13 tcpip and osi

8/2/2019 13 Tcpip and Osi

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TCP/IP & OSI

In OSI reference model terminology -theTCP/IP protocol suite covers the networkand transport layers.

TCP/IP can be used on many data-linklayers (can support many networkhardware implementations).


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Early protocol suite

Universal

Introduction to TCP/IPHost

Internet

TCP/IP

Host

Router Router


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TCP/IP Protocol Stack

7

6

5

4

3

2

5

4

3

2

Application

Presentation

Session

Transport

Network

Data Link

Physical1

Application

Transport

Internet

Data Link

Physical

1

OSI DOD


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Application Layer Overview

Application

Transport

Internet

Data Link

Physical

File Transfer- TFTP- FTP- NFS

E-Mail- SMTP

Remote Login- Telnet- rlogin

Network Management- SNMP

Name Management- DNS


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Transport Layer Overview

Transmission ControlProtocol (TCP)

User DatagramProtocol (UDP)

Application

Transport

Internet

Data Link

Physical

Connection-Oriented

Connectionless


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TCP Segment Format

Source port (16) Destination port (16)

Sequence number (32)

Headerlength (4)

Acknowledgement number (32)

Reserved (6) Code bits (6) Window (16)

Checksum (16) Urgent (16)

Options (0 or 32 if any)

Data (varies)

20Bytes

Bit 0 Bit 15 Bit 16 Bit 31


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Port Numbers

TCP

Port

Numbers

FTP

TransportLayer

TELNET

DNS

SNMP

TFTP

SMTP

UDP

ApplicationLayer

21 23 25 53 69 161

RIP

520


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TCP Port Numbers

SourcePort

Dest.Port

Host A

1028 23

SP DP

Host ZTelnet Z

Dest. port = 23.

Send packet to my

Telnet

application.


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Send SYN(seq=100 ctl=SYN)

SYN received

Host A Host B

TCP Three Way

Handshake/Open Connection

1


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SYN received

Send SYN, ACK(seq=300 ack=101 ctl=syn,ack)

Host A Host B

SYN received

1

2

TCP Three Way Handshake/Open

Connection


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SYN received

Send SYN, ACK(seq=300 ack=101 ctl=syn,ack)

Established

(seq=101 ack=301 ctl=ack)

Host A Host B

1

2

3

SYN received

TCP Three Way Handshake/OpenConnection


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TCP Simple Acknowledgment

Window size = 1

Sender Receiver


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Window size = 1

Sender Receiver

Send 1Receive 1


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Window size = 1

Sender Receiver

Send 1Receive 1

Receive ACK 2Send ACK 2


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Window size = 1

Sender Receiver

Send 1Receive 1


Send 2Receive 2


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Window size = 1

Sender Receiver

Send 1Receive 1


Send 2Receive 2



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Window size = 1

Sender Receiver

Send 1Receive 1


Send 2Receive 2


Send 3 Receive 3


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Window size = 1

Sender Receiver

Send 1Receive 1


Send 2Receive 2


Send 3 Receive 3

Receive ACK 4 Send ACK 4



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TCP Sequence and

Acknowledgment Numbers

SourcePort

Dest.Port

Sequence#

Acknowledgement#

Source Dest. Seq. Ack.

1028 23 10 1

I just

sent #10.


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TCP Sequence and

Acknowledgment Numbers

I just got #10,now I need #11.

SourcePort

Dest.Port

Sequence

#Acknowledgement

#

1028 23

Source Dest.

10

Seq.

1

Ack.

102823Source Dest.

11Seq.

1Ack.

I just

sent #10.


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TCP Sequence and

Acknowledgment NumbersSource

PortDest.Port

Sequence

#Acknowledgement

#

1028 23

Source Dest.

11

Seq.

2

Ack.

1028 23

Source Dest.

10

Seq.

1

Ack.

102823Source Dest.

11Seq.

1Ack.


I just

sent #11.


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TCP Sequence and

Acknowledgment NumbersSource

PortDest.Port

Sequence

#Acknowledgement

#

1028 23

Source Dest.

11

Seq.

101

Ack.

1028 23

Source Dest.

10

Seq.

100

Ack.

102823Source Dest.

11Seq.100

Ack.

102823

Source Dest.

12

Seq.

101

Ack.


I just

sent #11.


