Sub Netting - Apjohns0 Ch01-Where We'Ve Been

8/2/2019 Sub Netting - Apjohns0 Ch01-Where We'Ve Been

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Application

Presentation

Session

Transport

Network

Data-Link

Physical

THE OSI MODEL

Where Weve Been

Chapter 1Review

By: Allan Johnson


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Table of Contents

Enterprise

Review the OSI Model

Encapsulation

LAN Devices & Technologies

Transport Layer

IP Addressing

Go There!Go There!

Go There!Go There!

Go There!Go There!


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A New Word!Enterprise

A corporation, agency,

school, or other

organization that worksto tie together its data,

communication,

computing, and file

servers.


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Your Job as a Network Guru

Help Enterprises meet their needs by: Interconnecting their LANs so that

geographically remote services can beaccessed

Ensuring users get high bandwidth accessover their LANs (i.e. Replacing hubs withswitches; 10Mbps NICs with 10/100 MbpsNICs or Gigabit per second NICs)

Implementing new technologies as theyemerge like e-commerce, videoconferencing, voice over IP, and distancelearning.


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Application

Presentation

Session

Transport

Network

Data-Link

Physical

THE OSI MODEL

Review The Model

Open SystemsInterconnected Reference

Model

Table of Contents


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Why A Layered Model?

Reduces complexity Standardizes interfaces

Facilitates modular

engineering Ensures interoperable

technology

Accelerates evolution

Simplifies teaching &learning

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Host Layers vs. Media Layers

Application

Presentation

Session

Transport

Network

Data-Link

Physical

Host LayersProvides accuratedata deliverybetween computers

Application

Presentation

Session

Transport


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Host Layers vs. Media Layers

Application

Presentation

Session

Transport

Network

Data-Link

Physical

Media LayersControls physicaldelivery of the messageover the network

Network

Data-Link

Physical


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Application Layer

Provides network services(processes) to applications.

For example, a computer ona LAN can save files to aserver using a networkredirector supplied by NOSslike Novell.

Network redirectors allowapplications like Word andExcel to see the network.

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Presentation Layer

Provides data representationand code formatting.

Code formatting includescompression and encryption

Basically, the presentationlayer is responsible forrepresenting data so that the

source and destination cancommunicate at theapplication layer.

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Session Layer

Provides inter-host communicationby establishing, maintaining, andterminating sessions.

Session uses dialog control anddialog separation to manage the

session Some Session protocols:

NFS (Network File System)

SQL (Structured Query Language)

RCP (Remote Call Procedure)

ASP (AppleTalk Session Protocol)

SCP (Session Control Protocol)

X-window

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Transport Layer

Provides reliability, flow control,and error correction through theuse of TCP.

TCP segments the data, adding aheader with control information

for sequencing andacknowledging packets received.

The segment header also includessource and destination ports forupper-layer applications

TCP is connection-oriented anduses windowing.

UDP is connectionless. UDP doesnot acknowledge the receipt of

packets.

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Network Layer

Responsible for logicallyaddressing the packet andpath determination.

Addressing is done through

routed protocols such as IP,IPX, AppleTalk, and DECnet.

Path Selection is done byusing routing protocols such

as RIP, IGRP, EIGRP, OSPF,and BGP.

Routers operate at theNetwork Layer

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Data-Link Layer

Provides access to the media

Handles error notification,network topology issues, andphysically addressing the

frame.

Media Access Control througheither...

Deterministictoken passing Non-deterministicbroadcast

topology (collision domains)

Important concept: CSMA/CD

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Physical Layer

Provides electrical,mechanical, procedural andfunctional means foractivating and maintaining

links between systems. Includes the medium throughwhich bits flow. Media canbe...

CAT 5 cable Coaxial cable

Fiber Optics cable The atmosphere

Application

Presentation

Session

Transport

Network

Data-Link

Physical


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Application

Presentation

Session

Transport

Network

Data-Link

Physical

THE OSI MODEL

Encapsulation

Peer-to-PeerCommunications

Table of Contents


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Peer-to-Peer Communications

Peers communicate using the PDU of theirlayer. For example, the network layers of thesource and destination are peers and usepackets to communicate with each other.

Application Application

Presentation Presentation

Session Session

Transport TransportNetwork Network

Data-Link Data-Link

Physical Physical

Data

SegmentsPacketsFrames

Bits

DataData


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Encapsulation Example

You type an emailmessage. SMTP takes thedata and passes it to thePresentation Layer.

Presentation codes thedata as ASCII.

Session establishes a

connection with thedestination for the purposeof transporting the data.

Application

Presentation

Session

Transport

Network

Data-LinkPhysical


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Encapsulation Example

Transport segments thedata using TCP and hands itto the Network Layer foraddressing

Network addresses thepacket using IP.

Data-Link then encaps. thepacket in a frame and

addresses it for localdelivery (MACs)

The Physical layer sends thebits down the wire.

