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Church Of The
Swimming Elephant

2.1 Host Names and Numbers Connected: An Internet Encyclopedia
2.1 Host Names and Numbers

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2.1 Host Names and Numbers

2.1 Host Names and Numbers

The syntax of a legal Internet host name was specified in RFC-952 [DNS:4]. One aspect of host name syntax is hereby changed: the restriction on the first character is relaxed to allow either a letter or a digit. Host software MUST support this more liberal syntax.

Host software MUST handle host names of up to 63 characters and SHOULD handle host names of up to 255 characters.

Whenever a user inputs the identity of an Internet host, it SHOULD be possible to enter either (1) a host domain name or (2) an IP address in dotted-decimal ("#.#.#.#") form. The host SHOULD check the string syntactically for a dotted-decimal number before looking it up in the Domain Name System.


This last requirement is not intended to specify the complete syntactic form for entering a dotted-decimal host number; that is considered to be a user-interface issue. For example, a dotted-decimal number must be enclosed within "[ ]" brackets for SMTP mail (see Section 5.2.17). This notation could be made universal within a host system, simplifying the syntactic checking for a dotted-decimal number.

If a dotted-decimal number can be entered without such identifying delimiters, then a full syntactic check must be made, because a segment of a host domain name is now allowed to begin with a digit and could legally be entirely numeric (see Section However, a valid host name can never have the dotted-decimal form #.#.#.#, since at least the highest-level component label will be alphabetic.

Next: 2.2 Using Domain Name Service

Connected: An Internet Encyclopedia
2.1 Host Names and Numbers


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