Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utcs!mnetor!seismo!caip!nike!ucbcad!ucbvax!SRI-SPAM.ARPA!gds
From: gds@SRI-SPAM.ARPA.UUCP
Newsgroups: mod.protocols.tcp-ip
Subject: Re: Am I imagining things?
Message-ID: <8607120947.AA11480@sri-spam.arpa>
Date: Sat, 12-Jul-86 05:47:44 EDT
Article-I.D.: sri-spam.8607120947.AA11480
Posted: Sat Jul 12 05:47:44 1986
Date-Received: Sat, 12-Jul-86 10:29:57 EDT
References: <8606302206.AA07389@nrl-aic>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 39
Approved: tcp-ip@sri-nic.arpa

In article <8606302206.AA07389@nrl-aic>, hemphill@NRL-AIC.ARPA (Gavin Hemphill) writes:
> 
> 	Sorry about the previous empty message -- fumble fingers strikes again.
> 
> 	Is it my imagination or are other people experiencing problems as
> well.  I have noticed lately that I can't FTP files bigger than 20 or 30 KB.
> The symptoms are that after 6 or 7 minutes (clock time) the FTP connections
> (to wherever from nrl-aic) break, there are no messages or indications from
> the remote server just the "ftp>" prompt.  Secondary to this when I try to
> open a new connection to the same host I'll get the "host unreachable" 
> message, but if I telnet to any other host -- and from there FTP or telnet 
> to my original destination I can get through, and after backing out of that 
> a direct FTP will again get through.  Anybody else had similar problems?  If 
> so, any pointers would be appreciated.
> 	G++

Sounds like a couple of problems.  The "host unreachable" message could be
caused, if you are talking to an imp, by the bug in the imp driver that
causes a destination host to be marked down because no packets can be deliv-
ered to it.  This can be fixed by changing the value of HOSTTIMER in
/sys/netimp/if_imp.h from 128 to a smaller number (I used 1 instead of 0
because our imp was crashing and I did not want to deliver packets too
quickly to it).

The ftp lockup problems sound like the "bad file number" problems we were
having a few months ago and a related problem with getting "connection
error" messages telnetting from a tiu on a prnet to a vax on the arpanet.
I discovered that the connection errors were coming when a gateway from
the arpanet to the prnet was having trouble fragmenting a packet of odd
byte length > 254.  By changing the arpanet mtu on the vax from 982 (act-
ually arpanet-pli mtu) to 254 the problem went away.  Likewise, many of
our bad file number and ftp lockup problems went away when I had the
ethernet mtu changed from 1500 to 576.

Next time this happens try and figure out to where you were trying to con-
nect, and what (if any) gateways you had to go through to get there.  If
possible, monitor the tcp connection looking for a reset (by doing netstats
this will show as a connection going from ESTABLISHED to not showing up at
all).  If you can turn on tcp debugging, look for a RST packet coming in.