in-addr.arpa reverse lookup db files w/ Class B subnet

Kevin Darcy kcd at daimlerchrysler.com
Thu Feb 3 21:17:42 UTC 2000


First of all, I realize that you're setting this up on a private LAN, but the
"real" intranet.org belongs to someone I know (a former member of the local
user group), and I think it's still an active site. If you ever, e.g. set up an
Internet mail gateway and you want to send mail to *that* intranet.org, you're
likely to have problems, because of the naming ambiguity you've created. Before
you get too far, you might want to consider a different name.

As to the question you asked... DNS doesn't really know anything about network
"classes"; it just structures the in-addr.arpa tree on octet boundaries. So you
could set up the 172.16/16 as either one *.16.172.in-addr.arpa zone for each
/24 of it that you're using, or just throw everything into a single
16.172.in-addr.arpa zone, or a combination of both, i.e. 16.172.in-addr.arpa
containing delegations to some number of /24's. For that matter, you could
create just a single 172.in-addr.arpa (or a single in-addr.arpa!) which
contained *all* of your PTR's. For small, isolated "toy" networks, I've been
known to put *everything* -- forward and reverse -- into a single root
zone! It's all up to you. All that really matters is that when a PTR query
comes in for xx.xx.16.172.in-addr.arpa, named finds it and returns the answer.


- Kevin


Phil Olson wrote:

> Hello,
> I am trying to setup an Intranet on my LAN with a single zone
> (intranet.org.), and am trying to determine what my db files should look
> like.  I have 2 subnets, 172.16.0.0/16, and 172.17.1.0/24.  What I am not
> sure about is how the reverse mapping files (in-addr.arpa.) should look
> like.  Here is my first attempt at the following files: db.intranet,
> db.172.16, and db.172.17.1.  What I am not sure on is: since my first subnet
> is a full class B, should the file be named db.172.16, or db.172.16.0?  And
> inside of that file, should the PTR record for 172.16.0.10 read
> 10 IN PTR mail.intranet.org.
>
> OR
>
> 0.10 IN PTR mail.intranet.org.  ?
>
> I looked in the dns and bind book from O'Reilly but it only had examples of
> subnets with a /24 mask.  Thanks in advance.
>
> -Phil
>
> ; file db.intranet
> @ IN SOA ns1.intranet.org. hostmaster.mail.intranet.org. (
>    1 ; Serial
>    10800 ; Refresh after 3 hours
>    3600 ; Retry after 1 hour
>    604800 ; Expire after 1 week
>    86400 ) ; Minimum TTL of 1 day
>
> ; Name Servers
>  IN NS ns1.intranet.org.
>  IN NS ns2.intranet.org.
>
> ; Addresses for the canonical names
> localhost IN A  127.0.0.1
> mail  IN A  172.16.0.10
> home  IN A  172.16.0.16
> ns1  IN A  172.16.0.17
> ns2  IN A  172.16.0.18
> smtp  IN A  172.17.1.4
> web  IN A  172.17.1.5
>
> ; MX Records
> intranet.org. IN MX 10 mail.intranet.org.
>
> ; file db.172.16
> @ IN SOA ns1.intranet.org. hostmaster.mail.intranet.org. (
>   1 ; Serial
>   10800 ; Refresh after 3 hours
>   3600 ; Retry after 1 hour
>   604800 ; Expire after 1 week
>   86400 ) ; Minimum TTL of 1 day
>
> ; Name Servers
>  IN NS ns1.intranet.org.
>  IN NS ns2.intranet.org.
>
> ; Addresses point to canonical name
> 10 IN PTR mail.intranet.org.
> 16 IN PTR home.intranet.org.
> 17 IN PTR ns1.intranet.org.
> 18 IN PTR ns2.intranet.org.
>
> ; file db.172.17.1
> @ IN SOA ns1.intranet.org. hostmaster.mail.intranet.org. (
>   1 ; Serial
>   10800 ; Refresh after 3 hours
>   3600 ; Retry after 1 hour
>   604800 ; Expire after 1 week
>   86400 ) ; Minimum TTL of 1 day
>
> ; Name Servers
>  IN NS ns1.intranet.org.
>  IN NS ns2.intranet.org.
>
> ; Addresses point to canonical name
> 4 IN PTR smtp.intranet.org.
> 5 IN PTR web.intranet.org.






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