router-introduction.ppt

8/13/2019 router-introduction.ppt

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12/2/2013 ITCN2

Introduction

WAN introduction and devices

MODEM technologies Router Functions

Router Hardware

Connecting to a router for the first time



12/2/2013 ITCN3

Router Function

Linking WANs and LANs

Interconnecting communication lines Path determination and packet switching

Application of security rules (ACLs)

Protocol conversion (encapsulation) – E.g. HDLC, PPP etc.



12/2/2013 ITCN5

WAN Devices

•Switch connects PCs, servers etc. to a router

•Ethernet cannot travel large distances so MODEM is used

•MODEM terminates a data circuit – data circuit-terminating

equipment (DCE)

•Communication server allows many users access to a MODEM



12/2/2013 ITCN6

Use of MODEM in WANs

•MODEM = Modulator and Demodulator

•Translates between Ethernet and WAN technology and

back again

•

Permits long distance communications



12/2/2013 ITCN7

Routers Connected by WAN

Technologies



12/2/2013 ITCN8

Some WAN Terminologies

T1=1.544 Mbps, T3=44.736 Mbps , X.25,

SMDS (SWITCHED MULTIMEGABIT DATA SERVICE

), ATM,xDSL, Modem, Cable Modem, ISDN, OC-x

X.25 and ISDN are used less today than in

the past but can still be found in operation



12/2/2013 ITCN9

Cisco Routers

Operating system is known as Internetwork

Operating System (IOS) Held in Flash memory (non-volatile)

CLI not GUI

Based on UNIX heritage



12/2/2013 ITCN10

Router Operation

Layer 3 device

Accepts PDUs on incoming network Examines PDU data

Makes decision(s) for next stage of PDU

journey

May modify PDU contents (not payload)

Passes PDU on to outgoing network



12/2/2013 ITCN11

Router Sorts Incoming Traffic

• Acts like Internet roundabout

• Allows data to get closer to

its destination

•Best path decision made by

router

•Incoming packets are switched to the most

appropriate outgoing network



12/2/2013 ITCN12

Data Link Layer and Routing

Router does not pass on layer 2 data

–

e.g. broadcasts do not pass router Layer 2 header is modified by router

Source and destination MAC addresses are

changed at each router



12/2/2013 ITCN13

Network Path Determination

Router accepts packet and views inside

Network Layer header IP address of destination carried in Network

Layer header and other information

Destination IP address looked up in routing

table

Packet passed to appropriate exit interface



12/2/2013 ITCN14

Transport Layer Determination

Transport Layer header contents examined

Source and destination port checked May trigger security of an Access Control List

May drop packets under heavy load

– UDP often first casualty



12/2/2013 ITCN15

Access Control Lists

Used to identify incoming packets

Can be used for security purposes E.g. do not allow TELNET traffic

– Identified by destination port number 23

– Found in Transport Layer header

More on ACLs later in course



12/2/2013 ITCN16

Inside a Router

Router is a dedicated computer

Contains hardware found in most PCs Does not have hard disk – Flash memory is

used instead to hold IOS

NVRAM used to hold configuration files

DRAM used to hold routing tables, buffering, ARP cache etc

CPU, ROM and interfaces too



12/2/2013 ITCN17

Internal Components of a 2600

Router



12/2/2013 ITCN18

External Connections

Configuration connections – Console and AUX

LAN connections – FastEthernet (usually)

WAN connections – often via WAN Interface

Cards (WICs) Newer hardware is modular

Makes upgrading cheaper



12/2/2013 ITCN19

External Connections on a Router



Router Connections

12/2/2013 ITCN20



12/2/2013 ITCN21

Connecting to a Router

First-time connectionmust be via console

cable attached to aPC

PC runs terminalemulator e.g.

Hyperterminal Correct parameters

must be set

9600 baud

8 data bits1 stop bitNo parity

No flow control



12/2/2013 ITCN22

Physical Connection to Router



12/2/2013 ITCN23

Conclusion

Routers choose paths and switch data packets

IOS runs on Cisco hardware Apply security etc.

No hard disk – all solid state

New routers have modular chassis for flexibility Terminal emulator and rollover cable to connect

router-introduction.ppt

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