Skip site navigation (1)Skip section navigation (2)
Date:      Fri, 28 Feb 1997 16:37:17 -0800 (PST)
From:      Dan Busarow <dan@dpcsys.com>
To:        Adrian Gonzalez <agonzalez@starbase.globalpc.net>
Cc:        freebsd-isp@FreeBSD.ORG
Subject:   Re: DNS question
Message-ID:  <Pine.UW2.3.95.970228160757.16033F-100000@cedb>
In-Reply-To: <Pine.BSF.3.91.970228162710.15168A-100000@starbase.globalpc.net>

next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, 28 Feb 1997, Adrian Gonzalez wrote:
> I need to set up 2 different domain in the same class C network, but in 
> different subnets... for example (these are not the real addresses, of 
> course)
> 
> 128.1.2.0  to 128.1.2.31 - first subnet
> 128.1.2.32 to 128.1.2.63 - second subnet
> 
[ ...]
>
> What would the reverse entries look like?
> 
> primary		2.1.128.in-addr.arpa	foo.rev  (??)

primary	2.1.128.in-addr.arpa	db.128.1.2

Using my preferred naming, the zone is for the address space,
not the domain.

In the reverse files you need to have an entry for the name servers
you are delegating subnet space to like:

0      IN  NS  ns.foo.com.
32     IN  NS  ns.bar.com.

These are *not* the addresses of the name servers, this says that
the 0 subnet has name server ns.foo.com and the 32 subnet has name 
server ns.bar.com.

Now comes the fun part.  For *every* delegated IP address you need 
entries like this:

1       CNAME   1.0.2.1.128.in-addr.arpa.
2       CNAME   2.0.2.1.128.in-addr.arpa.
3       CNAME   3.0.2.1.128.in-addr.arpa.
4       CNAME   4.0.2.1.128.in-addr.arpa.
5       CNAME   5.0.2.1.128.in-addr.arpa.
6       CNAME   6.0.2.1.128.in-addr.arpa.

See how we gave them an extra octet?  Actually, since these are
domain names, not IP addresses, we have just added another level to
the domain.  So when I do a reverse lookup on 128.1.2.1 BIND does this

1) get the CNAME 1.0.2.1.128.in-addr.arpa
2) drop the left most part of the domain name and get 0.2.1.128.in-addr.arpa.
3) lookup 0.2.1.128.in-addr.arpa and get the NS entry pointing at ns.foo.com.
4) direct the query to ns.foo.com

The reverse files ns.foo.com maintains look normal, ie

1	IN PTR	ns.foo.com.
2	IN PTR	mail.foo.com.


For addresses outside of the delegated portion (64-255 here) you have
normal entries.  If you are reserving this C for subnets only (good
idea) then the only entries you would need would be for your side
of any gateways.

If you get a customer who needs a subnet but can't (won't) handle
reverse DNS (Macs can't) then you maintain their entries in the same file
with "normal" PTR records.

For a full discussion see draft-ietf-cidrd-classless-inaddr-01.txt
at your favorite IETF draft repository.

Dan
-- 
 Dan Busarow                                                  714 443 4172
 DPC Systems / Beach.Net                                    dan@dpcsys.com
 Dana Point, California  83 09 EF 59 E0 11 89 B4   8D 09 DB FD E1 DD 0C 82




Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.UW2.3.95.970228160757.16033F-100000>