A: Parsing Layer and Header Terminology
I posted a question about headers and TCP/IP layers a few days back. Here are the answers! Post with any related clarifications or comments.
Answers: A, D
The TCP/IP model exists in two versions. One model uses four layers, with the lowest layer called Network Access or Network Interface. The alternate model uses the same upper layers, substituting two layers – the Data Link and Physical layers – for the Network Access layer.
The Ethernet header is generally associated with the data link layer, which matches the upper half of the network access layer. So, the terms Data Link and Network Access both apply when discussing Ethernet headers. Those facts rule in the two correct answers, and rule out the one incorrect answer that mentions layers.
The PDU acronym, Protocol Data Unit, refers to any header/trailer and its encapsulated data. That encapsulated data may include headers from other layers. For example, a layer 2 PDU (L2PDU) includes the layer 2 header and trailer, plus the encapsulated data. That encapsulated data, and often does, include a layer 3 header, layer 4 header, and so on.
However, a LxPDU does not include headers and trailers from lower layer headers. So, a layer 3 PDU (L3PDU) would include the layer 3 header, layer 4 header, and so on, but not the layer 2 header.
The term frame, listed in the question, refers to a layer 2 PDU. An Ethernet frame is therefore a layer 2 PDU that uses Ethernet framing, namely an Ethernet header and trailer.
All these facts about PDUs combine to rule out the other two incorrect answers. The Ethernet header, part of a Layer 2 PDU, is not part of any Layer 3 PDU. However, the Ethernet header in a layer 2 PDU is not the only header in the layer 2 PDU.