Date: Wed, 10 Jan 1996 10:49:02 -0500 From: dennis@etinc.com (dennis) To: hackers@freebsd.org Subject: Re: Using `ping' to diagnose network connections reasonable? Message-ID: <199601101549.KAA24188@etinc.com>
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>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
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