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Rook
Asked: 2012-06-10 11:28:04 +0800 CST

The use of the underscore in host names

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Wikipedia states that underscores are used by both Android and Microsoft Windows Systems in hostnames. My question is, what are these host names used for? Do you know list of these strange hostnames? Have you ever even seen one of these?

windows domain-name-system android

3 Answers

  1. Per RFC952, hostnames are:

    A "name" (Net, Host, Gateway, or Domain name) is a text string up to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus sign (-), and period (.). Note that periods are only allowed when they serve to delimit components of "domain style names".

    Microsoft in the usual "Embrace, Extend and Extinguish™" method they use, have these for certain functions within their DNS system they use for domains and extended it to include allowing hostnames to resolve, probably because NETBIOS names allowed underscores and it was easier just to slap it lower case onto the front of the domain to come up with a machine hostname. It sometimes makes zone transfers a real pain as the entries are not RFC compliant.

    I would assume that Google, being the 900 lb Gorilla, has done the same thing for similar reasons. Which means that access points that follow the RFC will decline connections among other misery that it causes..

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  2. Erik Fair has answered this extensively over at Quora:

    The keyboard of the Teletype (TTY) ASR-33 (a very common terminal interface of the period from whence this standard hails) doesn't have underscore on it: http://www.pdp8.net/asr33/pics/k... which gives one a nasty problem: how do you type (input) a hostname if the hostname in question contains a character that your terminal interface can't generate?

    In the article a few more links are mentioned.

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  3. Microsoft Windows does not prohibit the underscore in the name of a computer. Some system administrators, either not knowing or not caring about RFC952, use underscores in the name of a computer that is connected to the internet, and either put this name in the DNS explicitly or allow it to be published via dynamic DNS.

    There's nothing particularly strange about these names. Examples might be JOHNS_COMPUTER or ACCOUNTING_DEPT_PC1.

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