Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!hellgate.utah.edu!cs.utah.edu!haas
From: haas@cs.utah.edu (Walt Haas)
Newsgroups: comp.dcom.lans
Subject: Re: Multiple Novell Servers on on eEthernet
Message-ID: <1990Feb23.185608.8785@hellgate.utah.edu>
Date: 24 Feb 90 01:56:07 GMT
References: <539@opus.NMSU.EDU> <1990Feb20.113920.19222@hellgate.utah.edu> <7270.25e3b569@dit.ie>
Organization: University of Utah CS Dept
Lines: 45

In article <7270.25e3b569@dit.ie> alawlor@dit.ie (Aengus Lawlor) writes:
>In article <1990Feb20.113920.19222@hellgate.utah.edu>, I wrote
>> ... Also I would recommend that you plan for the future and
>> insist that all Novell machines use ECONFIG to generate Ethernet packet
>> framing, so that you don't run into problems with 802.2 DSAP=FF SSAP=FF
>> at some future time.
>> 
>> Cheers  -- Walt Haas    haas@cs.utah.edu
>Two questions.
>  1) Can somebody explain to me what ECONFIG is for?

When a Novell device puts a packet onto an Ethernet, it puts a header
around it.  There are two standards for such headers:

1) The original Ethernet or DIX (DEC/Intel/Xerox) standard, which
   consists of:
	48 bit destination address
	48 bit source address
	16 bit protocol type
	...    user data

2) The IEEE 802.3 standard, which consists of:
	48 bit destination address
	48 bit source address
	16 bit length

The two packet formats can be intermixed on one wire, because all Ethernet
protocol types have numbers greater than the maximum legal 802.3 length,
thus a received packet can be examined and assigned confidently to one
class or the other.

HOWEVER the proper thing to follow the length field in format 2) is an
IEEE 802.2 header.  Instead, Novell inserts an XNS checksum of all one's
(I think I got that right).  This would appear to the world as an IEEE 802.2
DSAP=FF and SSAP=FF.

Router vendors who support Novell protocols, such as cisco, deal with
the DSAP=FF SSAP=FF packet as a special case.  I fear that this hack will
break in the next year or two as the use of the 802.3 framing style becomes
more widespread.  The easiest precaution, and the one that we take here,
is to use the ECONFIG option which causes the Novell device to generate
header format 1).  This makes the packet fully conformant to standard so
there should be no problem.

Cheers  -- Walt