From owner-freebsd-current  Thu Dec 23  0: 7:23 1999
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Date: Thu, 23 Dec 1999 00:07:10 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
Message-Id: <199912230807.AAA00697@apollo.backplane.com>
To: Bill Paul <wpaul@skynet.ctr.columbia.edu>, julian@whistle.com,
	scottm@CS.UCLA.EDU, jlemon@americantv.com, brad@shub-internet.org,
	jabley@patho.gen.nz, phk@critter.freebsd.dk,
	wollman@khavrinen.lcs.mit.edu, current@freebsd.org
Subject: Re: Woa!  May have found something - 'rl' driver and small packets (was Re: Odd TCP glitches in new currents)
References: <199912230641.BAA10453@skynet.ctr.columbia.edu> 
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    Ok, here's the current status:  The RealTek boards ('rl' driver, D-Link
    brand, RealTek chip vendor) appear to have serious packet loss problems 
    with small packets.  The cause is currently unknown.  I had two different 
    machines (an older PPro 200 and a somewhat newer K6-2/233) with the 
    boards in and both exhibited the problem.

    The problem is fairly trivial to reproduce using linktest:

	http://www.backplane.com/FreeSrc/linktest-1.1.c

	host1# linktest -s 16 -f8 host2
	host1# linktest -s 16 -f8 host1

    These boards were the cause of my TCP problems.

    The D-Link boards came with the D-Link switch I had purchased.  I removed
    the boards and replaced them with the two LinkSys boards that came with
    the LinkSys switch I had purchased.

    The LinkSys boards ('dc' driver, LNE100TX+ fame, LC82C115 PNIC II vendor)
    do not appear to have the packet loss problem.  I have not had a 
    reoccurance of my TCP glitches and my linktest tests have all come out
    roses.

    I'm hoping Bill will be able to find the problem with the D-Link boards,
    just so everyone else using them doesn't hit the same hangup, but my
    problem at least appears to be solved after replacing the boards.  I've
    stuck my D-Link board into another diskless test machine and it's 
    available for testing potential fixes, debugging, etc.

    In regards to the switches themselves:  Both the LinkSys and the D-Link
    5-Port switches appear to work well.  I've interchanged them with each
    other and tested them pretty significantly with four machines attached.
    The LinkSys seems to be limited to around 25 MBytes/sec in aggregate
    throughput.  The D-Link maxed out my machines (35 MBytes/sec) so I do
    not know what it's ultimate limitation is.  The small-packet test maxed
    out my machines at 35,000 packets per second.  So while I couldn't find
    the limitations of the switches, they're plenty good enough for me!

    The only problem I've come up against is that when I change the duplex
    with ifconfig the ethernet port is not reset and the switches do not
    recognize that the duplex has changed.  If I 'ifconfig XXX media auto',
    however, the ports are reset and the switches negotiate full-duplex
    properly.  If I ifconfig between 10 and 100BaseT the ports are reset and
    the switches appear to figure out the mode properly as well.

    So that's where I am.  There was never anything wrong with the switches
    or the cabling - the entire problem was due to the D-Link ethernet cards.

						-Matt



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