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derdeagle
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Posts: 24
Joined: Sat Jun 30, 2018 6:58 pm

Specifying DNS IPv6 address(es) with non-static IPv6 prefix

Sat May 08, 2021 10:04 pm

Hi all,

I am sometimes experiencing my router using a different DNS server as expected.
To give you (hopefully) all necessary details please see below.
network-diagram.png
Uplink
My upling is DSlite.

FritzBox
The FritzBox is a FRITZ!Box 7490 provided by my ISP. It handles the authentication and NATting towards the internet.

gate1
I have the gate1 and gate2 redundantly connected via VRRP. This is just to keep in as complete as possible / necessary, but HA does not work as expected atm. gate1 and gate2 are doing another NAT which means that my FritzBox does not know anything about what is behind gate1 and gate2. I unfortunately had to choose this option because I have several subnets and in the past I couldn't tell the FritzBox the necessary routes (works by now but not yet changed).

gate2
My gate2 is really just idling and not capable of handling all the traffic if gate1 is failing.

sw1
At my switch all me devices are connected which are a few more than in the graph but they are not really necessary.

ns1
ns1 is the primary recursive nameserver (running bind9) which provides internal DNS functionality for me. I have a subdomain only resolved at home so the public DNS servers don't know about the internal names etc.

ns2
ns2 is the secondary recursive nameserver (also running bind9) - just like ns1.

workstation
A client having both IPv4 and IPv6 addresses assigned.

Problem description
Because of DSlite I am not assigned a real IPv4 address but the connection is in a carrier grade NAT. Only the IPv6 connections reaches my FritzBox.
I am assigned a /56 IPv6 prefix by my ISP which the gate1 takes as a client. I then have a /62-pool which hands out /64-prefixes to the devices.
Both my IPv4 and IPv6 addresses are not static which leads to a change like every reboot of the FritzBox or if a timer elapsed (e.g. 1 day).
I am only really using IPv4 internally but wanted to add IPv6.
I have entered my IPv4 addresses of ns1 and ns2 but from the DHCP6 client on my gate1 it receives an IPv6 DNS server. This one of course does not know anything about my internal names etc. which sometimes leads to the situation that I cannot use my address lists because the resolving does not work properly.
When I set the option on gate1 to not receive the IPv6 DNS server DNS stopped working if the clients wanted to use IPv6.

My idea to solve this was to add some ULA pools (unique local address) but I can of course only assign one DHCP6 server on one interface and with this I would need two.

Maybe I am just having trouble to really understand the root-cause of my problem or I am lacking the knowledge to solve it. This is why I am writing here - does anybody have a solution for this (maybe kind of weird) problem?

Thank you in advance!
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