[Dnsmasq-discuss] autogenerating dns records

Vladislav Grishenko themiron at mail.ru
Thu Apr 25 11:38:38 BST 2013

> From: Simon Kelley [mailto:simon at thekelleys.org.uk]
> Sent: Thursday, April 25, 2013 4:18 PM
> I'm not clear what the advantage is.

The main advantage is to have automatic reverse PTR records for the
subnet(s) for online services that check it (ftp, irc, etc). While IPv4 is
quite ok to pre-generate, it's quite impossible/inefficient for IPv6 SLAAC
subnet(s). Mean intended to be viewable, but not to be reused by human
offen. There're already tools to force readable names in dnsmasq/hosts, this
is about autogeneration only.

> The maximum length of the presentation
> form of an IPv6 address is 46 characters, which fits in a DNS label (63
> quite comfortably.

A matter of taste, I'd say. Full IPv6 reverse PTR representation plus domain
could not fit format (example: IRC server names name!name at host, where host
is reverse looked-up name) 

> By encoding the address, that makes it useless for
> humans, which is the main point of doing this, plus you'd have to support
> encoded form in forward as well as reverse queries, since people will do a
> reverse query and then use the result in a forward query later.

Actually not, since IPv6 address (with zero comp) could be more readable
(mean short), than expanded one plus domain. As wrote above, main aim - to
have reverse PTR records without pregeneration for services, not for humans,
also it's kind of masking.

> You've reminded me however that the prefix is limited to 63-46 for IPv6,
> be sure to avoid the label length limit.

The problem is it's artificial limit, one can use private prefix even with
/3 or less.

Best Regards, Vladislav Grishenko

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