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Networking Fundamentals · Foundational

Ethernet Frame

The Layer 2 unit Ethernet uses, containing destination MAC, source MAC, EtherType or length, payload and FCS.

Definition

An Ethernet II frame has a 6-byte destination MAC, 6-byte source MAC, 2-byte EtherType, a 46-1500 byte payload and a 4-byte FCS, for 64 to 1518 bytes total (1522 with an 802.1Q tag). A 7-byte preamble and 1-byte start frame delimiter precede it on the wire but are not counted in frame size. Frames below 64 bytes are runts.

Example

A frame with EtherType 0x0800 carries an IPv4 packet.

Exam tip

Minimum Ethernet frame is 64 bytes, maximum standard is 1518 bytes; destination MAC comes before source MAC.

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