MAC Address Length in Ethernet | Generated by AI
Question: In the IEEE 802.3 MAC frame structure, there are two addresses: the source address and the destination address. Both of these addresses are how many bits long?
A. 16-bit
B. 32-bit
C. 48-bit
D. 96-bit
Answer:
C. 48-bit
Detailed explanation:
In the IEEE 802.3 standard (Ethernet), the MAC frame format includes the following main fields in order:
- Preamble (7 bytes) + Start Frame Delimiter (SFD) (1 byte)
- Destination MAC Address — 6 bytes (48 bits)
- Source MAC Address — 6 bytes (48 bits)
- Length/Type field — 2 bytes
- Data (payload) — 46–1500 bytes (padded if necessary)
- Frame Check Sequence (FCS) — 4 bytes
Both the destination address and source address fields are fixed at 6 bytes, which equals 48 bits.
These 48-bit addresses are commonly called MAC addresses (Media Access Control addresses). They are globally unique hardware addresses assigned to network interface controllers (NICs), usually expressed in hexadecimal format (e.g., 00:1A:2B:3C:4D:5E).
Why not the other options?
- A. 16-bit: Too short — used in some older or specialized protocols, not Ethernet
- B. 32-bit: Matches IP addresses (IPv4), but MAC addresses are always 48 bits in Ethernet
- D. 96-bit: No standard Ethernet MAC frame uses 96-bit addresses
Your answer (C) was correct.
References:
- None (standard IEEE 802.3 / Ethernet specification knowledge)