SUMMARY (sort of): How to determine if a SLIP line is active

From: Amir J. Katz (
Date: Thu Aug 19 1993 - 21:42:59 CDT

Following a previous inquiry whether a SLIP device can be monitored, I
posted another query:

>> I have a SLIP (version 4.0) connection on a dial-up line. I would like to
>> use cron to dial at, say 2 AM, leave the line open for 10 minutes, then shut
>> it down. So far, a piece of cake. However, before I'm shutting down the link
>> I want to make sure that it's not in a middle of a heavy FTP or a long mail
>> transfer. How can I do this?
>> Previous suggestions were:
>> 1. Use tcpdump - the downside is that 'bpf' needs to be installed and on
>> Sun boxes this is possible only if you have kernel sources (with the
>> license, of course).
>> 2. Install cslip-2.1 which contains 'slstats' which shows statistics on the
>> SLIP line action. The downside - I need to install cslip instead of slip
>> (most say it's an improvement, since cslip is faster).
>> Any other suggestions? Thanks in advance.

- Most people suggested doing successive netstats and record the number of
  packets still moving until it drops below a threshold you can live with.

- John Lengeling <> said to use tcpdump, but to make sure
  that rpc.etherd is started first.

- (J. Matt Landrum) said:
     I don't know about SLIP, but programs like Morningstar's PPP have
     filters that will determine if the line is active and keep the
     connection up (or allow it to go down) depending on the type of
     packet... user configurable.

My Comments:
1. netstat -i is not reliable -
   a) Sometimes it takes forever for it to show the SLIP stats
   b) Even when I had heavy ftp and mails, the numbers were inconclusive.

2. I tried tcpdump with rcp.etherd running on both le0 and slip0, but it
   showed nothing. It said:

     tcpdump: listening on slip0

   and it just sat there.

3. I'm not sure I want to put any effort in installing a better SLIP
   package, since we're going to upgrade to PPP anyway.

Thanks to: (Kevin Sheehan {Consulting Poster Child}) (Glenn Satchell - Uniq Professional Services) (J. Matt Landrum) (Todd Pfaff)
 Patrick O'Callaghan <>
 Dan Stromberg - OAC-DCS <>
 kmah@DCS-Systems.COM (Kevin Mah)
 John Lengeling <>

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/*  Amir J. Katz         | amir@matis.ingr.COM,     */
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