Ethernet Frames

It’s worth briefly looking at the frame structure of Ethernet. Why? Here are a couple of reasons:

  • Ethernet’s maximum frame size is 1,514 bytes.

  • Ethernet has several ways of encapsulating protocol data (TCP/IP, IPX/SPX, LAT, and so forth).

Ethernet’s maximum frame size includes six bytes for the MAC address of the source NIC, six bytes for the MAC address of the destination, a two-byte value indicating what kind of frame this is, and a “payload” portion that holds your data, such as a TCP/IP packet (this can be a maximum of 1,500 bytes). There are considerations and troubleshooting consequences for this maximum TCP/IP packet size (called the MTU or maximum transmission unit) of 1,500, but we’ll cover those in Hour 19.

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