Module 5 - Network Layer.pptx

7/27/2019 Module 5 - Network Layer.pptx

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NETWORK LAYER

PHM VN TNH, Ph.D.

PART5OSI NETWORK LAYER


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Khoa CNTTH Nn Lm TP. HCM 2014 2/111

Objectives

Identify the role of the Network Layer, as it describescommunication from one end device to another enddevice.

Examine the most common Network Layer protocol,Internet Protocol (IP), and its features for providing

connectionless and best-effort service. Understand the principles used to guide the division

or grouping of devices into networks.

Understand the hierarchical addressing of devices andhow this allows communication between networks.

Understand the fundamentals of routes, next hopaddresses and packet forwarding to a destination

network.


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Introduction The protocols of the OSI model Network layer specify

addressingand processes that enable Transport layer data to be

packaged and transported. The Network layer encapsulationallows its contents tobe passed to thedestination within

a network or onanother networkwith minimum

overhead.


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Functions of Network Layer

The major functions of the network layer:

Defines a packet and an addressing scheme.The network layer's addressing scheme is used bydevices to determine the destination of data as itmoves through the network

Find the best path through the network.Path determination is the process that the routeruses to choose the next hop in the path for thepacket to travel to its destination. This process isalso called routing the packet.

Communication between separate networks.


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Role of the Network Layer

Network Layer Communication from Host toHost

Layer 3 uses four basic processes:

Addressing

Encapsulation

Routing: Intermediary devices that connect thenetworks are called routers. The role of the routeris to select paths for and direct packets toward their

destination. This process is known as routing. Decapsulation


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Encapsulation


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De-Encapsulation



Network Layer Protocols

Protocols implemented at the Network layer that carryuser data include:

Internet Protocol version 4 (IPv4)

Internet Protocol version 6 (IPv6)

Novell Internetwork Packet Exchange (IPX)

AppleTalk

Connectionless Network Service (CLNS/DECNet)



Network Layer and Internet Protocol

The Internet Protocol was designedas a protocol with lowoverhead.It provides only the functions that are necessary to

deliver a packet from a source to a destination over aninterconnected system of networks



The IPv4 Protocol Connectionless



The IPv4 Protocol Best Effort

Best Effort Service (unreliable)

Describe the implications for the use of the IP protocolas it is considered an unreliable protocol

Unreliable means simply that IP does not havethecapability to manage, and recover from, undelivered

or corrupt packets



The IPv4 Protocol Media Independent

IPv4 and IPv6 operate independently of the media thatcarry the data at lower layers of the protocol stack

One major characteristic of the media that the Networklayer considers: the maximumsize of PDU that eachmedium can transport:the MaximumTransmissionUnit (MTU)



Packaging the Transport Layer PDU

The process of encapsulating data by layer enablesthe services at the different layers to develop andscale without affecting other layers.

Routers can implement these different Network layerprotocols to operate concurrently over a network to

and from the same or different hosts.



IPv4 Packet Header



Network layer fields

indicates the version of

IP currently used (4 bits)

indicates the datagram

header length in 32 bit

words (4 bits)

specifies the level of

importance that a particular

upper layer protocol hasassigned (8 bits)

specifies the length of the entire

IP packet, including data and

header, in bytes (16 bits)contains an integer that identifies

the current datagram (16 bits) This

is the sequence number

3-bit field in which the 2 low-order bits control

fragmentation - one bit specifying whether the

packet can be fragmented, and the second

whether the packet is the last fragment in a

series of fragmented packets (3 bits)

the field that is used to help

piece together datagram

fragments (13 bits)




maintains a counter that gradually

decreases, by increments, to zero, at

which point the datagram is

discarded, keeping the packets from

looping endlessly (8 bits)

indicates which upper-layer protocol,such as TCP or UDP, receives

incoming packets after IP processing

has been completed (8 bits)

helps ensure IP header

integrity (16 bits)




specifies the sending node IP

address, 32 bitsspecifies the receiving node IP

address, 32 bits

allows IP to support various

options, such as security,

variable length.

