I have a RB2011UAS-2HnD-IN running RouterOS 6. It's connected to a residential PPPoE internet connection supporting IPv6. Over this connection I get a dynamic /64. In addition to that I use DHCPv6 to get an additional (also dynamic) /48 which is then used to cut /64s out for internal interfaces. Let me emphasize again, that both, the PPPoE /64 and the /48 are dynamic, just like IPv4 addresses usually are on residential internet connections.
My setup and configuration works well except for one little detail:
The prefix that is delegated via DHCPv6 might have a longer lease time than the PPPoE connection persists. Usually there is no relation between the lease time of a DHCP(v6) lease and the interface it was recieved on.
But in this case there is. If the PPPoE connection gets disconnected (there is a forced disconnect after some hours from the ISP) and the router reconnects it recieves a different /64 and a new /48 prefix via DHCPv6. Also the old prefixes cannot be used anymore via the PPPoE connection.
The router appears to relate the /48 prefix to the pppoe interface. When I unplug the DSL modem the prefix disappears from the dhcp-client and the interface gets the status "stopped". The problem is that the prefix (or better a /64 slice out of it) is still on the internal interface which still sends our router advertisements telling everyone and their brother about it with a lifetime of a few hours. When the reconnection is successful and there is the new prefix being put on the interface, the router starts advertising this prefix. The old and unusable prefix remains on the clients until its preferred lifetime is over. And this is the core of the problem: The removed/replaced prefix is not "deprecated" by sending out router advertisements with preferred lifetime "0".
May I point you to RFC6204 Basic Requirements for IPv6 Customer Edge Routers
which clearly states:
If the delegated prefix changes, i.e., the current prefix is
replaced with a new prefix without any overlapping time
period, then the IPv6 CE router MUST immediately advertise the
old prefix with a Preferred Lifetime of zero and a Valid
Lifetime of the lower of the current Valid Lifetime and 2
hours (which must be decremented in real time) in a Router
Advertisement message as described in Section 5.5.3, (e) of
[RFC4862].
