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 notation.

If you were allocated

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

You would therefore name your zone file:

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

145 IN PTR

and so on.

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

Debugging Your Subnet Reverse DNS

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

# dig CNAME

Check to see if there is a CNAME record for the IP, using the zone

# dig 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).

 rfc4183.txt (17.93 KB)

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