radvd binary package in Ubuntu Focal arm64

 IPv6 has a lot more support for autoconfiguration than IPv4. But
 for this autoconfiguration to work on the hosts of a network, the
 routers of the local network have to run a program which answers
 the autoconfiguration requests of the hosts.
 .
 On Linux this program is called radvd, which stands for Router
 ADVertisement Daemon. This daemon listens to router solicitations (RS)
 and answers with router advertisement (RA). Furthermore unsolicited
 RAs are also sent from time to time.

Source package