Path: utzoo!mnetor!uunet!husc6!cmcl2!beta!hc!ames!elroy!mahendo!earle
From: earle@mahendo.JPL.NASA.GOV (Greg Earle)
Newsgroups: comp.windows.x
Subject: Re: expo ftp bug?
Message-ID: <5674@elroy.Jpl.Nasa.Gov>
Date: 9 Mar 88 11:24:52 GMT
References: <8803052358.aa24854@SMOKE.BRL.ARPA> <7786@tut.cis.ohio-state.edu>
Sender: news@elroy.Jpl.Nasa.Gov
Organization: Gainfully Unemployed Ltd., Lakeview Terrace  CA
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In-reply-to: bob@allosaur.cis.ohio-state.edu's message of 6 Mar 88 15:53:54 GMT


expo is probably running vanilla SunOS 3.4.  There are various TCP bugs in
vanilla 3.4; one is that sometimes an initiator will for some bizarre reason
present a 64K TCP window to the other end, and slowly but surely the window
will get eaten away until it is zero, and then your TCP/IP service (oft times
an FTP) will hang.  Another is that when negotiating the Maximum Segment Size
the packet size would get set to 512 bytes always.  I have this feeling that
one of these bugs is causing the famed 511999 bug (I was bitten as well).
There is another variant to it; even more insidious is getting all 512000 
bytes and discovering only after unsplitting that a file is corrupted.  In both
the 511999 and this case, the very first byte of the last 512-byte block of
the file gets dropped.  In the 511999 case, that is all there is to it.  In
the even-more-insidious case, the first byte is dropped and the last byte is
*replicated* (i.e., instead of [0-512] we get [1-511]511).  This happened to
me with core.src.tar.Z.split.ac.

In short: expo should be running either (at least) SunOS 3.4.2, or SunOS 3.5.
If you have a Sun at the receiving end, make sure it is at 3.4.2 or 3.5, and
both you and expo should install the tcp_mss patch.  This patches the
locations tcp_mss+0xac & tcp_mss+0xbc in /vmunix (and /dev/kmem) to be 1024,
not 512 (this is a workaround - `Fixed in 4.0' ... ):

yourmachine:1 # adb -w -k /vmunix /dev/mem		<==
sbr f06aa18 slr	649
physmem	1fe
tcp_mss+0xac?d						<==
_tcp_mss+0xac:	 512
tcp_mss+0xac?w 0x400					<==
_tcp_mss+0xac: 0x200	= 0x400
tcp_mss+0xac/d						<==
_tcp_mss+0xac:	 512
tcp_mss+0xac/w 0x400					<==
_tcp_mss+0xac: 0x200	= 0x400
tcp_mss+0xbc?d						<==
_tcp_mss+0xbc:	 512
tcp_mss+0xbc?w 0x400					<==
_tcp_mss+0xbc: 0x200	= 0x400
tcp_mss+0xbc/d						<==
_tcp_mss+0xbc:	 512
tcp_mss+0xbc?w 0x400					<==
_tcp_mss+0xbc: 0x200	= 0x400
tcp_mss+0xbc?d						<==
_tcp_mss+0xbc:  1024
^D							<==
yourmachine:2 #

[ Sorry to turn xpert into a Sun kernel & TCP discussion, but the keepers of
  `expo' might want to consider this, due to the FTP problems ...  - Greg ]

--
	Greg Earle		earle@mahendo.JPL.NASA.GOV
	Indep. Sun consultant	earle%mahendo@jpl-elroy.ARPA	[aka:]
	(Gainfully Unemployed)	earle%mahendo@elroy.JPL.NASA.GOV
	Lake View Terrace, CA	...!{cit-vax,ames}!elroy!jplgodo!mahendo!earle