I recently upgraded from fttc to fttp and have two lines in. Yup greedy I know. I was going to keep the fttc as a back up line but going to fttp was actually cheaper.
Under fttc ipv6 on one connection never worked so i guessed it never got switched on. I tried direct connection and no ipv6.
Fttp ipv6 works but the draytek will only allow you to enable it on one wan input. Deliberate or an oversight?

I've asked on these forums and the network bods at work what happens when you got two ipv6 address's from two different isp's how would that work and never got an answer.
At least on the draytek 3910 you can't turn that on.

Now as sites move over to ipv6 this could be a problem so if your main line goes down and you fail over to another provider you won't be able to access the ipv6 without going into the configuration and enabling.

Do other models allow ipv6 on two different wans?

A poor response from draytek tech support who couldn't be bothered to check too see if it was possible to have two ipv6 lines on 3910.

Basically they don't know if it's possible or now.

Anyone else out there running to lines on a different draytek model out of interest.

A better response from Draytek today.

The guy has now asked their engineers and couldn't get an straight answer.

I'm not surprised by this majority of people don't seem to know how ipv6 works.

The most honest answer is that it's too clever for it's own good.

The question I never got an answer too is what happens when you got two or more internet connections from different providers who both provide ipv6. How does the router sort that out since NAT isn't used or shouldn't be used.