ANAME is an extended record type unique to this service.

According to the original DNS specifications, CNAME records cannot be placed at the zone apex (record having the same name as the zone name). You can use ANAME instead of CNAME in a case where you want to specify an external resource as a name, not as an IP address, for the zone apex.

Usage and restrictions

• You can set one ANAME only to the zone apex (record having the same name as the zone name).
• Use CNAME for records other than the zone apex.
• Because the load balancing function with DNS does not work for host names, such as CDN, for which DNS response changes dynamically, use of ANAME records is not recommended. Note that the same is true in a case where the host name specified by ANAME is CNAME and the canonical name of CNAME returns a dynamic response.

Link to primary/secondary name servers

• When you use this service as a secondary name server: Zones in which ANAME records are written cannot be transferred from your primary name server.
• When you use this service as the primary name server: Zones in which ANAME records are rewritten to A/AAAA records are transferred to your secondary name server.

Mechanism of the operation

Let’s assume that a value "aname.example.jp." is registered with the ANAME record of the zone apex in the name of "example.jp." in the description below.

• If no A/AAAA record exists in "aname.example.jp.", an empty response is returned to the inquiry to the A/AAAA record of "example.jp."
• When name resolution of "aname.example.jp." ends in error, the IPv4/v6 address obtained when name resolution succeeded last time continues to be used.
• If a record type other than A/AAAA record exists in "aname.example.jp.", only IPv4/IPv6 addresses registered with the A/AAAA record are responded for ANAME. It does not respond to record types other than A/AAAA record.
• If DNSSEC signing is enabled in "example.jp.", DNSSEC signing will be implemented and a response will be sent even when "aname.example.jp." is not DNSSEC signed and, strictly speaking, completeness cannot be guaranteed.
  
  • If you do not agree to the previously explained this behavior, please refrain from using ANAME.

IP address response

The IPv4/v6 address of "aname.example.jp." is the response returned to an inquiry of an A/AAAA record of "example.jp." When multiple IP addresses are set, up to 4 A and AAAA records each are captured.

Example: When ANAME is set to the apex of a zone name "example.jp."

When "aname.example.jp." is set with an NS or CNAME record as shown in the following example, the IPv4/v6 address is returned if any A/AAAA record exists in the delegation destination of "aname.example.jp." or "sub.aname.example.jp." of the canonical name.

Example: When "aname.example.jp" is set with an NS or CNAME record

TTL and update timing

• In this service, name resolution is performed for "aname.example.jp" specified by the ANAME record for each passage of the TTL value.
  • The name of "aname.example.jp." is not resolved at the timing of an inquiry to the A/AAAA record of "example.jp."
  • Unless A/AAAA records exist in "aname.example.jp.", the IP address information will not be retained and the TTL value set in <minttl> in the SOA record will be referenced for the next name resolution.
  • When "aname.example.jp." is set with an NS or CNAME record, the TTL value registered with the A/AAAA record is referenced if an A/AAAA record is found with the delegation destination or canonical name.
• The minimum check interval of name resolution is 30 seconds. If the TTL value is less than 30 seconds, update is checked at intervals of 30 seconds.
  
  • Note, however, that the update interval may be adjusted in cases other than the above case with the aim of protecting IIJ’s equipment and the authority DNS server of the check destination.