Network Building Blocks for Internet Communications
& The Vulnerabilities of Software Applications
Jacob Spiersch
INTL440 D001
Dr. Patrick Barton
March 26, 2022
1
Introduction
The internet communication system is highly technical but extremely powerful when it is
functioning properly. Users of this advanced infrastructure are able to communicate in mediums
of all kinds, including voice, text, and video, to endpoints all around the world with transmission
speeds faster than the blink of an eye. Our highly technical has become fully engrained in the
communication system that the internet provides. Today, many users have put much of their lives
onto the internet. Business models, financial instruments, sensitive personal information, and
medical records are just a few examples of the data that is being stored and transmitted on cyber
space networks.
Moving forward into this digital age of communication, it is important to understand the
ins and outs of how this complex system is functioning. Cyber attacks are on the rise. Criminal
activity within the cyberspace has been an issue since it’s inception in the 1970’s however,
according to a recent alert from the Cybersecurity & Infrastructure Security Agency, “United
States, Australia, and the United Kingdom observed an increase in sophisticated, high-impact
ransomware incidents against critical infrastructure organizations globally”.1 If we want to
continue enjoying the internet safely, we must take responsibility for the security of our own
sensitive information by educating ourselves on how this system works. In this essay, I will be
describing in detail how internet communication works by discussing the major network building
blocks and their functions.
1
United States. Cybersecurity and Infrastructure Security Agency. United States, 2022. Web Archive.
cisa.gov/uscert/ncas/alerts/aa22-040a
2
The OSI Model
The transmission of data over the internet must go through seven different stages or
“layers” if it is to be transmitted and received successfully. These seven layers are all part of the
Open Systems Interconnection (OSI) Model. The OSI model is sometimes referred to as the
reference model because it serves as a reference to how all network communications are being
executed.2 To fully grasp the concepts of internet communications, a basic understanding of how
these layers function in tandem with one another is crucial.
Layer 1 of the OSI model functions on the physical level. The binary ones and zeros
being electrically transmitted over a physical medium are referred to as “bits.” Activity present
over a physical wire like cat6 or fiber optics is portrayed as a one, and the absence of activity is
represented as a zero. This “activity” changes depending on the mode of transportation being
used. Cat5/6 and fiberoptics are just a few common examples of physical mediums use to
transport bits on the physical layer. All devices that receive and transmit bits through physical
mediums can be labeled as layer 1 physical devices.
The packaging and transmission of data into frames over the network is a function of
layer 2, or the Data Link Layer. Each individual device on a network is assigned a Media Access
Control (MAC) address that serves as its location, much in the same way a house has a mailing
address. A switch, being a layer 2 device, is not concerned with how devices are connected on
the physical level. Its job is to view networks logically by assigning packaged frames to the
proper MAC address. Layer 2 devices are also responsible for performing error
2
Dion, Jason. Section 3: OSI Model. In CompTIA Network+ (N10-007) Full Course & Practice Exam, edited
by Jason Dion for ComptTIA Network+ (N10-007). DionTraining.com, Winter 2021.
3
detection/correction which allows users to talk to one another without interfering with one
another.
The Network Layer (Layer 3) is concerned with routing. Routing is the forwarding of
traffic with logical addressing via internet protocols like IPv4 or IPv6. Switching is the process
in which data is divided into packets and forwarded to the requesting IP address. Packets are
forwarded from router to another until it reaches its final destination. Switching methods include
packet switching, circuit switching and message switching. Depending on the method being
used, the route may be different, but the idea is that the packet gets to the proper assigned IP
address in the end. Once the packets have been transmitted successfully, it becomes the job of
switches on layer 2 to distribute this information to the correct device.
Layer 4 is the transmission of segments on the Transport Layer. The two transmission
protocols in layer 4 are TCP (Transmission Control Protocol) and UDP (User Datagram
Protocol). TCP uses a series of synchronizations and acknowledgments to ensure the data is
being transmitted completely and successfully3. This is referred to as a 3-way handshake and is
most often used when transmitting important information like banking and medical information.
UDP is faster than TCP because it does not require a handshake before data transmission can
occur. UDP is commonly used to transmit audio and video due to the constant stream of
information being sent. TCP’s strict transmission style would cause constant streams of
information to seize up and lag if the connection were not flawless. In Layer 4 we are concerned
with how the information is being sent whereas Layer 3 takes care of the location via routing and
IP protocols.
