EtherType

EtherType is a field of a screen Ethernet indicating which is the protocol of higher level used in the field " donnée" of this screen.

Ambiguity

In the standard Ethernet II defined by the consortium TEN (that is to say Digital Equipment Corporation, Intel and Xerox), the EtherType field indicates the type of the protocol encapsulated in the field " données" Ethernet screen. It makes two bytes.

In the standardization of Ethernet led by the IEEE and leading to the standard 802.3, the EtherType field always makes two bytes but has a different direction according to its numerical value:

From 0 to 1500 (decimal value), it is interpreted like the field " longueur" and the length of the field " indicates; donnée".
Beyond 1536 (or 0600 into hexadecimal), it is interpreted like the Type field and indicates the nature of the protocol of higher level.

This double direction was defined in order to preserve same compatibility between 802.3 and TCP/IP which enters Ethernet and TCP/IP. Several RFC of IETF indeed refers explicitly to a field " type" in the protocol of the connection layer.

When weaves it is not an Ethernet screen, this field is conveyed by the heading SNAP/LLC (802.2). It is in particular the case for the protocols which do not depend on the IEEE but use underlayer LLC all the same (for example Fiber Distributed Data Interface).

The list of EtherTypes authorized as well as the recording of new types are spring of IEEE RAC EtherType Field Approval Authority.

EtherType for some current protocols

External bonds

IEEE, Authority of recording of EtherTypes EtherType Registration Authority
IEEE, List of EtherTypes

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