From owner-freebsd-hackers Wed Jan 10 07:37:46 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id HAA11114 for hackers-outgoing; Wed, 10 Jan 1996 07:37:46 -0800 (PST) Received: from etinc.com (et-gw.etinc.com [165.254.13.209]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id HAA11106 for ; Wed, 10 Jan 1996 07:37:41 -0800 (PST) Received: from dialup7.etinc.com (dialup7.etinc.com [204.141.95.142]) by etinc.com (8.6.11/8.6.9) with SMTP id KAA24188 for ; Wed, 10 Jan 1996 10:49:02 -0500 Date: Wed, 10 Jan 1996 10:49:02 -0500 Message-Id: <199601101549.KAA24188@etinc.com> X-Sender: dennis@etinc.com X-Mailer: Windows Eudora Version 2.0.3 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: hackers@freebsd.org From: dennis@etinc.com (dennis) Subject: Re: Using `ping' to diagnose network connections reasonable? Sender: owner-hackers@freebsd.org Precedence: bulk >Jordan K. Hubbard writes: >> >> I'd like to add some code to sysinstall which will attempt to >> `diagnose' a link before accepting the configuration parameters, >> catching a lot of adapter misconfiguration and incorrect data errors >> that sysinstall misses now (to fail less gracefully later). My >> question is whether or not `ping' is a reasonable way to measure >> connectivity between your host and the gateway & dns machines. Is it >> reasonable to assume that if a host supports forwarding or DNS >> queries, it will also answer pings? What if you've got pings blocked >> somehow but allow DNS traffic through? I wouldn't want to flag a host >> as `unreachable' when in fact it would have worked fine for its >> intended purpose! That would be worse than no error checking at all. > >Well, here are three possibilities to consider: > >1. I have an ISDN dialup connection, and I don't like people costing > me money by pinging me, so I have got my ISP to drop ICMP packets > at his end. > >2. I have an PPP dialup connection, and I haven't got my ISP to drop > ICMP packets at his end. Still, setting up the connection takes > so long that the first 20 packets fall into the bit bucket. > >3. I have a machine with an independent IP processor. If the main > machine fails, you can't talk to it (how about that), but you can > still ping it. This isn't made up, I really do have a machine > like that (based on a 68020, would you believe, but the IP > processor is an 80386 :-). > >In each of these cases, your ping check may come to an incorrect >conclusion. Pinging is nice for an approximation, but it's no >substitute for the real thing. Surely this is the "exception" and not the rule! Imagine if everyone was set up like this?????? db ---------------------------------------------------------------------------- Emerging Technologies, Inc. http://www.etinc.com Synchronous Communications Cards and Routers For Discriminating Tastes. 56k to T1 and beyond. Frame Relay, PPP, HDLC, and X.25