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:
You would therefore name your zone file:
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 188.8.131.52.in-addr.arpa. @ns1.scalabledns.com. CNAME
Check to see if there is a CNAME record for the IP, using the zone 144-184.108.40.206.in-addr.arpa.
# dig 144-220.127.116.11.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).