IPv6 prefix delegation not working as expected

[MK2]

good morning people,

I currently have a problem in the lab in connection with IPv6 (oh yes it is still alive) and an MX appliance with upstream Fritzbox.

The problem is the IPv6 prefix delegation, the upstream router (fritzbox) gives a /57 prefix to the MX, which passes a /64 subnet to the clients in the subnets enabled for IPv6. The prefix comes via DHCPv6 to the MX.

My problem is that this prefix expires relatively quickly (about 2h) and then it hangs during the renewal. somehow then no new prefix arrives at the MX, or it gets none and the prefix expires and becomes inactive. the clients get but first not notice this and notice the problem only in that some services and websites no longer work as usual, eg YouTube.

I will attach screenshots later. 

[alemabrahao]

Have you checked this?

https://documentation.meraki.com/?title=MX%2FNetworks_and_Routing%2FIPv6_Support_on_MX_Security_%26_...)

[MK2]

yes I have, unfortunately I'm also not clear from it.
My problem is that the delegated prefix expires, but the MX does not immediately fetch a new one. I then always have about 30 minutes no working IPv6 on the clients.

I'll try it with a fixed delegation.

any idea is welcome.