In standard Ethernet, which set of fields belongs to the data link layer portion of a frame header and trailer?

Introduction / Context:
Ethernet frames are the fundamental units of data at the data link layer on most local area networks. Understanding which fields belong to the Ethernet frame header and trailer helps learners distinguish between layer 2 and higher layer information and correctly interpret packet captures and network diagrams.

Given Data / Assumptions:

• We are dealing with standard Ethernet framing as defined for IEEE 802.3.
• We focus on the fields used at the data link layer, not the network or transport layers.
• The question asks which group of fields makes up the relevant portion of the Ethernet frame that carries user data and error checking information.
• Higher layer fields such as IP addresses and port numbers are not part of the data link layer frame header or trailer.

Concept / Approach:
An Ethernet frame at the data link layer typically includes the destination MAC address, source MAC address, an optional 802.1Q tag, a Length or Type field, the payload data, and a Frame Check Sequence for error detection. The MAC addresses identify the sending and receiving network interfaces on the local link, while the Length or Type field tells the receiver what protocol is encapsulated, such as IPv4 or IPv6. The FCS provides a cyclic redundancy check to detect transmission errors. IP addresses and transport layer ports are encapsulated inside this payload and belong to higher layers.

Step-by-Step Solution:
1. Recall the structure of an Ethernet frame: destination MAC, source MAC, Length/Type, data, and FCS.2. Option A lists exactly these fields, describing a complete data link layer frame header, payload, and trailer.3. Option B contains Source IP, Destination IP, and TCP port, which belong to network and transport layers.4. Option C mixes preamble and start-of-frame delimiter with Source IP, but the IP field is not part of the data link header.5. Option D describes a mix of VLAN ID and higher layer fields, which does not match the core Ethernet data link structure described in the question.

Verification / Alternative check:
Network references and protocol analyzers such as Wireshark show the Ethernet frame header fields clearly separated from encapsulated IP and TCP or UDP headers. Inspecting real traffic confirms that the data link layer fields include MAC addresses, Length/Type, payload, and FCS, matching option A.

Why Other Options Are Wrong:
Option B focuses entirely on layer 3 and layer 4 information, which sits inside the Ethernet payload, not in the Ethernet frame header or trailer. Option C introduces IP information into what should be purely layer 2, and the combination listed is not the canonical Ethernet frame layout. Option D includes VLAN ID and transport layer details but omits the essential MAC and FCS fields defined for the data link layer.

Common Pitfalls:
It is easy to confuse the layered model when reading packet captures, because tools display all headers together. Students sometimes think that IP addresses or port numbers are part of the Ethernet frame itself rather than payload data. Remember that the data link layer is concerned with local delivery on a single link, using MAC addresses and FCS, while IP and TCP or UDP operate at higher layers.

Final Answer:
Destination MAC, Source MAC, Length/Type, Data, Frame Check Sequence (FCS)