diff --git a/_data/navigation.csv b/_data/navigation.csv index 4c034b1..d0c6729 100644 --- a/_data/navigation.csv +++ b/_data/navigation.csv @@ -8,6 +8,7 @@ link dump,/linklink timezone,/oneshot/timezone coding bibble,/oneshot/codingbible footgun,/oneshot/footgun +500 miles,/oneshot/500miles guestbook,http://users3.smartgb.com/g/g.php?a=s&i=g36-36498-b6 direct message me,/personal/qa thanks page,/thanks diff --git a/oneshot/500miles.md b/oneshot/500miles.md new file mode 100644 index 0000000..73d52e5 --- /dev/null +++ b/oneshot/500miles.md @@ -0,0 +1,147 @@ +--- +title: 500 miles +--- +## Sourced from <https://web.mit.edu/jemorris/humor/500-miles> + +From: Trey Harris <trey@sage.org> + +Here's a problem that *sounded* impossible... I almost regret posting +the story to a wide audience, because it makes a great tale over drinks +at a conference. :-) The story is slightly altered in order to protect +the guilty, elide over irrelevant and boring details, and generally make +the whole thing more entertaining. + +I was working in a job running the campus email system some years ago +when I got a call from the chairman of the statistics department. + +"We're having a problem sending email out of the department." + +"What's the problem?" I asked. + +"We can't send mail more than 500 miles," the chairman explained. + +I choked on my latte. "Come again?" + +"We can't send mail farther than 500 miles from here," he repeated. "A +little bit more, actually. Call it 520 miles. But no farther." + +"Um... Email really doesn't work that way, generally," I said, trying +to keep panic out of my voice. One doesn't display panic when speaking +to a department chairman, even of a relatively impoverished department +like statistics. "What makes you think you can't send mail more than +500 miles?" + +"It's not what I *think*," the chairman replied testily. "You see, when +we first noticed this happening, a few days ago--" + +"You waited a few DAYS?" I interrupted, a tremor tinging my voice. "And +you couldn't send email this whole time?" + +"We could send email. Just not more than--" + +"--500 miles, yes," I finished for him, "I got that. But why didn't +you call earlier?" + +"Well, we hadn't collected enough data to be sure of what was going on +until just now." Right. This is the chairman of *statistics*. "Anyway, +I asked one of the geostatisticians to look into it--" + +"Geostatisticians..." + +"--yes, and she's produced a map showing the radius within which we can +send email to be slightly more than 500 miles. There are a number of +destinations within that radius that we can't reach, either, or reach +sporadically, but we can never email farther than this radius." + +"I see," I said, and put my head in my hands. "When did this start? +A few days ago, you said, but did anything change in your systems at +that time?" + +"Well, the consultant came in and patched our server and rebooted it. +But I called him, and he said he didn't touch the mail system." + +"Okay, let me take a look, and I'll call you back," I said, scarcely +believing that I was playing along. It wasn't April Fool's Day. I +tried to remember if someone owed me a practical joke. + +I logged into their department's server, and sent a few test mails. +This was in the Research Triangle of North Carolina, and a test mail to +my own account was delivered without a hitch. Ditto for one sent to +Richmond, and Atlanta, and Washington. Another to Princeton (400 miles) +worked. + +But then I tried to send an email to Memphis (600 miles). It failed. +Boston, failed. Detroit, failed. I got out my address book and started +trying to narrow this down. New York (420 miles) worked, but Providence +(580 miles) failed. + +I was beginning to wonder if I had lost my sanity. I tried emailing a +friend who lived in North Carolina, but whose ISP was in Seattle. +Thankfully, it failed. If the problem had had to do with the geography +of the human recipient and not his mail server, I think I would have +broken down in tears. + +Having established that -- unbelievably -- the problem as reported was +true, and repeatable, I took a look at the sendmail.cf file. It looked +fairly normal. In fact, it looked familiar. + +I diffed it against the sendmail.cf in my home directory. It hadn't been +altered -- it was a sendmail.cf I had written. And I was fairly certain +I hadn't enabled the "FAIL_MAIL_OVER_500_MILES" option. At a loss, I +telnetted into the SMTP port. The server happily responded with a SunOS +sendmail banner. + +Wait a minute... a SunOS sendmail banner? At the time, Sun was still +shipping Sendmail 5 with its operating system, even though Sendmail 8 was +fairly mature. Being a good system administrator, I had standardized on +Sendmail 8. And also being a good system administrator, I had written a +sendmail.cf that used the nice long self-documenting option and variable +names available in Sendmail 8 rather than the cryptic punctuation-mark +codes that had been used in Sendmail 5. + +The pieces fell into place, all at once, and I again choked on the dregs +of my now-cold latte. When the consultant had "patched the server," he +had apparently upgraded the version of SunOS, and in so doing +*downgraded* Sendmail. The upgrade helpfully left the sendmail.cf +alone, even though it was now the wrong version. + +It so happens that Sendmail 5 -- at least, the version that Sun shipped, +which had some tweaks -- could deal with the Sendmail 8 sendmail.cf, as +most of the rules had at that point remained unaltered. But the new +long configuration options -- those it saw as junk, and skipped. And +the sendmail binary had no defaults compiled in for most of these, so, +finding no suitable settings in the sendmail.cf file, they were set to +zero. + +One of the settings that was set to zero was the timeout to connect to +the remote SMTP server. Some experimentation established that on this +particular machine with its typical load, a zero timeout would abort a +connect call in slightly over three milliseconds. + +An odd feature of our campus network at the time was that it was 100% +switched. An outgoing packet wouldn't incur a router delay until hitting +the POP and reaching a router on the far side. So time to connect to a +lightly-loaded remote host on a nearby network would actually largely be +governed by the speed of light distance to the destination rather than by +incidental router delays. + +Feeling slightly giddy, I typed into my shell: + +$ units +1311 units, 63 prefixes + +You have: 3 millilightseconds +You want: miles + * 558.84719 + / 0.0017893979 + +"500 miles, or a little bit more." + +Trey Harris +-- +I'm looking for work. If you need a SAGE Level IV with 10 years Perl, +tool development, training, and architecture experience, please email +me at trey@sage.org. I'm willing to relocate for the right opportunity. + + +