CEH

Working with the Open Systems Interconnection Model 31

The OSI model, shown in the left side of Figure 2.6, has seven layers. As you read
through each layer’s function, keep in mind that we are working our way through how data
flows. Each layer is connected to the next; this concept will prove valuable as a reference for
more advanced data analysis.

You may already have some experience with the OSI model, or none at

all. If you are in the latter group you may have avoided learning the model

because it is complex. But you must learn it, because it is essential to fur-

thering your career—and to passing the exam.

FigurE 2.6 OSI TCP/IP comparative model

Application Layer

Application

Layer

Host-to-Host Transport

Internet Layer

Network Interface

Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

The CEH exam will focus on your understanding of the OSI model as it

applies to specific attacks. General knowledge of the model and the stages

of traffic flow within it will help you figure out what each question is

asking.

Layer 1: Physical The physical layer consists of the physical media and dumb devices that
make up the infrastructure of our networks. This pertains to the cabling and connections
such as Category 5e and RJ-45 connectors. Note that this layer also includes light and rays,
which pertain to media such as fiber optics and microwave transmission equipment. Attack
considerations are aligned with the physical security of site resources. Although not flashy,
physical security still bears much fruit in penetration (pen) testing and real-world scenarios.