After the reboot vlan-lan got its /64 at boot, but IPv6 still failed for
clients: the first PPPoE session lands on another AIS BNG, is torn down
minutes later, and the reconnect brings a different /64 (07:53
2405:9800:b911:91e3 -> 07:57 b910:1f5d). networkd announces the new
prefix at once but never deprecates the old one (systemd#29651), so
clients keep it preferred for up to 30 minutes and source selection
sends every connection from a dead address.
router-radv-deprecate.service watches vlan-* for networkd removing a
dynamic address and sends RAs with that /64 at preferred lifetime 0 via
a short-lived radvd (SIGKILLed: no shutdown RA). Identical script to the
upstream commit; drop once the cnx-network input is bumped past it.
Verified on stellio: the stale prefix flipped to deprecated on the
client at the first RA and pings resumed; a synthetic dynamic address
removed from vlan-lan produced the same RA end to end.
kurogeek
31ebf2d081