What Are the Three Parts of All Layer 2 Frames? (Choose Three.)

Preparing for the Cisco 200-301 exam requires thorough practice, and using Cisco 200-301 practice tests is one of the most effective ways to ensure success. These practice tests simulate the real exam environment, helping candidates familiarize themselves with the question format, time constraints, and key topics such as networking fundamentals, IP services, security, and automation.

Tech Professionals

04 April 2025

Cisco

What Are the Three Parts of All Layer 2 Frames? (Choose Three.)

Introduction To Cisco 200-301 Practice Test

If you're preparing for the Cisco 200-301 exam, understanding Layer 2 frames is crucial. The CCNA 200-301 certification validates your knowledge of networking fundamentals, including how data is transmitted across networks. One of the key concepts you must master is the structure of Layer 2 frames, which are fundamental to Ethernet communication.

In this blog, we’ll break down the three essential parts of all Layer 2 frames—information that is often tested in the Cisco 200-301 Practice Test. Whether you're studying for your exam or looking to strengthen your networking knowledge, this guide will help you grasp these core concepts.

For the best preparation, check out Study4Pass, a trusted resource for Cisco 200-301 practice tests and study materials.

Understanding Layer 2 in the OSI Model

Before diving into the components of a Layer 2 frame, let’s briefly recap the OSI (Open Systems Interconnection) model, which divides network communication into seven layers:

1. Physical Layer (Layer 1) – Deals with raw bit transmission over cables or wireless signals.

2. Data Link Layer (Layer 2) – Responsible for node-to-node data transfer and error detection.

3. Network Layer (Layer 3) – Handles logical addressing and routing (IP addresses).

4. Transport Layer (Layer 4) – Ensures end-to-end communication (TCP/UDP).

5. Session Layer (Layer 5) – Manages connections between applications.

6. Presentation Layer (Layer 6) – Translates data into a readable format (encryption, compression).

7. Application Layer (Layer 7) – Interfaces directly with user applications (HTTP, FTP).

Layer 2 (Data Link Layer) is where frames are constructed and transmitted between devices on the same network.

The Three Essential Parts of a Layer 2 Frame

All Layer 2 frames consist of three main components:

1. Header

2. Payload (Data)

3. Trailer

Let’s explore each part in detail.

1. Frame Header

The header contains crucial control information needed for frame delivery. It typically includes:

Destination MAC Address (6 bytes) – Identifies the intended recipient.
Source MAC Address (6 bytes) – Identifies the sender.
EtherType (2 bytes) – Specifies the protocol encapsulated in the payload (e.g., IPv4, IPv6, ARP).
Some frames (like IEEE 802.3 Ethernet) may also include:
VLAN Tag (4 bytes) – Used for Virtual LAN identification (optional).

Why is the Header Important?

Ensures the frame reaches the correct device.
Helps switches forward frames efficiently.

2. Payload (Data)

The payload is the actual data being cisco 200-301 Certification transmitted. It contains:

Encapsulated Layer 3 packet (IP packet) – Typically an IPv4 or IPv6 packet.
Maximum Transmission Unit (MTU) – Usually 1500 bytes for Ethernet, but can vary.

Why is the Payload Important?

Carries the user data (e.g., web pages, emails, files).
Must be correctly encapsulated for proper delivery.

3. Frame Trailer

The trailer is used for error detection and marks the end of the frame. It includes:

Frame Check Sequence (FCS) (4 bytes) – A CRC (Cyclic Redundancy Check) value to detect corruption.

Why is the Trailer Important?

Ensures data integrity by detecting transmission errors.
If the FCS fails, the frame is discarded.
Visual Representation of a Layer 2 Frame

Here’s a simplified structure of an Ethernet frame:

Component	Size (Bytes)	Description
Destination MAC	6	Recipient’s hardware address.
Source MAC	6	Sender’s hardware address.
EtherType	2	Indicates the payload protocol.
Payload (Data)	46–1500	Contains the Layer 3 packet.
FCS (Trailer)	4	Error-checking (CRC).

Common Layer 2 Frame Types

Different networking standards use slightly different frame formats. The most common are:

1. Ethernet II (DIX) – Most widely used in modern networks.

2. IEEE 802.3 (Original Ethernet) – Used in older networks.

3. IEEE 802.1Q (VLAN Tagged Frame) – Adds a VLAN identifier.

Understanding these variations is essential for the Cisco 200-301 exam.

How This Topic Appears in the Cisco 200-301 Exam

The CCNA 200-301 exam often tests your knowledge of Layer 2 frames with questions like:

What are the three parts of all Layer 2 frames?

Answer: Header, Payload, Trailer

Which field in an Ethernet frame is used for error detection?

Answer: FCS (Frame Check Sequence)

What is the purpose of the EtherType field?

Answer: To identify the encapsulated protocol (e.g., IPv4, IPv6).

To practice such questions, use Study4Pass’s Cisco 200-301 practice test, which includes real exam-like scenarios.

Why Mastering Layer 2 Frames Matters for Network Engineers

1. Troubleshooting Connectivity Issues – If frames are corrupted, the FCS helps identify errors.

2. Optimizing Network Performance – Understanding MTU sizes prevents fragmentation.

3. Security Analysis – Inspecting frame headers helps detect MAC spoofing attacks.

Final Tips for CCNA 200-301 Exam Success

1. Use Reliable Study Resources – Study4Pass offers high-quality Cisco 200-301 practice tests to reinforce your knowledge.

2. Practice with Packet Tracer/Wireshark – Analyze real frame structures.

3. Review Key Concepts Regularly – Layer 2 framing is a fundamental topic.

Conclusion

Understanding the three parts of a Layer 2 frame (Header, Payload, Trailer) is essential for anyone pursuing the Cisco CCNA 200-301 certification. These components ensure reliable data transmission across networks.