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I have a dual router setup (two routers behind each other) and I want to get IPv6 working on my Local Network.

ISP <-> Router_1 (Vodafone Station) <-> Router_2 (Unifi USG) <-> Local Network

  • Router_1 gets a global IPv6 address and also gets a Prefix-Delegation from the ISP.
  • Clients directly connected to Router_1 also successfully get global IPv6 addresses.
  • Clients connected to Router_2, however, are not able to get a global IPv6 addresses (only link-local).

What I now want to achieve is that the Router-Advertisement from Router_1 is "forwarded" across the Router_2 into my Local Network.

Why? Because my Router_1 does not support the further Prefix-Delegation to another router. Therefore I need to use the DHCPv6-Server that's on the Router_1.

Reading through documentation on IPv6, DHCPv6, Router Advertisements and SLAAC, I still can't seem to figure out if this is actually supported or not.

Kai Neumann
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This usually just won't work, as it would mean the same prefix is used on both interfaces of router 2 (outer and inner). It's the same thing as trying to use the exact same "192.168.1.0" for both networks.

Sharing a prefix could kind of be done on a Linux router using special proxy-ndp software which also manages routes for individual addresses, instead of whole subnet (I think ndppd had this additional feature).

I don't think there is anything for proxying Router Advertisements – it would usually make more sense to just make the other router generate them on its own, and to serve its own DHCPv6 on a non-conflicting range.

u1686_grawity
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  • Thanks, that makes a lot of sense. Then I think there's no way forward for me, because a) my Router_1 does not support the further Delegation of Prefixes (crappy Home-Router from my ISP) and b) I can't simply instruct my Router_2 to go ahead and distribute some random (specific by me) prefix, because it won't be unique / correct, right? – Kai Neumann Feb 20 '21 at 22:12
  • Actually, wouldn’t it work if I create a static IP on the WAN interface of the Router_2 and make sure that I exclude that static IP from the DHCPv6 pool on my LAN interface? – Kai Neumann Feb 21 '21 at 08:49
  • Not entirely, but maybe. If you took e.g. a /96 and used it for your LAN, then your "outer" router would still think that the entire /64, including the "inner" devices, is on-link (even though the USG separates the two links) and would try to make Neighbour Solicitation queries for it. You would _still_ need the USG to perform Proxy-NDP for the chopped-out /96, though wouldn't need the dynamic route updating now. – u1686_grawity Feb 21 '21 at 19:56