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Chaining routers and GUA IPv6 addresses (lemmy.ml)

submitted 1 day ago by [email protected] to c/[email protected]

7 comments fedilink hide all child comments

Hey fellow self-hosting lemmoids

Disclaimer: not at all a network specialist

I'm currently setting up a new home server in a network where I'm given GUA IPv6 addresses in a 64 bit subnet (which means, if I understand correctly, that I can set up many devices in my network that are accessible via a fixed IP to the oustide world). Everything works so far, my services are reachable.

Now my problem is, that I need to use the router provided by my ISP, and it's - big surprise here - crap. The biggest concern for me is that I don't have fine-grained control over firewall rules. I can only open ports in groups (e.g. "Web", "All other ports") and I can only do this network-wide and not for specific IPs.

I'm thinking about getting a second router with a better IPv6 firewall and only use the ISP router as a "modem". Now I'm not sure how things would play out regarding my GUA addresses. Could a potential second router also assign addresses to devices in that globally routable space directly? Or would I need some sort of NAT? I've seen some modern routers with the capability of "pass-through" IPv6 address allocation, but I'm unsure if the firewall of the router would still work in such a configuration.

In IPv4 I used to have a similar setup, where router 1 would just forward all packets for some ports to router 2, which then would decide which device should receive them.

Has any of you experience with a similar setup? And if so, could you even recommend a router?

Many thanks!

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[–] [email protected] 2 points 16 hours ago* (last edited 16 hours ago)

Yeah openwrt should be great. It uses nftables as a firewall on a Linux distribution. You can configure it through a pretty nice ui, but you also have ssh access to configure everything directly if you want.

The challenge is going to be what the ISP router supports. If it supports bridge mode then things are easy. You just put your router downstream of it and pretend like it's a modem. Then you configure openwrt like it's the only router in the network. This is the opposite of what you've suggested, using the upstream ISP router in pass through and relying on the openwrt router to get the ipv6 GUA prefix. (You might even be able to get a larger prefix delegated if you set the settings to ask for it)

If you don't have bridge mode then things are harder. There's some helpful information here https://forum.openwrt.org/t/ipv6-only-slaac-dumb-aps/192059/19 even though the situation is slightly different since they also don't want a firewall. But you probably need to configure your upstream side on the openwrt router similarly.

Also looking more, the tplink ax55 isn't supported by openwrt. If you don't already have it, I'd get something that does. (Or if the default software on the ax55 supports what you want, that's fine too. I just like having the full control openwrt and similar gives)