From owner-freebsd-net  Wed Apr 18  8: 5:34 2001
Delivered-To: freebsd-net@freebsd.org
Received: from mighty.grot.org (mighty.grot.org [216.15.97.5])
	by hub.freebsd.org (Postfix) with ESMTP id 8363F37B422
	for <freebsd-net@freebsd.org>; Wed, 18 Apr 2001 08:05:32 -0700 (PDT)
	(envelope-from lists@grot.org)
Received: by mighty.grot.org (Postfix, from userid 998)
	id DA1855D10; Wed, 18 Apr 2001 08:05:31 -0700 (PDT)
Date: Wed, 18 Apr 2001 08:05:31 -0700
From: Adi <lists@lists.grot.org>
To: freebsd-net@freebsd.org
Subject: ICMP echo measurement discrepancy
Message-ID: <20010418080531.A35252@mighty.grot.org>
Reply-To: lists@lists.grot.org
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.2.5i
Sender: owner-freebsd-net@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.org

I have a SDSL 768K lightly loaded DSL circuit terminating on a Flowpoint 2200
SDSL router connected to an ethernet switch off of which I have 3 FreeBSD
machines:

<redback sms1000>---768K SDSL---<router>==[switch]===(FreeBSD machine)

I also control the ISP end of the DSL circuit. Depending on the *line
encapsulation of the SDSL circuit*, different programs running ICMP echo
report different packet loss rates with otherwise the _exact_ same setup.

If I run ping interactively on the command line, as in 

> ping -c 10 -n x

where x is the ISP router interface or any other "remote" IP address from one
of my FreeBSD machines, I see no packet loss, and it's been that way since the
day the circuit was installed.

To keep a historical measurement, I have a perl script that does the ping
every 5 minutes and keeps it in an RRD much like mrtg. In the perl script I've
used both a system call to fping or used Net::Ping. I currently prefer the
latter, but the effects are the same.

If the SDSL line encapsulation is set to PPP over ATM then I typically see no
packet loss at all to a variety of sites and have measurements over 4-5 months
to prove it.

However, if I use fping or Net::Ping from a script, it reports packet loss
quite "often" -- in fact fping seems to always report packet loss (I count the
number of returned packets in it's case).

The changes to the network are made over 1 hop away from any FreeBSD machines
and the traffic levels have remained the same and ping interactively reports
different results from 2 different programs run in the background...I'm
befuddled. Any ideas (I could run ping in the background I suppose)?

Thanks,
Adi

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-net" in the body of the message