TCP/IPTCP/IP

• Why we should know this?

• Because we do not use any GUI (Wireshark)

when we are on a remote machine.

• We rely on CLI?

• A thorough and packet/bit -level knowledge

is required for packet / protocol analysis.

ANSWER THE QUESTIONS

• TCP/IP is multi-layered.

•Means - one functionality is running at one

layer and another functionality running at

another layer.

INTRODUCTION – TCP/IP

•Why this layered architecture?

• Extensible

•We can add new functionality to the layer

without having to re-implement the whole

TCP/IP stack code.

INTRODUCTION – TCP/IP

• There are two basic architectures to follow

when talking about layers.

• TCP/IP reference model

• OSI (Open Systems Interconnect) Reference

Model

INTRODUCTION – TCP/IP

INTRODUCTION – TCP/IP

• A packet originating from the source

computer traverse through the layers from top

layer to bottom.

• Each layer adds its own set of headers to the

packet.

• At the destination, the packets traverse from

bottom layer to the top layer.

HOW IT WORKS?

• At each layer, the headers are stripped out of

the packet.

• These header give the destination host all the

information needed to process the packet.

HOW IT WORKS?

OSI MODEL

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• Sending process passes data to the

application layer.

• The application layer attaches an application

header and then passes the frame to the next

layer (presentation layer) – known as

encapsulation.

LET’S GET SOME MORE DETAILS

• The process of adding headers is repeated

from layer to layer until the frame reaches the

data link layer.

• There, in addition to a data-link header, a

data-link trailer is added.

• The data-link trailer contains a checksum and

padding if needed.

LET’S GET SOME MORE DETAILS

•Why Checksum?

• For error detection

•Why padding?

• For frame synchronization

LET’S GET SOME MORE DETAILS

HEADER PAYLOAD TRAILER

A TCP PACKET

DATA DATA

T

C

P

I

P

F

R

A

M

E

T

R

A

I

L

E

R

• PDU = Protocol Data Unit

• Information that is delivered as a unit.

• Consists of layer's Header, Trailer and Data

encapsulated.

PDU

• Process of taking one Protocol Data Unit

(PDU) and enveloping it within a set of protocol

header and trailer.

ENCAPSULATION & PDU

• Each layer may add a Header and a Trailer to

its PDU as it proceeds through the layers.

• The Headers contain information that

specifically addresses layer-to-layer

communication

ENCAPSULATION & PDU

• Packet – PDU @ Layer 3 (Network Layer)

• Frame – PDU @ Layer 2 (Data Link)

ENCAPSULATION & PDU

PACKETS VS FRAMES

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