Does MTU include the preamble and Inter-Frame Gap IFG in Ethernet frames?

• A. Yes; MTU includes preamble and IFG
• B. No; MTU refers to the maximum frame size including headers but excluding preamble and IFG
• C. MTU excludes headers but includes payload
• D. MTU is only for wireless networks

Answer: (B)

MTU is the maximum size of the data unit that a network link can carry in a single frame. In Ethernet, a frame includes the MAC header, the payload, and the trailer (the FCS), but it does not include timing elements like the preamble (the 7-byte/8-byte sequence used for synchronization) or the Inter-Frame Gap (the 12-byte idle time between frames). So MTU refers to the largest frame size on the wire, counting the headers and trailer but excluding the preamble and IFG. For standard Ethernet, that maximum frame size is 1518 bytes (14-byte header + 1500-byte payload + 4-byte FCS). The common IPv4 MTU of 1500 bytes relates to the maximum IP payload that can fit inside that Ethernet frame’s payload, not to the preamble or IFG.