tcp-ip@ucbvax.ARPA (05/16/85)
From: Ira Winston <Ira%upenn.csnet@csnet-relay.arpa> I am involved in planning a campus-wide IEEE 802.3/802.2 based network. Does anyone have any ideas as to how IP datagrams will appear on this type of network? From what I understand there are two possibilities: 1) Avoid 802.2 and use the 802.3 length field as a type field 2) Strictly adhere to 802.2/802.3 standards using the length field as a length field and use the 802.2 SSAP/DSAP for the type field. Which of these methods is going to become the standard?
tcp-ip@ucbvax.ARPA (05/17/85)
From: "J. Noel Chiappa" <JNC@MIT-XX.ARPA> I think that there was some compromise worked out where if the value in the type/length field is larger than the largest legal Ethernet packet (1500) then it was to be interpreted as a type field. This lets out most of the common values for that field, including IP and ARP. This basically legalized the de facto standard, which was that everyone was ignoring the SAP stuff. (The exact use of having an optional length field if you have to be able to function without it was never made clear. But remember, being a standards committee means never having to say 'Yow, are we gratuitously kludgy yet?') Noel -------
tcp-ip@ucbvax.ARPA (05/17/85)
From: Kluger.osbunorth@Xerox.ARPA A second to Noel's message... There is a footnote in the adopted version of the IEEE 802.3 specification that says "Packets with a length field value greater than those specified in 4.4.2 [1518 decimal] may be ignored, discarded, or used in a private manner. The use of such packets is beyond the scope of this standard." The "private manner" referred to is (of course) use as a type field. Larry