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When reading through the Ethernet frame format in IEEE 802.3 , the EtherType was explained as below:

  1. 0 - 1500 (Decimal) comes under packet data payload length.
  2. 1536(0x600) and above it means the value is determining the type of the frame.(Eg. 0x800 stands for IPV4)

What about the values in between 1501 to 1535? Why these values been left off?

Note: On the Wiki link it is been mentioned it is not defined. But not finding as explanation in any standardized documents.

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These values are reserved to avoid ambiguity (e.g. when 802.1Q tagging is used, slightly increasing the frame size).

Using the Ethertype field for the frame length is obsolete though, Ethernet II framing (using the Ethertype field to indicate the protocol carried as payload) far outnumbers any other frame type. Instead, the length of the frame is indicated by carrier loss or a special end-of-frame symbol, depending on the PHY in use.

于 2018-05-22T20:51:09.573 回答