extra zeros are added to this field

to ensure that the IP header is

always a multiple of 32 bits

contains upper-layer information,

variable length up to 64 KB


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Networks

Dividing Hosts into Groups



Separating Hosts into Common Groups

Networks can be grouped based on factors thatinclude:

Geographic location

Purpose

Ownership

Geographic




Purpose: Users who have similar tasks typically usecommon software, common tools, and have commontraffic patterns




Ownership: Using an organizational (company,department) basis for creating networks assists incontrolling access to the devices and data as well asthe administration of the networks




Ownership

h h i k



Why separate hosts into networks

Common issues with large networks are: Performancedegradation, Security issues, Address Management

h h i k




Increase network security

Wh h i k




Address management: To expect each host toknow the address of every other host would impose aprocessing burden on these network devices thatwould severely degrade their performance.

Wh t h t i t t k




Hierarchical addressing: solves the problem of devicescommunicating across networks of networks

i idi h k k f k


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Dividing the networks -Networks from networks

If a large network has to be divided, additional layersof addressing can be created. Using hierarchicaladdressing means that the higher levels of theaddress are retained; with a subnetwork level andthen the host level


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Routing

Supporting communication outside our network


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Supporting communication outside our network

To communicate with a device on another network, ahost uses the address of this gateway, or defaultgateway, to forward a packet outside the localnetwork

The router also needs a route that defines where to

forward the packet next. This is called the next-hopaddress. If a route is available to the router, the routerwill forward the packet to the next-hop router thatoffers a path to the destination network.

P k t F di


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Packet Forwarding

Describe the role of an intermediary gateway device inallowing devices to communicate across sub-dividednetworks


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If the destination host is in the same network as the sourcehost, the packet is delivered between the two hosts on the local

media without the need for a router. If the destination host and source host are not in the same

network, the packet may be carrying a Transport layer PDUacross many networks and through many routers.

IP Packet Ca ing Data End to End


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IP Packet Carrying Data End-to-End

IP Packet Carrying Data End to End


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A gateway the way out of our network


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A router makes a forwarding decision for each packet thatarrives at the gateway interface. This forwarding process is

referred to as routing. To forward a packet to a destinationnetwork, the router requires a route to that network. If a routeto a destination network does not exist, the packet cannot beforwarded

Routing table


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Routing table

The routing table stores information about connectedand remote networks. Routes in a routing table have

three main features:

Destination network

Next-hop

Metric

Packet forwarding


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Packet forwarding

Routing is done packet-by-packet and hop-by-hop. Each packetis treated independently in each router along the path.

The router will do one of three things with the packet: Forwardit to the next-hop router; Forward it to the destination host;Drop it

Packet forwarding


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Packet forwarding

If the routing table does not contain a more specific route entryfor an arriving packet, the packet is forwarded to the interface

indicated by a default route, if one exists. The default route isalso known as the Gateway of Last Resort.

Packet forwarding


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Packet forwarding

Routing Protocol- Sharing the route


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Routing Protocol- Sharing the route

Provides processes for sharing route information

Allows routers to communicate with other routers to update

and maintain the routing tables Examples: Routing Information Protocol (RIP), Interior Gateway

Routing Protocol (IGRP), Open Shortest Path First (OSPF),Border Gateway Protocol (BGP), and Enhanced IGRP (EIGRP)

Routing protocol Sharing the route


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Routing protocol Sharing the route

Routing protocols: static and dynamic routes

Static Routing


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Static Routing

Static route: routes to remote networks with theassociated next hops can be manually configuredon

the router. A default route can also be staticallyconfigured

Dynamic Routing


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Dynamic Routing

Routing protocols are the set of rules by which routersdynamically share their routing information

IP Addressing


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IP Addressing

Addressing is a key function of Network layerprotocols that enables data communication between

hosts on the same network or on different networks

IP addressing


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IP addressing

For any two systems to communicate, they

must be able to identify and locate each other

IP addressing


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IP addressing

AmericanRegistry forInternetNumbers

(Ti Vit Nam :VNNIC)

