Slipeer 17 мар 2013 в 00:07

Так что это за «грозная» точка на конце доменного имени?

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Так что это за «грозная» точка на конце доменного имени? — возник у некоторых вопрос, после недавнего поста.
Кто не знает и хочет узнать — добро пожаловать под хабракат — смахнём пыль с RFC четвертьвековой давности и проведём маленькое собственное расследование.

На самом деле с этой точкой всё просто.
Согласно RFC 1034 (см. $3.1 стр.7)

 ...Since a complete
domain name ends with the root label, this leads to a printed form which
ends in a dot.  We use this property to distinguish between:

   - a character string which represents a complete domain name
     (often called "absolute").  For example, "poneria.ISI.EDU."

   - a character string that represents the starting labels of a
     domain name which is incomplete, and should be completed by
     local software using knowledge of the local domain (often
     called "relative").  For example, "poneria" used in the
     ISI.EDU domain.</blockquote>

То есть точка в конце доменного имени указывает, что это полное доменное имя (FQDN). Если точки нет — значит имя относительное. Кому приходилось конфигурировать DNS сервера — видел эту точку в файлах зон.

Так почему же в адресных строках браузеров мы всюду наблюдаем доменные имена без точки на конце?
Формат Uniform Resource Locators (URL) документирован в 1994г. в RFC 1738 (см. $3.1 стр.5 )

 
host
        The fully qualified domain name of a network host, or its IP
        address as a set of four decimal digit groups separated by
        ".". Fully qualified domain names take the form as described
        in Section 3.5 of RFC 1034 [13] and Section 2.1 of RFC 1123
        [5]: a sequence of domain labels separated by ".", each domain
        label starting and ending with an alphanumerical character and
        possibly also containing "-" characters. The rightmost domain
        label will never start with a digit, though, which
        syntactically distinguishes all domain names from the IP
        addresses.

То есть host — всегда либо FQDN либо ip — другого стандарт не предусматривает.

Как видите тут идёт ссылка на секцию 3.5 RFC 1034, но в секции 3.5 описывается предпочтительный синтаксис DNS имён

RFC 1034 3.5 Preferred name syntax

3.5. Preferred name syntax

The DNS specifications attempt to be as general as possible in the rules
for constructing domain names.  The idea is that the name of any
existing object can be expressed as a domain name with minimal changes.
However, when assigning a domain name for an object, the prudent user
will select a name which satisfies both the rules of the domain system
and any existing rules for the object, whether these rules are published
or implied by existing programs.

For example, when naming a mail domain, the user should satisfy both the
rules of this memo and those in RFC-822.  When creating a new host name,
the old rules for HOSTS.TXT should be followed.  This avoids problems
when old software is converted to use domain names.

The following syntax will result in fewer problems with many
applications that use domain names (e.g., mail, TELNET).

<domain> ::= <subdomain> | " "

<subdomain> ::= <label> | <subdomain> "." <label>

<label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]

<ldh-str> ::= <let-dig-hyp> | <let-dig-hyp> <ldh-str>

<let-dig-hyp> ::= <let-dig> | "-"

<let-dig> ::= <letter> | <digit>

<letter> ::= any one of the 52 alphabetic characters A through Z in
upper case and a through z in lower case

<digit> ::= any one of the ten digits 0 through 9

Note that while upper and lower case letters are allowed in domain
names, no significance is attached to the case.  That is, two names with
the same spelling but different case are to be treated as if identical.

The labels must follow the rules for ARPANET host names.  They must
start with a letter, end with a letter or digit, and have as interior
characters only letters, digits, and hyphen.  There are also some
restrictions on the length.  Labels must be 63 characters or less.

For example, the following strings identify hosts in the Internet:

A.ISI.EDU  XX.LCS.MIT.EDU  SRI-NIC.ARPA

и нет ни строчки про финальную точку в fqdn

Вот тут, видимо, точка и потерялась…

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Так что это за «грозная» точка на конце доменного имени?

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