The gateway IPv6 address you are using is wrong, it is a link-local IPv6 address and local to each device and you cannot connect to it. Try to find the IPv6 of your unifi router, mine is fd88::1 for Openwrt router.
I can confirm that this works, on my Openwrt I can see that lease is expired on shutdown (correct way) and kept the DUID the same.
Proxmox staff needs to look into this and remove the line that removes dhclient files.
This behavior is because /usr/share/ifupdown2/sbin/start-networking contains this dirty hack for unknown reasons^
stop)
if [ "$SKIP_DOWN_AT_SYSRESET" = "yes" ]; then
SYSRESET=0
systemctl list-jobs | egrep -q...
Only the line "find /var/lib/dhcp/ -name "dhclient*leases" -delete" needs to be removed.
The problem is, this script is a part of ifupdown2 package and any change would be lost during upgrade.
On my home server I commented "SKIP_DOWN_AT_SYSRESET...
I checked and it is not configured for my VMs and they all have native IPv6 connectivity.
This is what I have in the config
[OPTIONS]
enable: 1
radv: 1
macfilter: 1
policy_in: ACCEPT
[RULES]
|GROUP deny-lan-access
I also have firewall enabled on the datacenter level and IPv6 is working fine for both Proxmox and VMs.
Are you also allowing router advertisements?
accept_ra 2
Example