Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!spool.mu.edu!uunet!aria!dumbcat!marc
From: marc@dumbcat.sf.ca.us (Marco S Hyman)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Packet Sizes
Message-ID: <271@dumbcat.sf.ca.us>
Date: 24 Mar 91 02:33:08 GMT
References: <7741@uceng.UC.EDU> <9103151236.AA05472@asylum.sf.ca.us>
	<17724@sdcc6.ucsd.edu>
Organization: MH Software, Hayward, CA.
Lines: 29

In article <17724@sdcc6.ucsd.edu> jclark@sdcc6.ucsd.edu (John Clark) writes:
    In article <9103151236.AA05472@asylum.sf.ca.us> romkey@asylum.sf.ca.us writes:
    +If you're looking at raw ethernet packet lengths (as opposed to IP
    +datagram lengths), you'll see lots of 60 byte packets on the net
    +because ethernet has a minimum packet length of 60 bytes. Any packets
    +that are shorter are padded out to 60. IP can tell how many bytes it
    
    Sometime ago I had a ethernet analyzer on a line with both TCP/IP
    and DECNET traffic. It seems to me that there were some DECNET
    packets shorter than the minimum. It could have been a halucination
    or does DEC violate the standard.

Unlikely.  And it depends upon what you're measuring.  A standard (D-I-X)
ethernet frame consists of:

	6 octets of destination
	6 octets of source
	2 octets of type
	46-1500 octets of data
	4 octets of CRC

The minimum frame size is 64 octets (plus 64 bits of preamble and 9.6 us of
interframe spacing). It is possible you were using a "smart" analyzer that
knows the protocol formats well enough to not display fill characters used to
force the frame to the proper minimum size.
-- 
// marc
// home: marc@dumbcat.sf.ca.us		{decwrl,sun}!pacbell!dumbcat!marc
// work: marc@ascend.com		uunet!aria!marc