You can manage reverse zones with the Managed DNS Service.

Checking Reverse Zone Names

Reverse zone names vary according to the IP address assigned.

For IPv4

• When the address range is /9 to /15
  • The range is divided into /16 ranges, and a reverse zone is set to each of them. You need to sign a contract for each zone.
    For "10.0.0.0/15," settings are configured with two zones: "0.10.in-addr.arpa" and "1.10.in-addr.arpa."
• When the address range is /16
  • For "a.b.0.0/16," the reverse zone name is "b.a.in-addr.arpa."
  • For "10.1.0.0/16," the reverse zone name is "1.10.in-addr.arpa."
• When the address range is /17 to /23
  • The range is divided into /24 ranges, and a reverse zone is set to each of them. You need to sign a contract for each zone.
  • For "10.1.2.0/22," settings are configured with four zones: "0.2.1.10.in-addr.arpa," "1.2.1.10.in-addr.arpa," "2.2.1.10.in-addr.arpa," and "3.2.1.10.in-addr.arpa."
• When the address range is /24
  • For "a.b.c.0/24," the reverse zone name is "c.b.a.in-addr.arpa."
  • For "10.1.2.0/24," the reverse zone name is "2.1.10.in-addr.arpa."
• When the address range is /25 to /32
  • Reverse zone names differ from one IP address assignment organization to another.
  • For "a.b.c.d/n" which is an address range assigned by IIJ, the reverse zone name is "ddda.c.b.a.in-addr.arpa." "ddda" consists of a three-digit number and "a." If the number is a one-digit or two-digit number, prepose the number with "0." There is no need to prepose with "0" for any other cases. For "10.1.2.64/29," the reverse zone name is "064a.2.1.10.in-addr.arpa."
  • For reverse zone names of address ranges assigned by an organization other than IIJ, contact the organization in question.

For IPv6

This section uses "2001:db8:12:3400::/56" as an example of the assigned address.

1. Convert the address part (2001:db8:12:3400::) into an unabbreviated form.
   2001:0db8:0012:3400:0000:0000:0000:0000
2. Divide the range part (56) by 4.
   56/4=14
3. Remove the colons (:) starting from the left of the string obtained in procedure (1), and take away as many characters as the number obtained in procedure (2) from the string.
   20010db8001234
4. Arrange the string obtained in procedure (3) in reverse order, and separate each character with a dot (.).
   4.3.2.1.0.0.8.b.d.0.1.0.0.2
5. The reverse zone name is a string formed by adding ".ip6.arpa" to the end of the string obtained in procedure (4).
   4.3.2.1.0.0.8.b.d.0.1.0.0.2.ip6.arpa

Contracting Reverse Zones

Sign up for the reverse zone names you have checked in "Checking reverse zone names" with the DNS Management Service. The contract procedure is the same as that for forward zones. Refer to "Applications and Procedures" for more information.

Setting Reverse Zones

You will need to set the reverse zones for which you have signed up. The methods for setting reverse zones include a method for configuring the settings from the control panel and a method for transferring zones from the primary name server that you have prepared, which are basically the same as the methods for setting forward zones.
To set reverse zones, decide on an operational procedure and use the following pages as a reference according to your form of utilization.

• Operating DNS with Managed DNS Servers Only
• Operating a Managed DNS Server as a Secondary Name Server
• Operating a Managed DNS Server as the Primary Name Server

You can configure zone settings even before the utilization start date (the zone status is "Unpublished").

For IPv4

When the address range is a value other than from /25 to /32, if the IP address is "a.b.c.d," the reverse lookup name is "d.c.b.a.in-addr.arpa.". For "10.1.2.3," the reverse lookup name is "3.2.1.10.in-addr.arpa".

When the address range is a value from /25 to /32, the reverse lookup name is "(Last octet of the IP address).(Reverse zone name)." Because the reverse zone name for "10.1.2.0/29," an address range assigned by IIJ, is "000a.2.1.10.in-addr.arpa.", when the IP address is "10.1.2.3," the reverse lookup name is "3.000a.2.1.10.in-addr.arpa.". For reverse zone names of address ranges assigned by an organization other than IIJ, contact the organization in question.

For IPv6

For "2001:db8:12:3400::5," the reverse lookup name will be as shown below.

1. Convert the IP address into an unabbreviated form.
   2001:0db8:0012:3400:0000:0000:0000:0005
2. Arrange the characters other than colons (:) in reverse order, and separate each character with a dot (.).
   5.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.4.3.2.1.0.0.8.b.d.0.1.0.0.2
3. Add ".ip6.arpa." to the end.
   5.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.4.3.2.1.0.0.8.b.d.0.1.0.0.2.ip6.arpa.

If you can use the arpaname command for an OS such as Linux, the reverse lookup name can also be obtained by executing "arpaname IPaddress."

Registering Name Servers

Use "Registering and Changing Name Servers" as a reference to apply for a change to the NS record with the IP address assignment organization.