Subject: I need help with SLIP
To: None <>
From: Dejan Vucinic <>
List: current-users
Date: 11/07/1993 14:14:03

As my SLIP saga aproaches its third month, I concluded that it's time
to go get some help. :) So, here's most of it:

System: 486/33, VLB i/o card with FDC, HDC, parallel and serial junk
on it, USR Sportster 14400. (8Mb, Cheetah SVGA with Cirrus 5426, etc.)

Server: Cisco, MTU 1006 bytes, with or without header compression.

Problem: the SLIP session hangs. VERY thoroughly.

Description: I connect through tip, enter SLIP mode, exit OR suspend tip,
slattach, ifconfig, et voila. Everything works fine until I start a
transfer (also happens when lot of text scrolls in telnet). Then it just
stops at random. Lights on modem blink once more after about 10-15 seconds,
and then nothing. If I kill the slattach during these 15 secs and restart
it, it works as if nothing happened (ftp times out, but telnet doesn't
complain). If I don't kill slattach, I can't kill it at all after that
no matter what signals I send it, or whether or not I ifconfig it down.
On the other hand, if tip was only suspended, then I can kill slattach,
but cannot kill tip---looks like the last process that keeps /dev/com0
open can't die. When I have a zombie left (slattach or tip) at shutdown,
it won't shut the system down for about 10 minutes, obviously trying
to kill the zombie. All this doesn't depend on speed (tried from 2400
to 57600), flow control, or header compression. 

I am using current kernel from mid-october with fastintr com (?)patch.
Zmodem works fine, I can transfer megabytes without a single error with
X and compilation going on in other window. (BTW new com promptly kills
the box at 57600 when transfering certain files, for example uncompressed
com patch itself. :) The com patch only increased working time, all other
symptoms are the same. I also applied the CRAPPY_16450 patch, but this
one didn't change anything.

Since I know that lots of people are using the same software without any
problems, I assume that most of the trouble is in the weird hardware. 
However, I don't think that any PC hardware on the market can be considered
so weird that it should make the OS go berserk. I know of one soul who
had the same sort of trouble, but the guy had switched to FreeBSD and
claims to have no such problems anymore. So: I CAN spend a limited amount
of time working on this one, but I have no idea how to use the kernel
debugger or where to look for the problem without one, and this is where
I need help. Anyone interested in chasing this one with me?


P.S. tip just dumped core on me when I uploaded the file with ~>. Fortunately
     I learned the hard way that disabling DTR hangup on modem is *the right
     thing* to do. :)