A signpost to support IPv6

Reverse lookup is used in various places. For example, sshd and inetd often reverse lookup when accepting a connection. I don't think there are many people who use host name authentication by relying on reverse lookup, but it is used in various ways, such as being output to the log.

Furthermore, connection processing may take a long time if reverse lookup settings do not exist,for example, "It takes a long time to log in". It is possible.

APNIC's mistakes"Reverse lookup is broken"There have been several cases in the past,At that time, one of the screams that came up on the JANOG mailing list was There was a case that login was not possible because access restrictions were registered by domain name in /etc/hosts.allow.

As you can see, reverse lookup can affect various things, but with IPv6, it may be difficult to set up reverse lookup for all IP addresses. As a result, the situation "Reverse lookup settings cannot be performed"has occurred.

In IPv6, users may not know in advance what kind of IPv6 address they will use.

In the IPv6 standard specification, the upper 64-bit network address and the lower 64-bit generated from the EUI-64-based hardware address are used to create an IPv6 address for each user's device. The client PC may periodically change the IPv6 address for privacy protection(*⁠)⁠.

Japanese ISPs often pre-register a unique host name for the IPv4 address assigned to users. If you issue a /64 address, there is a possibility that 2^64 addresses will be used.It is difficult to statically register reverse lookups for all addresses in advance.