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Reverse DNS Zones

You can easily host reverse DNS with NS1 for both IPv4 and IPv6 subnets.

To configure reverse DNS for an IPv4 subnet, you need to create a new reverse zone for the subnet. Suppose you want to host reverse DNS for the 1.2.3.0/24 subnet:

  1. Create a zone with the domain 3.2.1.in-addr.arpa
  2. Within the zone, create records for each IP of type PTR, with the answer being the name associated with the IP. For example, create a record like 4.3.2.1.in-addr.arpa/PTR with name my.hostname.com if you want a reverse lookup of 1.2.3.4 to resolve to my.hostname.com.
  3. If you are the owner of the subnet, change the delegation of the reverse DNS with your RIR (e.g., ARIN, RIPE, etc) to point to the DNS servers assigned to your reverse zone (shown in the left panel on your zone's configuration page in the NS1 portal).

To configure reverse DNS for an IPv4 subnet smaller than a /24, say, a /29, the owner of the IP space (e.g., your hosting provider) will need to sub-delegate a reverse zone on your behalf. You'll need to work with them directly to do so. In general, they will subdelegate a zone with a name like 0/29.3.2.1.in-addr.arpa, or 0-29.3.2.1.in-addr.arpa. NS1 allows you to create zones in either format. The steps are:

  1. Ask your provider which format ("/" or "-") they will use, and then create the zone as instructed
  2. Within the zone, create records for each IP of type PTR -- for example, 4.0/29.3.2.1.in-addr.arpa/PTR to provide a reverse name for 1.2.3.4 when the 1.2.3.0/29 network has been sub-delegated.
  3. Give your provider the DNS servers assigned to your reverse zone by NSONE (shown in the left panel on the zone's configuration page) so they can enact the sub-delegation.

Configuring reverse DNS for an IPv6 subnet is similar -- if you have been directly assigned the IPv6 space by a RIR, you can delegate the reverse DNS to NS1 yourself; if not, you will need to work with your provider to sub-delegate the reverse DNS.

IPv6 reverse domains look like c.b.a.9.8.7.6.5.4.3.2.1.ip6.arpa (for a /44) and can extend further for smaller subnets. Follow the same process as with IPv4 for creating a reverse zone, PTR records in the zone, etc.