Date   : Sun, 21 Nov 2010 00:03:52 +0000
From   : pete@... (Pete Turnbull)
Subject: Rockin' out with awServer :-)

Rick Murray wrote:
> On 20/11/2010 13:05, Pete Turnbull wrote:

>> The choice seems to have been made then to assume that any
>> number in that field bigger than 1518 (now 1522, allowing for 802.1p/q
>> QoS and VLAN tags) was a type indicator, and anything small was a length
>> indicator.
> 
> ;-) You probably shouldn't make odd assumptions

Nobody made any assumptions in the way you're worried about.  I 
expressed that poorly.  The original Ethernet spec was agreed between 
DEC, Intel and Xerox, who were represented on the 802.3 committee that 
defined the later standard.  Xerox were able to show that sizes up to 
1500, or a little higher, were safe (no useful types had been allocated 
lower numbers), so it was adopted as a formal part of the standard.  In 
that field, any value under 0x600 is a size, anything else is a type. 
What I meant was that as result of that standardisation, anyone or any 
software examining that field can assume that it's a size or a type, 
accordingly.  Perhaps I should have used the verb "decide" instead of 
"assume".

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York