When are IPv6 leases renewed in relation to preferred-life and max-life

[Magnus Holmgren]

Hello, quick question:

My ISP hands out IPv6 leases with a max-life of 86400 (24h) but a preferred-
life of only 7200 (2h), and dhclient -6 (4.4.1-2; Debian 10) only renews the 
lease after half the max-life. This results in the address being deprecated 
most of the time, which causes problems when the kernel chooses an address 
from a VPN as the source for packages to the VPN endpoint, for example.

Is my ISP misbehaving by setting a valid-life less than half the max-life (and 
not specifying renew and rebind times), or is this a bug in dhclient, or 
(least probably) does dhclient try to renew the lease, but the server ignores 
it and dhclient doesn't say anything about this? (Surely having to deprecate 
the only global-scope address on an interface is undesirable?)

Can I supersede override these values in dhclient.conf? Seems you can only 
supersede options, and these are not options?

Thanks,
-- 
Magnus Holmgren        holmgren at lysator.liu.se
                       (No Cc of list mail needed, thanks)