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frogstarr78
Asked: 2011-06-25 07:58:16 +0800 CST

Bind Zones split by octet

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Why are the reverse Zone files in Bind split by octets instead of subnets?

This is what I would expect to see:

subnets: 
  172.0.208/22
  10.0.2.0/25
  10.0.2.128/25

host# ls /path/to/zone/files
208.0.172.in-addr.arpa
0.2.0.10.in-addr.arpa
128.2.0.10.in-addr.arpa
domain-name-system bind domain reverse-dns subnet

2 Answers

  1. It is easiest to split on octect boundaries but see RFC2317 for "classless IN-ADDR.ARPA delegation." https://www.rfc-editor.org/rfc/rfc2317

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  2. Best Answer

    A query for 172.0.209.1 will be for a record at 1.209.0.172.in-addr.arpa, which isn't under the 208.0.172.in-addr.arpa zone. This is also why you can't have a reverse DNS delegation for a subnet smaller than /24, either; there's no ability or logic in the DNS standard to "split" the delegations for these zones into smaller chunks.

    DNS serves name data; it has no special logic built around serving data for subnets, so the standard for reverse zones conforms to the "DNS-looking" format of the dot-separated numbers.

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