3
Charles M Kozierok, The TCP/IP Guide: a Comprehensive, Illustrated Internet (San Francisco, CA: No
Startch Press, 2005)
4
The Session Layer (Layer5) is responsible for session management. Session management
includes various parameters such as opening, closing, checkpointing and the synchronization of
information sources. Layer 5 calls upon the information provided by TCP segment header in
layer 4 to further send data to layer 6, also known as the Presentation Layer. At layer 6, the
formatting and representation of data takes place.4 This enables two different devices to
communicate clearly with one another even if the programming language differs between the
two end points. This is also where encryption and compression take place before moving on to
the Application Layer.
The Application Layer of the OSI model is the 7th and final layer, making it the layer
closest to the user. Low-level application services like email protocol and file transfer protocol
fall under this category. This is not to be confused with bigger 3rd party applications like Google
Chrome or Microsoft Word. Bigger apps that users are familiar with work atop these low-level
app services for a smooth and seamless experience. Layer 7 is also where service advertisement
takes place which makes it easier to categorize, find, and implement devices with out having to
manually connect them.
Application and Web Browser Vulnerabilities
With this basic understanding of the OSI model for which all internet communications
are built upon, we can now discuss the vulnerabilities of software applications such as those
found in web browsers. It is important to put emphasis on this because this is where most users
go for their information. The high level of user traffic moving through these web browsers is
4
James Edwards and Richard Bramante, Networking Self-Teaching Guide: OSI, TCP/IP, Lans, Mans, Wans,
Implementation, Management, and Maintenance (Indianapolis, IN: Wiley Pub., 2009).
5
what attracts a cyber criminal to the space. If users would like to be remain unbothered from
these criminals, awareness of such vulnerabilities is essential.
Web browser application developers work tirelessly to provide users with the latest and
greatest products to enhance their services and retain their customers. New browser features
being pushed out usually provide to the user increased workflow capabilities and extra utility
control to make their work easier and more efficient. Features like browser plug-ins, cookies, and
ActiveX do provide many useful features, however, they most of the time come with settings and
parameters, that if not set correctly could put you at risk for an attack. This constant evolution of
applications and services allows malware authors to hide behind and exploit newly developed
software.
Additionally, web browser applications are extremely accessible and easy to use. This
level of flexibility and ease of use is great, but it’s also what makes web browsers such a
dangerous place. Browsers are designed to allow customizable search functions which allow
users to virtually unlimited web pages. Malware authors take advantage of this by planting
malicious web pages in the guise of familiar and credible developers to entice their victims.5
These vulnerabilities are just a few examples of how dangerous applications and web browsers
can be to the unsuspecting user.
Conclusion
The network building blocks built atop the OSI model have provided to us the most
efficient form of communication the world has ever seen. This platform has been around for over
5
United States. Cybersecurity and Infrastructure Security Agency. United States, 2022. Web Archive.
cisa.gov/uscert/publications/securing-your-web-browser
6
half a century, and its use is growing exponentially. New products and features being released to
the masses daily opens the door for criminal exploitation and malicious attacks to
personal/sensitive information. With a basic understanding of how internet communications
function, combined with the awareness of dangers that may come with consumer application
services, users become better equipped to defend themselves from the fast-evolving malicious
territory of cyberspace.
7
Bibliography
“Alert (AA22-040A).” CISA. Cybersecurity & Infrastructure Security Agency, February 9,
2022. https://www.cisa.gov/uscert/ncas/alerts/aa22-040a.
Dion, Jason. “Section 3: OSI Model.” Open Systems Interconnection (OSI) Model Overview.
Lecture presented at the CompTIA Network+ (N10-007) Full Course & Practice
Exam, February 25, 2022.
Kozierok, Charles M. The TCP/IP Guide : a Comprehensive, Illustrated Internet Protocols
Reference. 1st ed. San Francisco: No Starch Press, 2005.
Edwards, James, and Richard Bramante. Networking Self-Teaching Guide: OSI, TCP/IP, Lans,
Mans, Wans, Implementation, Management, and Maintenance. Indianapolis, IN: Wiley
Pub., 2009.
“Securing Your Web Browser.” CISA. Cybersecurity & Infrastructure Security Agency.
Accessed March 26, 2022. https://www.cisa.gov/uscert/publications/securing-your-webbrowser.
8