[hackers] Re: [eric_AT_faurot.net: Re: problem with gethostbyaddr() on OBSD 5.4?]

From: Joerg Jung <mail_AT_umaxx.net>
Date: Thu, 6 Feb 2014 12:23:53 +0100

Am 05.02.2014 um 17:20 schrieb Stuart Henderson <stu_AT_spacehopper.org>:

> On 2014/02/05 11:10, Simon Perreault wrote:
>> Le 2014-02-05 03:33, Eric Faurot a écrit :
>>> Just a question before I commit it. The '/' character is apparently
>>> used in dname labels sometimes. Can anyone think of other chars that
>>> should be allowed too? Or do we want to be even more lenient wrt dname
>>> validation?
>> Why validate at all? Strictly speaking, all bytes are allowed in DNS
>> labels...
> Right - the usual restriction "letters, digits or hyphens" is on host
> names only, not DNS labels.

I do not think so. As stated in

The DNAME target is a domain name as defined in
http://tools.ietf.org/search/rfc1035 Section 2.3.1

> https://tools.ietf.org/html/rfc6672#section-6.2
> The advisory remarks in [RFC2317] concerning the choice of the "/"
> character apply here as well.

Yes, but only for _reverse_ delegations.

> https://tools.ietf.org/html/rfc2317 (section 4)
> Some DNS implementations are not kind to special characters in domain
> names, e.g. the "/" used in the above examples. As [3] makes clear,
> these are legal, though some might feel unsightly. Because these are
> not host names the restriction of [2] does not apply. Modern clients
> and servers have an option to act in the liberal and correct fashion.
> [3] https://tools.ietf.org/html/rfc2181#section-11

This one is obsolete and updated by others.

> " The DNS itself places only one restriction on the particular labels
> that can be used to identify resource records. That one restriction
> relates to the length of the label and the full name. The length of
> any one label is limited to between 1 and 63 octets. A full domain
> name is limited to 255 octets (including the separators). The zero
> length full name is defined as representing the root of the DNS tree,
> and is typically written and displayed as ".". Those restrictions
> aside, any binary string whatever can be used as the label of any
> resource record. "
Received on Thu Feb 06 2014 - 12:23:53 CET

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