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I’m trying to setup a reverse zone file for this subnet that has two hosts on it: 10.10.100.10 and 10.128.5.10. This means he netmask for the subnet would be 255.0.0.0. I inferred that the file name would be 10.in-addr.arpa, but reading the specification docs, it seems as though the reverse zone file is only going to allow for one byte to express each host. This leads me to believe that the subnet needs to be 24-bit--never 8. Is that true?

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  • What DNS server are you using? May 12, 2014 at 16:18
  • I'm doing this on RHEL4 and their bind package is bind-9.2.4
    – Angus
    May 12, 2014 at 16:57

1 Answer 1

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The reverse DNS record for an IP address will always be like:

10.5.128.10.in-addr.arpa.

At every dot you can delegate to another zone, if you want. So the zone for the whole 10.0.0.0/8 network the reverse is:

10.in-addr.arpa.

In this zone you can either have a PTR record like:

10.5.128.10.in-addr.arpa. IN PTR some.hostname.local.

Or if you want to delegate parts to other name servers (because you don't want to have everything on one set of servers, if responsibility of a part of the tree lies with another organisation or department etc.) you have a record like:

128.10.in-addr.arpa. IN NS some.dnsserver.local.

or

5.128.10.in-addr.arpa. IN NS some.dnsserver.local.

depending on if/how you want to delegate responsibility for parts of the reverse DNS tree to other name servers.

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