Help test softupdates journaling (SUJ)
Chuck Swiger
cswiger at mac.com
Mon Jan 18 23:04:58 UTC 2010
On Jan 18, 2010, at 2:18 PM, Rink Springer wrote:
>> Because DNS hostnames can't contain underscores... ?
>
> That is false, they can (in fact, SVR records depend on this). However,
> Jeff's blog is at http://jeffr-tech.livejournal.com/; his username
> appears to be 'jeffr_tech'.
Underscores appear in SRV records for the explicit purpose of not conflicting with any valid hostname:
The format of the SRV RR
Here is the format of the SRV RR, whose DNS type code is 33:
_Service._Proto.Name TTL Class SRV Priority Weight Port Target
Service
The symbolic name of the desired service, as defined in Assigned
Numbers [STD 2] or locally. An underscore (_) is prepended to
the service identifier to avoid collisions with DNS labels that
occur in nature.
...from http://www.ietf.org/rfc/rfc2782.txt. See http://www.ietf.org/rfc/rfc952.txt
1. A "name" (Net, Host, Gateway, or Domain name) is a text string up
to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus
sign (-), and period (.).
...which was slightly modified by http://www.ietf.org/rfc/rfc1123.txt
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.
Regards,
--
-Chuck
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