DD-WRT with native IPv6

Sounds like you have got the connectivity part working, but you're actually not acting as a router.

You must find out the following from your ISP:

• Whether the subnet assigned to your ppp0 interface is the same one you use for your LAN
• How the subnet is delegated to you (static, DHCPv6, etc.)

These WRT54G builds include DHCPv6-PD support, which works with Internode, an Australian ISP, but you have said you are from Norway, and your ISP does not necessarily do it the same way.

You have mentioned radvd, but that is pretty much irrelevant — you need to figure out what the subnets are before you go anywhere near something like radvd. sysctl net.ipv6.conf.all.forwarding=1 is a good start, but you still need more.

If you go to the ADSL FAQ from Internode, they provide this information:

The IPv6 Broadband Trial allows Internode customers to test and gain experience with IPv6 using their existing Internode ADSL service.

What will this give me?

• Your existing IPv4 address (if static) and route(s)
• A dual-stack IPv4/IPv6
• A dynamic /64 IPv6 prefix for your PPP session
• A stable /60 IPv6 prefix for your LAN (if you are using a router with Prefix Delegation)

How do hosts on my LAN obtain globally routed IPv6 addresses?

Your IPv6 Access Device/router should assign /64 subnets to it's interfaces after it obtains a DHCPv6 PD lease. It should then offer the prefix to your hosts via IPv6 Stateless Address Autoconfiguration. In more complicated setups you may choose to use DHCPv6 as well.

You must find out the equivalent information from your ISP. I'd hazard a guess that you need something like a DHCPv6-PD–enabled setup, but we can't know for sure until we get more information. Heck, we don't even know what your ISP is.

If you only have one /64 prefix and that prefix is on your WAN side then you can't do IPv6 for your LAN. An ISP is supposed to give you multiple /64s so that you can put a separate /64 on each LAN. It is common for an ISP to give everybody (residential and business) a /48 (65536 /64s). For residential customers they might hand out a /56 (256 /64s). That way you have plenty prefixes to number your network, even if it gets more complicated over time (Internet-of-Things deployment etc).

Some ISPs are still sticking too much to the IPv4 mentality and only giving out a /60 (16 /64s) or so. While that will probably be enough now it will cause problems as IP-capable devices become more common, and you don't really want your living room lighting and AC to be in the same subnet as the children's toys, do you? ;)

ISPs that only hand out a single /64 prevent you from any subnetting at all. If that /64 is on the WAN interface then you'll never get decent IPv6 on your LAN(s). This is the ISPs fault and they should fix this by giving out a decent amount (/48 or /56) of addresses.