Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!hc!hi!cyrus
From: cyrus@hi.unm.edu (Tait Cyrus)
Newsgroups: comp.protocols.tcp-ip
Subject: packet lengths
Message-ID: <23572@hi.unm.edu>
Date: 15 Apr 88 17:15:33 GMT
Organization: U. of New Mexico, Albuquerque
Lines: 28
Keywords: packet lengths vs IP lengths



I have been comparing the lengths of packets specified in IP headers
against actual packet lengths.  What I am seeing, ignoring IP packets
smaller than the minimum packet size, is that a fair number of machines
send out packets that are 1-3 bytes longer than is specified by the
IP length.  Although this does not hurt anything, I am wondering
why this is.  Is it because some machines short/long/quad align the
end of the packet before sending?

Also, this phenomenon appears to be protocol dependent.  For example,
I saw several 4.3 machines doing this when sending out timed packets
and routed packet, but not with other packets.  I've seen our IP/TCP
Imagen sending out UDP packets doing this.

Although this does not hurt anything, I am just curious as to the reason
why.


-- 
    @__________@    W. Tait Cyrus   (505) 277-0806
   /|         /|    University of New Mexico
  / |        / |    Dept of Electrical & Computer Engineering 
 @__|_______@  |       Parallel Processing Research Group (PPRG)
 |  |       |  |       UNM/LANL Hypercube Project
 |  |  hc   |  |    Albuquerque, New Mexico 87131
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 @/_________@/        cyrus@hc.dspo.gov