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Knowledgebase:
RFC4183 - Reverse DNS Subdelegation
Posted by Nick Rose, Last modified by Nick Rose on 30 December 2013 07:54 PM

RFC4183, specifies rDNS for subnets. However, it is a more specific notation and allows for a wide range of delegation. The naming scheme starts with the last octet of your network IP, followed by a hyphen, followed by the netmask bits of your subnet, and ends with the usual three-octets.in-addr.arpa notation.

If you were allocated 172.31.15.144/28:

  • 172.31.15.144 is the network IP.
  • And /28 is the netmask bit number designating the size of your network.

You would therefore name your zone file:

144-28.15.31.172.in-addr.arpa.

Then you would have your PTR records like you would normally:

145 IN PTR somename.com.

and so on.

In this case we need the hostnames of your nameservers. We delegate the subnet in-addr.arpa zone to your nameservers using NS records.

Debugging Your Subnet Reverse DNS

If you were allocated 172.31.15.144/28 (this is a nonworking theoretical example), you would use the following commands to make sure we were pointing reverse to you:

# dig 144.15.31.172.in-addr.arpa. @ns1.scalabledns.com. CNAME

Check to see if there is a CNAME record for the IP, using the zone 144-28.15.31.172.in-addr.arpa.

# dig 144-28.15.31.172.in-addr.arpa. @ns1.scalabledns.com. NS

Check the name servers listed.

The first command checks to see what subnet we are pointing an IP in your range to (via a CNAME record) and the second checks where we say the DNS for that subnet is (via a NS record).



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 rfc4183.txt (17.93 KB)

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