Application

Presentation

Session

Transport

Network

Data-LinkPhysical


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Application

Presentation

Session

Transport

Network

Data-LinkPhysical

THE OSI MODEL

LAN Devices &

TechnologiesThe Data-Link &Physical Layers

Table of Contents


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Devices

What does it do? Connects LAN

segments;

Filters traffic based

on MAC addresses;and

Separates collisiondomains based upon

MAC addresses.

What layer device?


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Devices

What does it do? Since it is a multi-port

bridge, it can also Connect LAN

segments;

Filter traffic based onMAC addresses; and

Separate collisiondomains

However, switches

also offer full-duplex,dedicated bandwidthto segments ordesktops.

What layer device?


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Devices

What does it do? Concentrates LAN

connections frommultiple devices into

one location Repeats the signal (a

hub is a multi-portrepeater)

What layer device?


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Devices

What does it do? Interconnects networks

and provides broadcastcontrol

Determines the path

using a routing protocolor static route

Re-encapsulates thepacket in the appropriateframe format and

switches it out theinterface

Uses logical addressing(i.e. IP addresses) todetermine the path

What layer device?


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Media Types


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LAN Technologies

Three MostCommon UsedToday inNetworking


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Ethernet/802.3

Cable Specifications: 10Base2

Called Thinnet; uses coax

Max. distance = 185 meters (almost 200)

10Base5 Called Thicknet; uses coax

Max. distance = 500 meters

10BaseT Uses Twisted-pair

Max. distance = 100 meters

10 means 10 Mbps


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Ethernet/802.3

Ethernet is broadcast topology. What does that mean?

Every devices on the Ethernet segment seesevery frame.

Frames are addressed with source anddestination ______ addresses.

When a source does not know the destination orwants to communicate with every device, it

encapsulates the frame with a broadcast MACaddress: FFFF.FFFF.FFFF

What is the main network traffic problemcaused by Ethernet broadcast topologies?


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Ethernet/802.3

Ethernet topologies are also sharedmedia.

That means media access is controlled

on a first come, first serve basis. This results in collisions between the

data of two simultaneously transmitting

devices. Collisions are resolved using what

method?


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Ethernet/802.3

CSMA/CD (Carrier Sense Multiple Access withCollision Detection)

Describe how CSMA/CD works: A node needing to transmit listens for activity on

the media. If there is none, it transmits. The node continue to listen. A collision is detected

by a spike in voltage (a bit can only be a 0 or a 1--itcannot be a 2)

The node generates a jam signal to tell all devices

to stop transmitting for a random amount of time(back-off algorithm).

When media is clear of any transmissions, the nodecan attempt to retransmit.


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Address Resolution Protocol

In broadcast topologies, we need a way toresolve unknown destination MAC addresses.

ARP is protocol where the sending devicesends out a broadcast ARP request which

says, Whats you MAC address? If the destination exists on the same LAN

segment as the source, then the destinationreplies with its MAC address.

However, if the destination and source areseparated by a router, the router will notforward the broadcast (an important functionof routers). Instead the router replies with its

own MAC address.


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Application

Presentation

Session

Transport

Network

Data-LinkPhysical

THE OSI MODEL

Transport Layer

A Quick Review

Table of Contents


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Transport Layer Functions

Synchronization of the connection Three-way handshake

Flow Control

Slow down, youre overloading my memorybuffer!!

Reliability & Error Recovery

Windowing: How much data can I sendbefore getting an acknowledgement?

Retransmission of lost or unacknowledgedsegments


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Transports Two Protocols

TCP Transmission Control

Protocol

Connection-oriented

Acknowledgment &Retransmission ofsegments

Windowing

Applications: Email

File Transfer

E-Commerce

UDP User Datagram

Protocol

Connectionless

NoAcknowledgements

Applications: Routing Protocols

Streaming Audio Gaming

Video Conferencing


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Application

Presentation

Session

Transport

Network

Data-LinkPhysical

THE OSI MODEL

IP Addressing

Subnetting Review

Table of Contents


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Logical Addressing

At the network layer, we use logical,hierarchical addressing.

With Internet Protocol (IP), this address is a32-bit addressing scheme divided into four

octets. Do you remember the classes 1st octets

value? Class A: 1 - 127

Class B: 128 - 191 Class C: 192 - 223

Class D: 224 - 239 (multicasting)

Class E: 240 - 255 (experimental)


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Network vs. Host

N H H HClass A:27 = 126 networks; 224 > 16 mill ionhosts

N N H HClass B : 214 = 16,384 networks; 216 > 65,534 hosts

N N N HClass C : 221 > 2 million networks; 28 = 254hosts


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Why Subnet?

Remember: we are usually dealing witha broadcast topology.

Can you imagine what the network

traffic overhead would be like on anetwork with 254 hosts trying todiscover each others MAC addresses?

Subnetting allows us to segment LANsinto logical broadcast domains calledsubnets, thereby improving networkperformance.


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Stealing /Borrowing Host Bits

In order to subnet, we must steal or borrowbits from the host portion on the IP address.

