Text 1164, 50 rader
Skriven 2008-03-21 06:42:54 av andrew clarke (3:633/267)
   Kommentar till text 1160 av Michiel van der Vlist (2:280/5555)
Ärende: Proper nodelist format for Internet-only nodes?
=======================================================
On Thu, 20 Mar 2008 05:06:12 +0100 "Michiel van der Vlist -> Alexey
Vissarionov" <2:280/5555> wrote:

>   MV>> 0..9, '.', '-', '_'.
>
>   AV> Bug - 0x5F ('_') is not permitted in host or domain names.
>
> Are you sure? I thought it was merely a recommendation not to use it
> rather than an absolute. Underlines in host names can be confusing
> because many applications underline clickable links. That makes it
> difficult to disctinyush between a spaceand an underline.
>
> I may be wrong...

http://en.wikipedia.org/wiki/Host_name#Restrictions_on_valid_host_names

Restrictions on valid host names

Hostnames, like all domain names[1], are made up of a series of
"labels", with each label being separated by a dot. Each label must be
between 1 and 63 characters long, and there is a maximum of 255
characters when all labels are combined.

Unlike domain names, hostname labels can only be made up of the ASCII
letters 'a' through 'z' (case-insensitive), the digits '0' through '9',
and the hyphen. Labels cannot start nor end with a hyphen. Special
characters other than the hyphen (and the dot between labels) are not
allowed, although they are sometimes used anyway. Underscore characters
are commonly used by Windows systems but according to RFC 952 they are
not allowed and several systems, such as DomainKeys and the SRV record
deliberately use the underscore to make sure their special domain names
are not confused with a hostname. Since some systems will check to make
sure that hostnames contain only valid characters and others do not,
the use of the invalid characters such as the underscore has caused
many subtle problems in systems that connect to the wider world.

So, the hostname "en.wikipedia.org" is made up of the DNS labels "en",
"wikipedia" and "org". Labels such as "2600" and "3com" can be used in
hostnames, but "-hi-" and "*hi*" are invalid.

A hostname is considered to be a fully qualified domain name (FQDN) if
all the labels up to and including the top-level domain name (TLD) are
specified. Depending on the system, an unqualified hostname such as
"compsci" or "wikipedia" may be combined with default domain names in
order to determine the fully qualified domain name. So, a student at
Harvard may be able to send mail to "joe@compsci" and have it sent to
compsci.harvard.edu.

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