Case 8000 Series Reference Manual page 132

DIX defines that frames contain a 2-byte type field as opposed to a 2-byte
length field in the ISO/IEEE specifications. The addressing parts of the
frame are identical in both the IEEE and DIX specifications.
The type field has the advantage of using the same cabling for efficiently
operating many different protocol sets (e.g. DECNet, DEC.LAT, TCP/IP,
etc) without fear of interference. The IEEE specifications however do not
allow such flexibility.
In some vendor networks it is possible to intermingle the ISO framing with
DIX framing, since most DIX frame types are equivalent to an illegal ISO
length field (TCP/IP is an example), and most IEEE systems do not
generate frames big enough for the length field to be a valid type field.
Therefore the two protocol sets can often coexist on the same cabling.
Furthermore, most vendors' IEEE LAN bridges will transport complete
Ethernet frames without regard to the length or type field contained
within them. As a result, most bridges (Cray bridges included) can be used
with TCP/IP and IEEE 802.2 protocols.
Router is designed to use IEEE 802.3 Transceivers and supports the
Ethernet framing method for use on standard TCP/IP LANs.
X870-300351 Issue 1 C-8 Rev.0