Download CCNA2 Chapter 1 Wide Area Networks and Routers

CCNA2 Chapter 1
Wide Area Networks and Routers
WAN – Wide Area Networks
WAN is a data communications network that operates beyond a LAN’s
geographic scope.
Users subscribe to a WAN provider such as AT&T, Sprint, etc. These
providers offer network services such as:
• Frame Relay
• Integrated Services Digital Network (ISDN)
• Asynchronous Transfer Mode (ATM)
These services carry different traffic types: voice, data and video.
WAN’s operate at the first three layers of the OSI. (Frame Relay actually
operates at layer 1 and layer 2.) All of the WAN services have layer 1 &
layer 2 in common.
Other characteristics of WAN are:
1.
operate past LAN geographic area
2.
use serial connections
3.
provide full-time & part-time connectivity
Router Internal Components
• Main internal components of the router
1. Random-access memory (RAM)
2. Nonvolatile random-access memory (NVRAM)
3. Flash memory
4. Read-only memory (ROM)
5. Interfaces
Router Internal Components
•RAM
•
stores routing tables
•
holds ARP cache
•
holds fast-switching cache
•
performs packet buffering
•
maintains packet-hold queues
•
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 Internal Components
NVRAM
• provides storage for the startup configuration file
• retains content when router is powered down or restarted
Router Internal Components
Flash memory
• holds the operating system image (IOS)
• allows software to be updated without removing & replacing chips on
the processor
• retains content when router is powered down or restarted
• can store multiple versions of IOS software
• is electronically erasable, programmable ROM (EEPROM)
Router Internal Components
ROM
• maintains instructions for power-on self test (POST) diagnostics
• stores bootstrap program & basic operating system software
• requires replacing pluggable chips on the motherboard for software
upgrades
Router Internal Components
Interfaces
• connect router to network for frame entry and exit
• can be on the motherboard or on a separate module
• connect the router to LANs and WANs
Router Internal Components
RAM is used for
routing table
information and it
holds the running
configuration.
NVRAM is used to
store the
backup/startup
configuration file. Flash memory is
used for storage of
full Cisco IOS
software images.
The interfaces
provide LAN and
WAN connectivity.
ROM is used for
permanently
storing startup
diagnostic code.
The console port
provides physical
access for initial
configuration.
Subscriber to Provider Interface
Modem
Router
DTE
DCE
Example: interface between the Data Terminal Equipment (DTE) such as a
router to the Data Circuit-Terminating equipment (DCE) to the WAN network
such as a modem.
DTE is on the customer’s side of the network. - converts user information into
signals for transmission, or reconverts the received signals into user
information
The DCE - is typically a modem and in many cases is circuitry in a CO, switch
which is made up of a CSU/DSU (Channel Service Unit/Data Service Unit).
The major reason for CSU/DSU is to protect the equipment from CPE/DTE
from aberrant voltages, and to ‘square’ up the signal.
DCE is usually on the provider’s side. - A device that establishes, maintains
and terminates a session on a network. It may also convert signals for
transmission. It
Sample Lab Setup
Subscriber to Provider Interface
EIA/TIA-232, V.35, X.21, HSSI, others
Modem
Router
DTE
DCE
Router Physical Characteristics
The 3 basic types of connections on a router are:
1.
LAN interfaces
2.
WAN interfaces
3.
Management ports
•
Console
•
auxiliary
Router Physical Characteristics
Management ports provide
•
Text-based connection
•
Configuration, monitoring, password recovery and troubleshooting
The management ports:
• EIA-232 asynchronous serial ports
• used for non-network connections
• used for initial router configuration
• to connect to a port, a PC must have a terminal emulation program
• rollover cable from PC to the management ports
Management Ports
The console port, says Cisco is preferred when troubleshooting:
• doesn’t depend on network services
• displays start and error messages by default
To establish a connection between PC and a router, one needs
• terminal emulation software
• rollover cable
• RJ-45 to DB-9 connector
Router Physical Characteristics
Cisco says, the terminal emulation software, HyperTerminal, the
parameters used to configure a router are:
•
Data bits
•
Stop bits
•
parity
Router’s connection LAN and WAN
For a PC of a LAN to connect to a router, one
• straight-thru cable from the PC to a HUB or switch
• straight-thru cable from the HUB or switch to router’s Ethernet interface
Router’s connection LAN and WAN
An internetwork must include:
• switching
• dynamic or static routing
• consistent end-to-end addressing
Router’s connection LAN and WAN
EIA/TIA-232, V.35, X.21, HSSI, others
Modem
Router
DTE
DCE
The connections to WAN on router is through the serial interface, either as a Smart
Serial interface connector or DB-60 connector.
The following devices are used in the construction of a WAN:
• communication servers
• routers
• modems
Router vs. PC
According to Cisco, the common components between a router and PC are:
1. CPU
2. input/output interfaces
3. system bus
OSI Model
Data unit
Host
layers
Media
layers
Layer
Function
Application
Network process to application
Presentation
Data representation and encryption
Session
Interhost communication
Segments
Transport
End-to-end connections and reliability (TCP)
Packets
Network
Path determination and logical addressing (IP)
Frames
Data link
Physical addressing (MAC & LLC)
Bits
Physical
Media, signal and binary transmission
Data