Potential pitfalls in DNS handling [LWN.net]

Potential pitfalls in DNS handling

Posted Nov 15, 2012 17:05 UTC (Thu) by RobSeace (subscriber, #4435)
Parent article: Potential pitfalls in DNS handling

Many believe that domain and host names are restricted to certain subsets of characters, but that is not true. As RFC 2181 specifies, the limits are purely length-based (63 octets per component, 255 octets for a domain name). Each octet of the name can contain any value from 0 to 255.

Talking purely of DNS restrictions, sure... But, people get their beliefs about actual hostname restrictions from RFC 1123 and RFC 952 before it, which limit host and domain names to "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'."

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