Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!rutgers!sri-unix!sri-spam!mordor!lll-lcc!pyramid!voder!blia!ted
From: ted@blia.UUCP
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet Compatibility...
Message-ID: <1622@blia.BLI.COM>
Date: Mon, 9-Feb-87 16:01:04 EST
Article-I.D.: blia.1622
Posted: Mon Feb  9 16:01:04 1987
Date-Received: Tue, 10-Feb-87 07:06:45 EST
References: <4312@columbia.UUCP> <144000002@tiger.UUCP>
Organization: Britton Lee, Los Gatos, CA
Lines: 30
Summary: The fields overlap

In article <144000002@tiger.UUCP>, rvk@tiger.UUCP writes:
>                      ....  I had an Entre salesman (take this with a
> grain of salt) tell that some ethernet boards incorrectly interpret
> an IEEE 802.3 "length" field as a "type" field.  I have not been able to
> determine the accuracy of the latter statement.

You can thank the IEE 802 committee for this one (or perhaps the Xerox-Intel-
DEC tramatic trio)! The IEEE 802.3 length field is in the same place as the
Ethernet protocol type field.

DEC's newer generation of Ethernet interfaces handle both protocols by looking
at the 802.3 length field and if that is larger than a legal packet size (1548
or whatever that magic number is), it assumes that the packet is in the
Ethernet format. It looks like most of the protocol types assigned by Xerox
are large enough to make that work. But if anyone decides to use a small
value there, a lot of sites will be in trouble.

===============================================================================
            Ted Marshall
            Britton Lee, Inc.
p-mail:     14600 Winchester Blvd, Los Gatos, Ca 95030
voice:      (408)378-7000
uucp:       ...!ucbvax!mtxinu!blia!ted
ARPA:       mtxinu!blia!ted@Berkeley.EDU
disclaimer: These opinions are my own and may not reflect those of my employer;
            I leave them alone and they leave me alone.
fortune for today:
Worst Month of 1981 for Downhill Skiing:
	August.  The lines are the shortest, though.
		-- Steve Rubenstein