IP Addressing Structure


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IP Addressing Structure

IP Address converting


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IP Address converting

Classify and Define IPv4 Addresses


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1

Class A:

Bits:

0NNNNNNN0NNNNNNN HostHost HostHost HostHost

8 9 16 17 24 25 32

Range (1-126)

1

Class B:

Bits:

10NNNNNN10NNNNNN NetworkNetwork HostHost HostHost

8 9 16 17 24 25 32

Range (128-191)1

Class C:

Bits:

110NNNNN110NNNNN NetworkNetwork NetworkNetwork HostHost

8 9 16 17 24 25 32

Range (192-223)

1

Class D:

Bits:

1110MMMM1110MMMM Multicast GroupMulticast Group Multicast GroupMulticast Group Multicast GroupMulticast Group

8 9 16 17 2425 32

Range (224-239)

1

Class A:

Bits:

0NNNNNNN0NNNNNNN HostHost HostHost HostHost

8 9 16 17 24 25 32

Range (1-126)

1

Class B:

Bits:

10NNNNNN10NNNNNN NetworkNetwork HostHost HostHost

8 9 16 17 24 25 32

Range (128-191)1

Class C:

Bits:

110NNNNN110NNNNN NetworkNetwork NetworkNetwork HostHost

8 9 16 17 24 25 32

Range (192-223)

1

Class D:

Bits:

1110MMMM1110MMMM Multicast GroupMulticast Group Multicast GroupMulticast Group Multicast GroupMulticast Group

8 9 16 17 2425 32

Range (224-239)



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IP address classes ranges


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IP address classes ranges

CL

A

SS

1stOctetDec.

Range

1st OctetHigh

Order Bits

Network /Host ID

(N=Network,

H=Host)

Default SubnetMask

Number ofNetworks

Hosts perNetwork (usable

addresses)

A 1126*

0 N.H.H.H 255.0.0.0 126(272)

16,777,214(2 242)

B 128

191

1 0 N.N.H.H 255.255.0.0 16,382

(214- 2)

65,534

(2 162)

C 192223

1 1 0 N.N.N.H 255.255.255.0 2,097,150(2212)

254(2 82)

D 224239

1 1 1 0 Reserved for Multicasting

E 240254

1 1 1 1 0 Experimental, used for research

* Class A address 127 cannot be used and is reserved for loopback

and diagnostic functions

IP address classes ranges - summary


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IP address classes ranges summary

Type of Address in an IPv4 Network


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Three types of addresses:

Network address -The address by which we refer tothe network. All hosts in a network will have the samenetwork bits.

Broadcast address-A special address used to send

data to all hosts in the network. The broadcastaddress uses the highest address in the networkrange. This is the address in which the bits in the hostportionare all 1s. This address is also referred to as

the directed broadcast. Host addresses -The addresses assigned to the end

devices in the network



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yp



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yp



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yp

Network Address : All Host Bits = 0

Broadcast Address :All Host Bits = 1

Class A : 11.0.0.0

Class B : 172.16.0.0

Class C : 201.201.201.0

Class A : 11.255.255.255Class B : 172.16.255.255

Class C : 201.201.201.255

Subnet Mask


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Defining the Network and Host Portions

The subnet mask is 32-bit patternand created by placing a

binary 1 in each bit position that represents the networkportionand placing a binary 0in each bit position thatrepresents the host portion.

The prefix and the subnet mask are different ways of

representing the same thing -the network portion of anaddress

In 8-bit pattern, there are:

00000000 = 0 11110000 = 240

10000000 = 128 11111000 = 24811000000 = 192 11111100 = 25211100000 = 224 11111110 = 254

11111111 = 255



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g



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g



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g

ANDing process: extracts the network address fromthe IP address.



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g

Type of Communication


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yp

Unicast: Is used for the normal

host-to-hostcommunication in both a

client/server and a peer-to-peer network.

Uses the host address ofthe destination device as

the destination address andcan be routed through aninternetwork.

