Open Systems Interconnection (OSI) Layers One to Four: Physical, Data Link, Network and Transport

IntermediateFree5 modules · 15 lessons · ~2 min

About this course

A practical, honest treatment of the bottom four Open Systems Interconnection (OSI) layers for platform and infrastructure engineers. You will work through cabling and radio media, Media Access Control (MAC) addressing and switching, Virtual Local Area Networks (VLANs), the Address Resolution Protocol (ARP), Internet Protocol (IP) routing, and the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). The course closes with where Transport Layer Security (TLS) actually sits above transport and a clear statement of what each layer can and cannot protect.

What you'll learn

The Physical Layer

Physical Layer Fundamentals: Cabling, Radio and Signals
Physical Layer Security: Tapping, Jamming and Access Control

The Data Link Layer

Ethernet Frames and Media Access Control Addressing
Switching, Virtual Local Area Networks and the Address Resolution Protocol
Data Link Attacks and Defences

The Network Layer

Internet Protocol Addressing and Routing Fundamentals
The Internet Protocol Header and a Traceroute Read
Network Layer Security: Access Control Lists, Firewalls and Segmentation

The Transport Layer

Transmission Control Protocol (TCP) Mechanics and the Three-Way Handshake

01The Physical Layer2 lessons

Physical Layer Fundamentals: Cabling, Radio and Signals
Physical Layer Security: Tapping, Jamming and Access Control

02The Data Link Layer3 lessons

Ethernet Frames and Media Access Control Addressing

Common questions

How much does Safeguard Academy cost?

Nothing. Every course, exam, and certificate on the catalog is free — including retakes. All you need is a free Safeguard account.

What are the prerequisites?

None. The flagship course, Safeguard Certified Practitioner, is a beginner-level course — basic familiarity with how software is built helps, but every exam question is answerable from the lessons themselves.

User Datagram Protocol (UDP) and When Connectionless Transport Is the Right Choice

Transport Layer Exposure: Open Ports, SYN Floods, and Why Confidentiality Lives Above This Layer

Reading, Triage and Synthesis

Reading a Packet Capture: Frame, Internet Protocol Header and Transmission Control Protocol Header as One Story
Worked Triage Across Layers One to Four
Encapsulation and Decapsulation, Layer by Layer
What to Instrument and Monitor at Each Layer, and a Forward Look Beyond Layer Four

Switching, Virtual Local Area Networks and the Address Resolution Protocol

Data Link Attacks and Defences

03The Network Layer3 lessons

Internet Protocol Addressing and Routing Fundamentals
The Internet Protocol Header and a Traceroute Read
Network Layer Security: Access Control Lists, Firewalls and Segmentation

04The Transport Layer3 lessons

Transmission Control Protocol (TCP) Mechanics and the Three-Way Handshake
User Datagram Protocol (UDP) and When Connectionless Transport Is the Right Choice
Transport Layer Exposure: Open Ports, SYN Floods, and Why Confidentiality Lives Above This Layer

05Reading, Triage and Synthesis4 lessons

Reading a Packet Capture: Frame, Internet Protocol Header and Transmission Control Protocol Header as One Story
Worked Triage Across Layers One to Four
Encapsulation and Decapsulation, Layer by Layer
What to Instrument and Monitor at Each Layer, and a Forward Look Beyond Layer Four2 min

What happens if I fail the exam?

You can retake it after a 24-hour cooldown, as many times as you need. Retakes are free, and each attempt draws a fresh random set of questions.

How long is a certificate valid?

The Safeguard Certified Practitioner credential is valid for 24 months from issue. The expiry date is printed on the certificate and shown live on its public verification page. Renewing means passing the current exam again.