First, we must to determine how manysubnets we need and how many hosts per

subnet. We do this through the power of 2

For example, I need 8 subnets from a Class C: 24 = 16 - 2 = 14 subnets

Remember: we subtract 2 because these subnets are notused

How many host do we have? Its a Class C, so 4 bits are left: 24 = 16 - 2 = 14 hosts

Remember: we subtract 2 because one address is the

subnet address and one is the broadcast address


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Subnet Mask

We determine the subnet mask by adding upthe decimal value of the bits we borrowed.

In the previous Class C example, we borrowed4 bits. Below is the host octet showing the bits

we borrowed and their decimal values.

128 64 32 16 8 4 21

1 1 1 1

We add up the decimal value of these bits and get 240.Thats the last non-zero octet of our subnet mask.

So our subnet mask is 255.255.255.240


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Last Non-Zero Octet

Memorize this table. You should be able to: Quickly calculate the last non-zero octet when giventhe number of bits borrowed.

Determine the number of bits borrowed given thelast non-zero octet.

Determine the amount of bits left over for hosts andthe number of host addresses available.

Bits

Borrowed

Non-Zero

Octet Hosts

2 192 623 224 30

4 240 14

5 248 6

6 252 2


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CIDR Notation

Classless Interdomain Routing is a method ofrepresenting an IP address and its subnetmask with a prefix.

For example: 192.168.50.0/27

What do you think the 27 tells you? 27 is the number of 1 bits in the subnet mask.

Therefore, 255.255.255.224

Also, you know 192 is a Class C, so we borrowed 3

bits!! Finally, you know the magic number is 256 - 224 =32, so the first useable subnet address is197.168.50.32!!

Lets see the power of CIDR notation.


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202.151.37.0/26

Subnet mask? 255.255.255.192

Bits borrowed? Class C so 2 bits borrowed

Magic Number? 256 - 192 = 64

First useable subnet address? 202.151.37.64

Third useable subnet address? 64 + 64 + 64 = 192, so 202.151.37.192


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198.53.67.0/30

Subnet mask? 255.255.255.252

Bits borrowed? Class C so 6 bits borrowed

Magic Number? 256 - 252 = 4

Third useable subnet address? 4 + 4 + 4 = 12, so 198.53.67.12

Second subnets broadcast address? 4 + 4 + 4 - 1 = 11, so 198.53.67.11


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200.39.89.0/28

What kind of address is 200.39.89.32? Class C, so 4 bits borrowed

Last non-zero octet is 240

Magic number is 256 - 240 = 16

32 is a multiple of 16 so 200.39.89.32 is asubnet address--the second subnetaddress!!

Whats the broadcast address of200.39.89.32? 32 + 16 -1 = 47, so 200.39.89.47


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194.53.45.0/29

What kind of address is 194.53.45.26? Class C, so 5 bits borrowed Last non-zero octet is 248 Magic number is 256 - 248 = 8

Subnets are .8, .16, .24, .32, ect.

So 194.53.45.26 belongs to the third subnetaddress (194.53.45.24) and is a host address.

What broadcast address would this host use

to communicate with other devices on thesame subnet? It belongs to .24 and the next is .32, so 1 less is .31

(194.53.45.31)


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No Worksheet Needed!

After some practice, you should never need asubnetting worksheet again.

The only information you need is the IPaddress and the CIDR notation.

For example, the address 221.39.50/26

You can quickly determine that the firstsubnet address is 221.39.50.64. How?

Class C, 2 bits borrowed 256 - 192 = 64, so 221.39.50.64

For the rest of the addresses, just do multiplesof 64 (.64, .128, .192).


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The Key!!

MEMORIZE THIS TABLE!!! Or Know howto recreate/derive it!!!!

Bits

Borrowed

Non-Zero

Octet Hosts

2 192 62

3 224 30

4 240 14

5 248 66 252 2


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Practice On Your Own

Below are some practice problems. Take outa sheet of paper and calculate... Bits borrowed

Last non-zero octet

Second subnet address and broadcast address1. 192.168.15.0/26

2. 220.75.32.0/30

3. 200.39.79.0/29

4. 195.50.120.0/275. 202.139.67.0/28

1. Challenge: 132.59.0.0/19

2. Challenge: 64.0.0.0/16

Answers


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Answers

Address ClassBits

BorrowedLast Non-Zero Octet

SubnetJump

2nd Subnet'sAddress

2nd Subnet'sBroadcast

192.168.15.0/26 C 2 192 64 192.168.15.128 192.168.15.191

220.75.32.0/30 C 6 252 4 220.75.32.8 220.75.32.15

200.39.79.0/29 C 5 248 8 200.39.79.16 220.39.79.23195.50.120.0/27 C 3 224 32 195.50.120.64 195.50.120.95

202.139.67.0/28 C 4 240 16 202.139.67.32 202.139.67.47

132.59.0.0/19 B 3 224 32 132.59.64.0 132.59.95.255

64.0.0.0/16 A 8 255 1 64.2.0.0 64.2.255.255

Challenge:

Dont Cheat Yourself!! Work them out before you check your answers. Clickthe back button if youre not done. Otherwise, clickanywhere else in the screen to see the answers.

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Sub Netting - Apjohns0 Ch01-Where We'Ve Been