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Re: Inconsistency? (was: Anti-Spoofing Technology)

2005-04-17 17:57:10

On Sun April 17 2005 18:19, John P Baker wrote:

In RFC2821, a clear definition of the structure of a domain name is
provided.  In this definition, the length of a domain name may not exceed
255 characters, and consists of one (1) or more "labels", each separated
from the other by a period (".").  The length of each label may not exceed
63 characters.

So far, so good.

Each label must begin with an alphabetic character

No, "" is a valid domain name.

(case-insensitive) and must terminate with an alphabetic character (again,
case-insensitive) or with a decimal digit.  Characters internal to a label
may be alphabetic (again, case-insensitive), decimal digit, or hyphen ("-").


In RFC2822, the definition is more obscure, with the domain name character
set consisting of a much broader subset of ASCII.  Of particular concern is
the fact that in this RFC, ASCII character which have special meaning such
as "@" appear to be valid within a domain name.

2822 syntax was made general; actual content is determined by other

Does RFC2821 correctly reflect the syntactic requirements for domain names,
or is it too incorrect, and there exists some other RFC which specifically
addresses the issue?

2821 appears to be correct (note that labels may begin with a letter
or digit).  The definitive DNS RFCs are 1034 and 1035, as amended by

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