IPv6 DHCP not updated when prefix changes

[elbertmai]

As @AndrewZ alluded to, firewall rules can still work even in the face of dynamic prefixes.

Fortunately OpenWrt supports this using a negative netmask notation. I've talked about how you can use this in LuCI in a previous post of mine:

IPv6, SLAAC, DHPv6 and Port Forward

Before you do all that, you need to do these things first, assuming that OpenWrt hasn't been modified beyond the port forwards you have: Go to the LuCI home page, scroll down to "Active DHCPv6 Leases", and click "Set Static" on the server host. There should be only one entry for each host but multiple IPv6 address associated with it. Go to "Network" → "DHCP and DNS" in the LuCI menu, then click on the "Static Leases" tab. Click "Edit" on the hostname entry. Assign an "IPv6-Suffix (hex)" to the…

Once this is working then you should not need to worry about changing prefixes.

@SuperMitic

The problem is that when IPv6 prefix changes, the PC is keeping the old one.

This shouldn't be a problem. When a router announces a prefix either through RA or DHCPv6, the router also sends lifetime information about the prefix. The prefix goes through a validity/deprecation lifecycle so existing connections aren't disrupted. Your PC would then just have multiple IPv6 addresses, one for new connections and the rest for existing ones.

If you're using dynamic DNS, have the updater running on the PC send a AAAA record update with the appropriate TTL every time the PC receives a new prefix. The record should only contain the most recent prefix and not any of the deprecated ones.