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IP Routing: an

Introduction

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Quiz

0-31

32-63

64-95

96-127128-159

160-191

192-223

224-255

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Routing

IP routing is the process of movingpackets from one network to another

network using routersA routing protocolis a tool used by routers

to dynamically find all the networks in theinternetwork, as well as to ensure that allrouters have the same routing table. Ex:RIP, OSPF

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Once all routers know about all networks,a routed protocolcan be used to send

user data (packets) through theestablished internetwork. Routed protocolsare assigned to an interface anddetermine the method of packet delivery.

Examples of routed protocols are InternetProtocol (IP) and IPv6.

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Routing Basic

Routers dont really care about hoststhey onlycare about networks and the best path to eachnetwork

The logical network address of the destinationhost is used to get packets to a network througha routed network

Hardware address of the host is used to deliverthe packet from a router to the correctdestination host.

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What should router knows ?

Destination address

Neighbor routers from which it can learn

about remote networks Possible routes to all remote networks

The best route to each remote network

How to maintain and verify routinginformation

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Learn about remote networks

From neighbor routers or from an

administrator.

The router then builds a routing table

If a network is directly connected, then the

router already knows how to get to it.

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Static and Dynamic Routing

Static routing, someone hand-type all network locationsinto the routing table

In dynamic routing, a protocol on one router

communicates with the same protocol running onneighbor routers.

The routers then update each other about all thenetworks they know about and place this information intothe routing table.

If a change occurs in the network, the dynamic routingprotocols automatically inform all routers about the event

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IP Routing Process

PC want to ping the laptop

IP determines whether the destinationaddress is local or remote

a remote request, the packet needs to besent to the default gateway

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For this packet to be sent to the default

gateway, the hardware address of the

routers interface Ethernet 0 (configuredwith the IP address of 172.16.20.10) must

be known.

Why ?

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LAN driver is used to provide media access type

A frame is generated

No remote host MAC address !!

When the frame is completed, its handed downto the Physical layer (ex: twisted pair)

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The router received the packet

Every device within the collision domainreceives these bits and builds the frame

Check the FCS Check the HW address

If its a match, then the Ether-Type field ischecked to find the protocol used at the

Network layer The packet is pulled from the frame, the

packet is then handed to IP.

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Router routes the packet

IP receives the packet and checks the IP

destination address

It is not router IP, check routing table

The routing table must have an entry for

the network 192.168.10.0

Otherwise discarded, network

unreachable message

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The router packet-switches the Ethernet 1

Packet is in the Ethernet 1 buffer, IP needs to

know the hardware address of the destinationhost

First checks the ARP cache or ARP request

Packet is framed send in physical layer

Remote host accept the frame

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At the destination

The destination host receives the frame,

and immediately runs a CRC.

If the result matches whats in the FCSfield, the hardware-destination address is

then checked.

If the host finds a match, the Ether-Typefield is then checked, give to IP

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At the Network layer, IP receives the packet and

checks the IP destination address.

Because theres finally a match made, theProtocol field is checked to find out whom the

payload should be given to.

The payload is handed to ICMP

ICMP send an echo reply

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Static and Dynamic Routing

When a router receives a packet for a

network that isnt listed in the routing table

It doesnt send a broadcast looking for theremote networkthe router just discards

the packet

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Dynamic Routing

IGP is interior and EGP is exterior routing of anautonomous system (AS).

An autonomous system is a collection of networks orsubnets that are in the same administrative domain

IGP operates and routes within an AS and an EGPworks outside or between more than one AS.

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Packet tracer static routing