Three types: Unicast, Broadcast, Multicast



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Broadcast:

The process of sending a packet

from one host to all hosts in thenetwork

Host processes a broadcastaddress destination packet like

unicast address. A directed broadcast is sent

to all hosts on a specificnetwork.

The limited broadcastis used for communicationthat is limited to the hosts onthe local network.



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Multicast:

The process of sending a packetfrom one host to a selectedgroup of hosts.

Multicast transmission is

designed to conserve thebandwidth of the IPv4 network.

The multicast clients useservices initiated by

a client program tosubscribe to themulticast group.

Public and Private addresses


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Public and Private addresses


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Private Addresses:are set aside for use in privatenetworks.

10.0.0.0 to 10.255.255.255 (10.0.0.0 /8)

172.16.0.0 to 172.31.255.255 (172.16.0.0 /12)

192.168.0.0 to 192.168.255.255 (192.168.0.0 /16)

Public Addresses:are designed to be used in thehosts that are publicly accessible from the Internet.

Network Address Translation (NAT):is used to

translate private addresses to public addresses, beimplemented on a device at the edge of the privatenetwork.

Special IPv4 Addresses


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Network Addresses

Broadcast Addresses

Default Route0.0.0.0.

Link-Local Addresses

169.254.0.0 to 169.254.255.255 (169.254.0.0 /16)

These addresses can be automatically assigned

TEST-NET Addresses

The address block 192.0.2.0 to 192.0.2.255 (192.0.2.0

/24) is set aside for teaching and learning purposes. Theseaddresses can be used in documentation and networkexamples. Unlike the experimental addresses, networkdevices will accept these addresses in their configurations

Special IPv4 Addresses


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Assigning Addresses


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Static Assignment: The network administrator mustmanually configure the network information for a host

Assigning Addresses


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Dynamic Host Configuration Protocol (DHCP):enables the automatic assignment of addressing

information such as IP address, subnet mask, defaultgateway, and other configuration information.

Overview of IPv6


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In the early 1990s, the Internet Engineering TaskForce (IETF) grew concerned about the exhaustion of

the IPv4 network addresses and began to look for areplacement for this protocol. This activity led to thedevelopment of what is now known as IPv6.

Overview of IPv6


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Creating expanded addressing capabilities was the initialmotivation for developing this new protocol. Other issues were

also considered during the development of IPv6, such as:Improved packet handling

Increased scalability and longevity

QoS mechanisms

Integrated security To provide these features, IPv6 offers:

128-bit hierarchical addressing -to expand addressingcapabilities

Header format simplification -to improve packet handling

Improved support for extensions and options -for increasedscalability/longevity and improved packet handling

Flow labeling capability -as QoS mechanisms

Authentication and privacy capabilities -to integrate security


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Calculating IP Addresses

Introduction to subnetting


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Basic subnetting


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Basic subnetting


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Basic subnetting


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Dividing Networks into Right Sizes


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Extract network addresses from host addresses usingthe subnet mask. Total host 800 -> choose block

172.16.0.0/22

SUBNET SCHEME


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IP Class C : 192.168.10.0 Borrowed bits : 3Max. IP Number : 32Max. Subnet Number : 8

Subnet Mask : 255.255.255.224

Subnet 0: Subnetwork ID = Major Network Number

Subnet 7: Subnetwork Broadcast ID = Major Network Broadcast

192.168.10.0 : 192.168.10.255

Subnetting a Subnet


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Subnetting a Subnet


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Network Layer Protocols


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IP provides connectionless, best-effort deliveryrouting of packets. IP is not concerned with the

content of the packets but looks for a path to thedestination.

Internet Control Message Protocol (ICMP) providescontrol and messaging capabilities.

Address Resolution Protocol (ARP) determines thedata link layer address, MAC address, for known IPaddresses.

Reverse Address Resolution Protocol (RARP)determines IP addresses when the MAC address isknown

ICMPv4


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The purpose of these messages is to provide feedbackabout issues related to the processing of IP packets

under certain conditions, not to make IP reliable. ICMPmessages are not required and are often not allowedfor security reasons.

