ipv6 configuration using /48 pool from ISP

RouterOS General
1

This time I have a problem with my ipv6 configuration. My ISP assigned me /48 static network.
I enabled DHCP client, set pool prefix length to 48 - my router received /48 network, eg: 2001:0db8:85a3::/48.

On my router I have two separate bridges, on IPv4 network they are running separate DHCP servers, on IPv6 I want them to use separate /64 prefix.


I opened the addresses tab, assigned address to bridge1, eg: 2001:0db8:85a3:ffff::/64 and set advertise to true.
At this point, all the hosts connected to bridge1 got IPv6 addresses (EUI64: 2001:0db8:85a3:ffff: + mac) and communication was working for them.

What I want to do next is to assign another address to bridge2, eg: 2001:0db8:85a3:aaaa::/64 and have hosts behind it to use that prefix.
When I try to do that, the address is marked as invalid.

I tried to change the prefix length in DHCP client (ISP still assigns me /48 network, but Pool Prefix Length is set to 64), then I can assign addresses to both bridges, but the last part is automatically changed (everytime I click save, eg.: 2001:0db8:85a3:1::/64 then 2001:0db8:85a3:2::/64 etc).

What am I doing wrong?

2

After experimenting for few more hours I think I understand the problem.
When assigning IPs to local interfaces I can use the “difference” between prefix received from ISP and what is set as a pool prefix length.
If I set pool prefix length in dhcp client to 52, I can assign following addresses to the bridges:

2001:0db8:85a3:0000::/64
2001:0db8:85a3:1000::/64
2001:0db8:85a3:2000::/64
...
2001:0db8:85a3:f000::/64

Unfortunately they are not statically assigned (as I wrote earlier each time I press OK the address is increased and after the router restart they first and second one are used).

Is it a limitation of mikrotik IPv6 implementation? In my opinion I should be able to use any of 2001:0db8:85a3:XXXX::/64 as a bridge address.

With such configuration I can use ipv6 as a client, but cannot configure a server, as ip is likely to change after router reboot.