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Q. When registering PTR records in reverse zone, how should I describe Name? (IPv4 edition)

How to describe Name varies depending on the IP address space for using reverse zones. Refer to the following for each case.

  • When the IP address space is "not /16"
    Describe only the last 1octet part of the IP address to be registered with the PTR record.


    		 IP address space to use Contract Zone Name IP address to be registered with the PTR record Number to be described in Name Notes
    1 192.0.2.0/24 2.0.192.in-addr.arpa. 192.0.2.41 41 (Last 1octet part of "IP address to be registered with the PTR record")
    *Do not add a dot (.) to the end of Name.
    2 192.0.2.40/29 040a.2.0.192.in-addr.arpa. The contract zone name on the left is an example of the reverse zone name of IP address space assigned by IIJ which is narrower than /24.
    3 192.0.2.40/29 40.2.0.192.in-addr.arpa.

    The contract zone name on the left is an example of the reverse zone name of IP address space assigned by a company other than IIJ.

    For details on what the actual reverse zone name will be, contact the business operator that has assigned the IP address space.

    As "41" is registered in Name as shown in the above example, the contract zone name (*part written in bold) is automatically complemented by the system as shown below.


    		 PTR records to be registered
    1 41.2.0.192.in-addr.arpa. IN PTR xxxxx.example.jp.
    2 41.040a.2.0.192.in-addr.arpa. IN PTR xxxxx.example.jp.
    3 41.40.2.0.192.in-addr.arpa. IN PTR xxxxx.example.jp.

  • When the IP address space is "/16"
    Describe the last 2octet parts of the IP address to be registered with the PTR record in reverse order.
    When the IP address space to be used is "192.168.0.0/16" and the PTR record is registered for "192.168.1.250," write only "250.1" in Name.

    IP address space to use Contract Zone Name IP address to be registered with the PTR record Number to be described in Name
    192.168.0.0/16 168.192.in-addr.arpa. 192.168.1.250 250.1 (Last 2octet parts of "IP address to be registered with the PTR record" that are described in reverse order)
    *Do not add a dot (.) to the end of Name.

    As "250.1" is registered in Name as shown in the above example, the contract zone name (*part written in bold) is automatically complemented by the system as shown below.

    PTR records to be registered
    250.1.168.192.in-addr.arpa. IN PTR xxxxx.example.jp.