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From: rk@lexicon.com (Bob Kukura)
Newsgroups: comp.protocols.tcp-ip,comp.dcom.lans
Subject: Re: Another NCSA telnet question (I rtfm already)
Message-ID: <444@lexicon.com>
Date: 1 Jun 89 16:58:28 GMT
References: <1869@leah.Albany.Edu>
Organization: Lexicon, Inc., Waltham, MA
Lines: 36
In-reply-to: rds95@leah.Albany.Edu's message of 31 May 89 17:36:41 GMT

In article <1869@leah.Albany.Edu> rds95@leah.Albany.Edu (Robert Seals) writes:

> Well, ncsa telnet is sure neato, but I am having one real big
> problem. I am unable to transfer certain files from the remote machine
> to my PC. I can send from the PC to the remote machine, and it seems
> that small files will go back, but usually, it says "150 Opening
> connection\n" and then sits there doing nothing. File transfer is
> enabled, and the standalone ftp did the same kind of
> thing. My machine is a 386 with the WD8003; the remote machine is
> a uVaxII with Ultrix 1.2.
> 
> (I just tested the same thing connected to a Unisys 7000 (CCI 6/32) with
> 4.3-tahoe, and it worked. Darn. Well, does this mean that Ultrix is the
> stinker?)
> 
> rob

 We had a problem with very similar symptoms using PC-NFS with Ultrix.
Very small telnet and ftp transfers worked fine, but larger ones
failed.

 Ultrix uses trailer encapsulation, which moves the variable-sized
packet header data to the end of the packet so that the received
packet data is page-aligned can be mapped into the user address space
without having to copy it.  PC-NFS could not handle trailer
encapsulated packets, which Ultrix apparently only generated when
doing transfers larger that about 1.5 K.

 The solution was to edit the -trailers option into the /etc/ifconfig
line in the rc.local file on each Ultrix system to disable trailer
encapsulation.  This is no longer necessary as of Ultrix V3.0, which
negotiates with each host on whether to use trailer encapsulation.
-- 
-Bob Kukura		smart: rk@lexicon.com
			dumb: {husc6,linus,harvard,bbn}!spdcc!lexicon!rk
			phone: (617) 891-6790