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IP Basics. IP. ICMP. Network. RoutingTables. ARP. Link. Physical. IP Basics. IP encapsulates TCP IP packets travel through many different routers (hops) before reaching it’s destination

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Ip basics

IP

ICMP

Network

RoutingTables

ARP

Link

Physical


Ip basics1
IP Basics

  • IP encapsulates TCP

  • IP packets travel through many different routers (hops) before reaching it’s destination

  • MTU variation at the physical layer requires IP to fragment the message into smaller units along the way

  • Reassembly is an option at each hop.

  • IP does NOT guarantee delivery!


Ip fragmentation
IP Fragmentation

1000 b

R

500 b

500 b

250 b

250 b

250 b

250 b

R

R

Every link has the potential to dictate adjusting size of frames.

It is possible to reassemble at any point.

1000 b

R

500 b

500 b

1000 b

R

R


What if frames are lost
What if frames are lost?

Receive

Computer

250 b

250 b

250 b

250 b

R

R

4

3

2

1

Receive computer will hold the first 2 frames awaiting the 3rd.

After a period of time, a timer expires and IP level passes the 500 bytes up and stops looking for the other pieces.

TCP (NOT IP) then will acknowledge receipt of 500 more bytes to the sending TCP layer. If the first frame is lost, NONE are passed up to TCP. More on TCP later.


Ip frame format fragmentation fields
IP Frame formatFragmentation Fields

Header

Length

Type of

Service

Packet Length

Version

32 bits

Each

line

Identification

Flags

Fragment Offset

Checksum

Time To Live

Protocol

Source IP Address

Destination IP Address

Options

DATA


Fragmentation and the frame fig 7 34
Fragmentation and the FrameFig 7.34

FragId 345

FragOffset=0

MoreFragments Bit=1

Size->1400 byes

FragId 345

FragOffset=175

MoreFragments Bit=1

Size-> 1400 bytes

4000 byte

frame

router

FragId 345

FragOffset=350

MoreFragments Bit=0

Size->1200 bytes

FragOffset should be multiplied by 8 (8x175=1400)


Ip frame format
IP Frame format

Header

Length

Type of

Service

Packet Length

Version

32 bits

Each

line

Identification

Flags

Fragment Offset

Checksum

Time To Live

Protocol

Source IP Address

Destination IP Address

Options

DATA


Ip summary
IP Summary

  • Fragmentation results in delivery of frames which are potentially smaller than the original transmission.

  • Some of the frames can be lost

  • If a message is fragmented and frames are lost, all frames up to the first lost frame are passed up to the receiving TCP and all subsequent frames are dropped.

  • TCP views this as a stream and is unaware of the loss of frames. It just accepts the next “n” bytes, acks the receipt, and waits for subsequent data.


Ip basics

TCP

End To End Delivery


Ip basics

Transport

TCP

UDP

Network

Link

Physical


Tcp basics
TCP basics

  • Connection-oriented

    • Sets up the connection prior to data transmission

      • SYN and 3-way handshake

    • Guarantees delivery of data

      • Sender holds a copy of the data for retransmission if necessary

      • Receiver ACKS specific byte positions in the stream so sender can resend from any byte position

  • Encapsulated by IP

  • Receiver tells sender it’s receive window size to limit rate of data arrival (flow control)



Tcp handling of fragmentation
TCP handling of fragmentation

Up to

destination port

(Send 2000 bytes)

Transport

Transport

(ACK 500 bytes)

2000

500

Network(IP)

Network(IP)

2501

2502

1000

2504

2503

1000

Network(IP)

Physical

Physical

Physical


Tcp handling of fragmentation1
TCP handling of fragmentation

Up to

destination port

(Send 2000 bytes)

Transport

Transport

(ACK 500 bytes)

2000

500

Network(IP)

Network(IP)

2501

2502

1000

2504

2503

1000

Network(IP)

Physical

Physical

Physical


Tcp handling of fragmentation2
TCP handling of fragmentation

Up to

destination port

(Send 2000 bytes)

Transport

Transport

(ACK 500 bytes)

2000

500

Network(IP)

Network(IP)

2501

2502

1000

2504

2503

1000

Network(IP)

Physical

Physical

Physical


Tcp handling of fragmentation3
TCP handling of fragmentation

Up to

destination port

(Send 2000 bytes)

Transport

Transport

(ACK 500 bytes)

2000

500

Network(IP)

Network(IP)

2501

2502

1000

2504

2503

1000

Network(IP)

Physical

Physical

Physical


What does the tcp frame look like
What does the TCP frame look like?

Data

Source Port

Destination Port

Length

Checksum


Ip basics

And after TCP is encapsulated in IP?

IP Header

IP Trailer

TCP



Tcp handshake setup
TCP handshake/setup

Host A

Host B

Ack 0, Syn 1

Ack 1, Syn 1

Ack 1, Syn 0

Ack 1, Syn 0

.

.

.

time

setup

data


Tcp frame
TCP Frame

Destination Port

Source Port

Sequence Number

Acknowledgment Number

HeaderLength

Flags

Window

Checksum

Urgent Pointer

Options

DATA


Flow control w tcp
Flow Control w/TCP

A

B

Data … s=101, a=701

Data … s=201, a=701

B says STOP

Data … s=701, a=301, c=0

B says GO

(up to 200)

Data … s=801, a=301, c=200

Data … s=301, a=901

Data … s=401, a=901



Udp basics
UDP basics

  • At transport layer as alternative to TCP

  • No connection establishment

  • No Guaranteed Delivery

  • Practically adds nothing to IP

  • Application must guarantee delivery if necessary

  • TCP and timing is hard for you to implement at the application layer

  • UDP runs faster if delivery is not required to be error-free.



Icmp basics

TCP/UDP

ICMP Basics

IP

ICMP

physical

  • Lower than IP

  • A support protocol for routing info/problems

  • Doesn’t use ports

  • Used in ping

  • Frequently used to deny service.. problematic

    • ping of death (too large message), and

    • denial of service (ping flood)


Icmp message types
ICMP Message types

  • Echo Request

  • Echo Response

  • Time Exceeded

  • Destination Unreachable

  • Redirect


Ip tunnelling
IP Tunnelling

Apple

talk

Apple

talk

Transport

Transport

(IP)

(IP)

Network(IP)

Physical

Physical

Physical

Intermediate

Routers only

See IP

Router

CAN do

AT in IP

Receiving

Router

Connected

Network

(AT)

Inside

Network

(AT)


Ip basics

IP Tunnelling at one end

Apple

talk

Transport

(IP)

Appletalk

Appletalk

AT

IP

Physical

Physical

Physical

AT

IP

Route to Destination

As IP

Appletalk to local

Appletalk to non-local