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Knowledgebase:
RFC2317 - Classless Reverse DNS Delegation
Posted by Nick Rose, Last modified by Nick Rose on 30 December 2013 07:53 PM

RFC2317 uses a similar looking naming scheme to RFC4183, but an important difference exists. Your zone name starts with the last octet of your network IP address, followed by a hyphen, then the last octet of your broadcast address, then the rest of the usual three-octets.in-addr.arpa notation.

This method is covered in section 9.5.2.2 of O'Reilly's "DNS & Bind", 3rd Edition.

If you were allocated 172.31.15.144/28:

  • 172.31.15.144 is the network IP.
  • 172.31.15.159 is the broadcast IP

You would therefore name your zone file:

144-159.15.31.172.in-addr.arpa.

Your PTR records would look the same as the previous examples:

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 144-159.15.31.172.in-addr.arpa.

# dig 144-159.15.31.172.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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 rfc2317.txt (17.33 KB)

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