocols (IP, IPX, DecNET)
Operates over sync. or async. links
SDLC
Synchronous Data Link Control
Protocol IBM designed protocol
Point-to-point & multipoint links
Operates over sync. links
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A typical WAN setup
Point-to-point or
circuit-switchedconnection
CO Switch
Customer PremisesEquipment
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
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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
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Introduction to routers in a WAN
A router is a special type ofcomputer. 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 theinstructions and parameters thatcontrol the flow of traffic in andout 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.
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Router Component: RAM
RAM, also called dynamic RAM (DRAM), has the
following functions:
Stores routing tables
HoldsARP cache
Holds fast-switching cache
Performs packet buffering (shared RAM)
Provides temporary 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 DualIn-Line Memory Modules (DIMMs).
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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.
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Router Component: ROM
Maintains instructions forpower-on self test
(POST) diagnostics
Stores bootstrap program and basic operatingsystem 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 forframe entry and
exit, or connect to terminal forconfiguration
Can be on the motherboard or on a separatemodule (fixed or modular card)
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Router Component: Interfaces
LAN interfaces (Ethernet, FDDI, ATM..) and WAN
interfaces(serial, ISDN, CSUs..) have controller
chips that provide the logic for connecting thesystem 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.
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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.
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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 beused fordisasterand password recovery
procedures.
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Connecting console interfaces
Configure terminalemulation software onthe PC for with theappropriate com portand settings.
Connect the RJ-45connector of therollover cable to therouter console port.
Connect the other endof the rollover cable tothe RJ-45 to DB-9
adapter. Attach the female DB-9adapter to a PC
Summary
WANs characteristics
WANs standards and protocols
Router internal components
Router functions
Router management ports Router LAN and WAN connection
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CCNA2 Module1
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