The ISP modem restart at 08:19 re-delegated the same /64 five seconds
after the PPPoE drop. networkd re-announced it at once, but the fixed
7 s radvd run kept sending preferred-lifetime-0 RAs for it, so clients
sat on a deprecated prefix until networkd's next periodic RA and IPv6
stayed broken for minutes.
Send one RA per radvd start, up to three 3 s apart, and skip each one if
the /64 is already back on the interface. Verified on stellio with the
rendered script: a prefix gone for good -> three RAs; the PD address
removed and re-added 4 s later -> two RAs, then "is back, leaving it
announced", client preferred again and pinging over v6.
kurogeek
7f3457859e