What is the total size of an Ethernet header and trailer, excluding the Preamble and SFD?

The total size of an Ethernet header and trailer, excluding the Preamble and Start Frame Delimiter (SFD), is indeed 18 bytes.

In an Ethernet frame, the header consists of several important fields: the destination MAC address (6 bytes), the source MAC address (6 bytes), and the Ethertype or Length field (2 bytes). This totals to 14 bytes for the header.

The trailer usually comprises the Frame Check Sequence (FCS), which is 4 bytes in length. When you add the size of the header (14 bytes) and the trailer (4 bytes), you arrive at a total of 18 bytes. This is why the correct answer is reflective of the actual size of the Ethernet frame components outside the Preamble and SFD, which are not typically counted in this total.