Ping

Gisteren, na een gesprekje met mijn broer, opgezocht wat het aloude ping-commando eigenlijk precies doet, technisch. Via de wikipedia-pagina, die een goede introductie geeft, werd ik doorgesluisd naar de ontstaansgeschiedenis van de unix-hack, geschreven door de maker ervan, Mike Muuss (1958-2000).

Op zijn (nog steeds operationele) homepage staat een grappige anecdote over een netwerkbeheerder die de sonar-etymologie wel heel letterlijk nam, en als een yellow submarine op ethernetkabels loos ging:

The best ping story I’ve ever heard was told to me at a USENIX conference, where a network administrator with an intermittent Ethernet had linked the ping program to his vocoder program, in essence writing:

ping goodhost | sed -e 's/.*/ping/' | vocoder

He wired the vocoder’s output into his office stereo and turned up the volume as loud as he could stand. The computer sat there shouting “Ping, ping, ping…” once a second, and he wandered through the building wiggling Ethernet connectors until the sound stopped. And that’s how he found the intermittent failure.

Maar ook de alligorice bespreking van The Story About Ping door Marjorie Flack en Kurt Wiese, een oud kinderboek over de wedervaren van een eendje op de Yantze-rivier, door een lezer uit “Upper Volta, Uzbekistan”, op “March 7, 1999 “, die Muuss op zijn homepage verhaalt, mag er best zijn:

Excellent, heart-warming tale of exploration and discovery. Using deft allegory, the authors have provided an insightful and intuitive explanation of one of Unix’s most venerable networking utilities. Even more stunning is that they were clearly working with a very early beta of the program, as their book first appeared in 1933, years (decades!) before the operating system and network infrastructure were finalized.

The book describes networking in terms even a child could understand, choosing to anthropomorphize the underlying packet structure. The ping packet is described as a duck, who, with other packets (more ducks), spends a certain period of time on the host machine (the wise-eyed boat). At the same time each day (I suspect this is scheduled under cron), the little packets (ducks) exit the host (boat) by way of a bridge (a bridge). From the bridge, the packets travel onto the internet (here embodied by the Yangtze River).

The title character — er, packet, is called Ping. Ping meanders around the river before being received by another host (another boat). He spends a brief time on the other boat, but eventually returns to his original host machine (the wise-eyed boat) somewhat the worse for wear.

The book avoids many of the cliches one might expect. For example, with a story set on a river, the authors might have sunk to using that tired old plot device: the flood ping. The authors deftly avoid this.

Who Should Buy This Book

If you need a good, high-level overview of the ping utility, this is the book. I can’t recommend it for most managers, as the technical aspects may be too overwhelming and the basic concepts too daunting.

Problems With This Book

As good as it is, The Story About Ping is not without its faults. There is no index, and though the ping(8) man pages cover the command line options well enough, some review of them seems to be in order. Likewise, in a book solely about Ping, I would have expected a more detailed overview of the ICMP packet structure.

But even with these problems, The Story About Ping has earned a place on my bookshelf, right between Stevens’ Advanced Programming in the Unix Environment, and my dog-eared copy of Dante’s seminal work on MS Windows, Inferno. Who can read that passage on the Windows API (“Obscure, profound it was, and nebulous, So that by fixing on its depths my sight — Nothing whatever I discerned therein.”), without shaking their head with deep understanding. But I digress.

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