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TCP Windowing

Sender Receiver


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TCP Windowing

Window size = 3

Send 2

Sender ReceiverWindow size = 3Send 1

Window size = 3Send 3


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Window size = 3

Send 2

TCP Windowing

Sender Window size = 3Send 1


ACK 3Window size = 2

Packet 3 isDropped

Receiver


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Window size = 3

Send 2

TCP Windowing




Packet 3 isDropped



Receiver


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Window size = 3

Send 2

TCP Windowing




Packet 3 isDropped




ReceiverWindow size = 3


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UDP

DatagramDelivery

Connectionless Unreliable

Minimal


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No sequence or acknowledgment fields

UDP Segment Format

Source port (16) Destination port (16)

Length (16)

Data (if any)

1Bit 0 Bit 15 Bit 16 Bit 31

Checksum (16)

8Bytes


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Internet Layer Overview

OSI network layer corresponds to theTCP/IP internet layer

Internet Protocol (IP)

Internet Control MessageProtocol (ICMP)

Address ResolutionProtocol (ARP)

Reverse AddressResolution Protocol (RARP)

Application

Transport

Internet

Data Link

Physical


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IP Datagram

Version(4)

Destination IP Address (32)

Options (0 or 32 if any)

Data (varies if any)

1Bit 0 Bit 15 Bit 16 Bit 31

HeaderLength (4)

Priority & Typeof Service (8)

Total Length (16)

Identification (16)Flags

(3) Fragment offset (13)

Time to live (8) Protocol (8) Header checksum (16)

Source IP Address (32)

20Bytes


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Determines destination upper-layer protocol

Protocol Field

TransportLayer

InternetLayer

TCP UDP

ProtocolNumbers

IP

176


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Internet Control Message

Protocol

Application

Transport

Internet

Data Link

Physical

Destination

Unreachable

Echo (Ping)

Other

ICMP

1


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Address Resolution Protocol

172.16.3.1 172.16.3.2

IP: 172.16.3.2 = ???

I need the

Ethernet

address of

176.16.3.2.


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172.16.3.1 172.16.3.2

IP: 172.16.3.2 = ???

I heard that broadcast.

The message is for me.

Here is my Ethernet

address.

I need the

Ethernet

address of

176.16.3.2.


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172.16.3.1

IP: 172.16.3.2Ethernet: 0800.0020.1111

172.16.3.2

IP: 172.16.3.2 = ???



Here is my Ethernet

address.

I need the

Ethernet

address of

176.16.3.2.


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Map IP MAC

Local ARP

172.16.3.1

IP: 172.16.3.2Ethernet: 0800.0020.1111

172.16.3.2

IP: 172.16.3.2 = ???



Here is my Ethernet

address.

I need the

Ethernet

address of

176.16.3.2.


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Reverse ARP

Ethernet: 0800.0020.1111 IP = ???

What is

my IP

address?


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Reverse ARP

Ethernet: 0800.0020.1111 IP = ???

What is

my IP

address?

I heard that

broadcast.

Your IP

address is

172.16.3.25.


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Reverse ARP

Ethernet: 0800.0020.1111IP: 172.16.3.25

Ethernet: 0800.0020.1111 IP = ???

What is

my IP

address?

I heard that

broadcast.

Your IP

address is

172.16.3.25.


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Reverse ARP

Map MAC IP

Ethernet: 0800.0020.1111IP: 172.16.3.25

Ethernet: 0800.0020.1111 IP = ???

What is

my IP

address?

I heard that

broadcast.

Your IP

address is

172.16.3.25.


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Unique addressing allows communicationbetween end stations

Path choice is based on destination address

Location is represented by an address

Introduction to TCP/IP Addresses

172.18.0.2

172.18.0.1

172.17.0.2172.17.0.1

172.16.0.2

172.16.0.1

SA DAHDR DATA10.13.0.0 192.168.1.0

10.13.0.1 192.168.1.1


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Internet Protocol

The IP in TCP/IP IP is the network layer

packet delivery service (host-to-host).

translation between different data-linkprotocols.


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IP Datagrams

IP provides connectionless, unreliabledelivery of IP datagram.

Connectionless: each datagram isindependent of all others.

Unreliable:there is no guarantee thatdatagrams are delivered correctly or at all.


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IP Addresses

IP addresses are not thesame as the underlyingdata-link (MAC) addresses.


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IP Addresses

IP is a network layer - it must be capableof providing communication between hostson different kinds of networks (different

data-link implementations).

The address must include informationabout what networkthe receiving host is

on. This makes routing feasible.


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IP Addresses

IP addresses are logicaladdresses (notphysical)

32 bits. Includes a network ID and a host ID.

Every host must have a unique IP address.

IP addresses are assigned by a centralauthority (the NIC/IANA).


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Format of IP address

bbbbbbbb bbbbbbbb bbbbbbbb bbbbbbbb


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The fourformats of IP Addresses

0NetID

10

110 NetID

1110 Multicast Address

HostID

NetID HostID

HostID

ClassA

B

C

D

8 bits 8 bits 8 bits8 bits


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Class A

128 possible network IDs over 4 million host IDs per networkID

Class B

16K possible network IDs

64K host IDs per network ID

Class C over 2 million possible network IDs

about 256 host IDs per network ID


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Network and Host IDs

A Network ID is assigned to anorganization by a global authority.

