Because you are missing the point of subnetting completely. You should be using: "ip -6 addr add 2001:610:6c9::1/64 dev br0" on the router. Then you can optionally use radvd to announce that /64, or you could manually configure an address on every box on that subnet. You could indeed use eg a /126 or something else silly, but why? You got a /48 for that network. As it is a /48, you can use 2001:610:6c9:0000::/64 (which you are using apparently on eth2), 2001:610:6c9:0001::/64, 2001:610:6c9:0002::/64 upto 2001:610:6c9:ffff::/64, that is 65536 /64's to use for your pleasure. Should be enough I guess... As to why it didn't work what you are trying: - You are using /128's. - You are routing the same subnet to two interfaces. - You might have a broken multicast setup somewhere. (Which would not be suprising as you have a br0 which might just be WRT and some WRT platforms have problems with multicast). Please actually read the FAQ which has a very nice section on how to provide connectivity to other hosts in your subnet. And the Wiki also contains a nice example about Subnetting.