DNSUp is an RFC2136-compliant dynamic DNS updater that harvests addresses from interfaces, merging them with partial addresses specified in a configuration file. It’s intended to be used to keep dynamic DNS entries up-to-date when your ISP will only issue you a dynamic IPv6 prefix.
DNS no longer offers an official record type that supports IPv6 address chaining, where a single RR could contain the suffix-part of an IPv6 address and allow a parent record (or multiple parent records) to fill in its prefix.
Because of that, any dynamic update payload containing an IPv6 address must contain the entire IPv6 address (AAAA record). This is typically (in SLAAC/RA configurations) known only to the host, which makes it somewhat difficult to construct a single record for that host if you want to expose its address via dynamic update.
Through a combination of DHCPv6 and DNSUp, you can publish a complete AAAA record for any host based on a prefix from an originating interface and a suffix specified for that host in your config file.
: As of RFC6563, the
A6 record type
is officially deprecated.