named question

Andy Bradford amb-plugg at bradfords.org
Thu Sep 19 12:07:38 MDT 2013


Thus said Dan Egli on Thu, 19 Sep 2013 13:36:05 +0530:

> How  does the  name  service  daemon (named)  know  that, for  example
> address 192.168.2.11  resolves to the 0.168.192.in-addr.arpa  net used
> in reverse resolution?

First, DNS doesn't  have any knowledge of IP address  subnets and subnet
masks.

DNS  works with  names (organized  in zones).  11.2.168.192.in-addr.arpa
is  just  another name.  Because  DNS  doesn't  know anything  about  IP
addresses, all you are left with are names and delegations of subdomains
of  those  names.  Which  means  that   a  DNS  request  for  a  PTR  of
11.2.168.192.in-addr.arpa  will be  found  somewhere  in the  delegation
chain:

from root to .arpa
from .arpa to in-addr.arpa
from in-addr.arpa to 192.in-addr.arpa
from 192.in-addr.arpa to 168.192.in-addr.arpa
from 168.192.in-addr.arpa to 2.198.192.in-addr.arpa

This  means  that  your  question is  most  likely  framed  incorrectly.
Under  normal  configurations  the   ``reverse  DNS  for  192.168.2.11''
will  not  be  found in  0.168.192.in-addr.arpa.  0.168.192.in-addr.arpa
can   only    delegate   subdomains   of    0.168.192.in-addr.arpa   and
11.2.168.192.in-addr.arpa is not  a subdomain of 0.168.192.in-addr.arpa.
The authority for 168.192.in-addr.arpa, on the other hand, would be able
to answer/delegate queries for 11.2.168.192.in-addr.arpa.

Of course,  it is  possible to make  PTRs for  2.168.192.in-addr.arpa be
found in  0.168.192.in-addr.arpa, but this  would require someone  to go
out of their way to make it work this way.

Hope this helps. If not, feel free to ask for clarification.

Andy
--
TAI64 timestamp: 40000000523b3d88


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