Only for contracts which were automatically transferred from the old DNS Outsourcing Service or old DNS Secondary Service to this service, you can also use the name server host names (dns-a.iij.ad.jp, dns-b.iij.ad.jp, and dns-c.iij.ad.jp) which used to be provided by the old service. Moreover, when changing name servers registered with a higher zone and NS records in the zone to host names of the Managed DNS Server, the host names provided by the old service can be deleted without any impact.
After such host names have been deleted, name resolution should be performed by the Managed DNS Server which is registered newly with the name server.

Incidentally, when you use a host name of the name server provided by the old service, the availability of the service will stay at the same level as that of the old service.
The availability of the IIJ Managed DNS Service is higher than that of the old service. It is strongly recommended that you change the name server registered with the higher zone to the Managed DNS Server name, so that you can make the maximum use of the functions of this service.

• Refer to "Service Overview" for the availability of the IIJ Managed DNS Service.
• Refer to "IIJエンジニアブログ: https://eng-blog.iij.ad.jp/archives/5720" (Japanese Only) for differences in availability between the old and new services.