ICMP is the messaging protocol for the TCP/IP suite.ICMP provides control and error messages and is usedby the ping and traceroute utilities. Although ICMPuses the basic support of IP as if it were a higher-level

protocol ICMP, it is actually a separate Layer 3 of theTCP/IP suite.

ICMPv4


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The types of ICMP messages -and the reasons whythey are sent -are extensive. We will discuss some of

the more common messages. ICMP messages thatmay be sent include:

Host confirmation

Unreachable Destination or Service

Time exceeded

Route redirection

Source quench

ICMP - Testing the Local Stack


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Pinging the Local Loopback: 127.0.0.1

ICMP-Testing Connectivity to the Local LAN


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Ping Gateway

ICMP - Testing the Path


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Use tracert/traceroute to observe the path betweentwo devices as they communicate and trace the steps

of tracert/traceroute's operation

IP address assignment


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staticaddressing and dynamicaddressing

Static addressing


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You must go to each individual device and

configure it with an IP address. You should keep very meticulous records,

because problems can occur on the network ifyou use duplicate IP addresses.

Dynamic addressing


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There are a few different methods that you canuse to assign IP addresses dynamically:

RARP:Reverse Address Resolution Protocol.

BOOTP:BOOTstrap Protocol.

DHCP:Dynamic Host Configuration Protocol.

Dynamic addressing:RARP


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MAC: Known

IP: Unknown

RARP Request

RARP Reply

RARP server

Dynamic addressing:BOOTP


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MAC: Known

IP: Unknown

UDP Broadcast

UDP Broadcast

BOOTP server

MAC1IP1MAC2IP2MAC3IP3

IP Address

GatewayIP of serverVendor-specific

Dynamic addressing:DHCP


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MAC: Known

IP: Unknown

DHCP Discover

UDP Broadcast

DHCP Offer

UDP Unicast

DHCP server

IP1IP2IP3

DHCP Request

UDP Broadcast

DHCP Ack

IP AddressGatewayIP of serversAnd more


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ARP CONCEPT

Encapsulation


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Address resolution protocol


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In order for devices to communicate, the sendingdevices need boththe IP addresses and the MACaddressesof the destination devices.

When they try to communicate with devices whoseIP addresses they know, they must determine theMAC addresses.

ARPenables a computer to findthe MACaddressof the computer that is associated with an IPaddress.

Address resolution protocol


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ARP table in host


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ARP operation


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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

A B C

ARP Table:

? MACA.B.C.1.2.3

MAC?

IP10.0.2.1

IP10.0.2.9

Data

ARP operation:ARP request


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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

A B C

MACA.B.C.1.2.3

MACff.ff.ff.ff.ff.ff

IP10.0.2.1

IP10.0.2.9

What is your MAC Addr?

ARP operation:Checking


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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

A B C

MACA.B.C.1.2.3

MACff.ff.ff.ff.ff.ff

IP10.0.2.1

IP10.0.2.9

What is your MAC Addr?

ARP operation:ARP reply


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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

A B C

MACA.B.C.7.8.9

MACA.B.C.1.2.3

IP10.0.2.9

IP10.0.2.1

This is my MAC Addr

ARP operation:Caching


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10.0.2.1

A.B.C.1.2.3

10.0.2.9

A.B.C.7.8.9

10.0.2.5

A.B.C.4.5.6

A B C

ARP Table:

A.B.C.7.8.910.0.2.9

MACA.B.C.1.2.3

MACA.B.C.7.8.9

IP10.0.2.1

IP10.0.2.9

Data

ARP:Destination local


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Internetwork communication


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How to communicate with devices that are not onthe same physical network segment.

Default gateway

I d f d i i i h h


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In order for a device to communicate with anotherdevice on another network, you must supply it with

a default gateway. A default gateway is the IP address of the interface

on the router that connects to the networksegment on which the source host is located.

In order for a device to send data to the address ofa device that is on another network segment, thesource device sends the data to a default gateway.

Documents

Module 5 - Network Layer.pptx