Host IDs are assigned locally by a systemadministrator.

Both the Network ID and the Host ID areused for routing.


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IP Addresses

IP Addresses are usually shown in dotteddecimalnotation:

1.2.3.4 00000001 00000010 00000011 00000100

128.213.1.110000000 11010101 00000001 00000001

This has a class B network


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Host and Network Addresses

A single network interface is assigned asingle IP address called the hostaddress.

A host may have multiple interfaces, andtherefore multiple hostaddresses.

Hosts that share a network all have thesame IP networkaddress (the network ID).


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IP Broadcast and Network

Addresses

An IP broadcast addresses has a host ID ofall 1s.

IP broadcasting is not necessarily a truebroadcast, it relies on the underlyinghardware technology.

An IP address that has a host ID of all 0s iscalled a network addressand refers to anentire network.


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Subnet Addresses

An organization can subdivide its host

address space into groups called subnets.

The subnet ID is generally used to grouphosts based on the physical networktopology.

10 NetID SubnetID HostID


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Subnetting

router

Subnet 1128.213.1.x

Subnet 2128.213.2.x

Subnet 3128.213.3.x


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Subnetting

Subnets can simplify routing.

IP subnet broadcasts have a hostID of all1s.

It is possible to have a single wire networkwith multiple subnets.


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Mapping IP Addresses to Hardware

Addresses IP Addresses are not recognized by

hardware.

If we know the IP address of a host, howdo we find out the hardware address ?

The process of finding the hardwareaddress of a host given the IP address iscalled

Address Resolution


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Reverse Address Resolution

The process of finding out the IP addressof a host given a hardware address iscalled

Reverse Address Resolution

Reverse address resolution is needed bydiskless workstations when booting.


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ARP

The Address Resolution Protocolis usedby a sending host when it knows the IPaddress of the destination but needs the

Ethernet address.

ARP is a broadcast protocol - every hoston the network receives the request.

Each host checks the request against its

IP address - the right one responds.


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ARP

ARP does not need to be done every timean IP datagram is sent - hosts rememberthe hardware addresses of each other.

Part of the ARP protocol specifies that thereceiving host should also remember theIP and hardware addresses of the sending

host.


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ARP

HEY - Everyone please listen! Will 128.213.1.5please send me his/her Ethernet address

not me

Hi Red! Im 128.213.1.5, and my Ethernet

address is 87:A2:15:35:02:C3


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RARP

HEY - Everyone please listen!My Ethernet address is22:BC:66:17:01:75.

Does anyone know my IP address ?

not me

Hi Red ! Your IP address is 128.213.1.17.


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Services provided by IP

Connectionless Delivery (each datagramis treated individually).

Unreliable (delivery is not guaranteed).

Fragmentation / Reassembly (based onhardware MTU).

Routing.

Error detection.


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IP Datagram

VERS HL

Fragment Offset

Fragment LengthService

Datagram ID FLAG

TTL Protocol Header Checksum

Source Address

Destination Address

Options (if any)

Data

1 byte1 byte 1 byte 1 byte


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IP Datagram Fragmentation

Each fragment (packet) has the samestructure as the IP datagram.

IP specifies that datagram reassembly isdone only at the destination (not on a hop-by-hop basis).

If any of the fragments are lost - the entire

datagram is discarded (and an ICMPmessage is sent to the sender).


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IP Datagram Fragmentation

If packets arrive too fast - the receiverdiscards excessive packets and sends anICMP message to the sender (SOURCE

QUENCH).

If an error is found (header checksumproblem) the packet is discarded and an

ICMP message is sent to the sender.

ICMP


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ICMPInternet Control Message Protocol

ICMP is a protocol used for exchangingcontrol messages.

ICMP uses IP to deliver messages.

ICMP messages are usually generatedand processed by the IP software, not theuser process.


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ICMP Message Types

Echo Request

Echo Response

Destination Unreachable Redirect

Time Exceeded

Redirect (route change) there are more ...


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TCP UDP

IP

Hardware

Process Layer

Transport Layer

Network Layer

Data-Link Layer

Process Process

ICMP, ARP

&

RARP


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Network Services

Support Any LAN & WAN architecture

Ethernet, Token Ring, ATM, Frame-Relay,X.25 etc


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TCP/IP Summary

IP: network layer protocol

unreliable datagram delivery between hosts.

UDP: transport layer protocol unreliable datagram delivery between

processes.

TCP: transport layer protocol

reliable, byte-stream delivery betweenprocesses.

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