I have my ISP's router connected  to the Broadband line, and that works as expected.

My 2685 is then configured to use WAN2 ethernet connected and sits behind the ISP's router.

This works just file for IPV4 but I cannot seem to get IPV6 to work.

WAN2 gets an IPV6 address but the DHCP server in the 2685 does not issue an IPV6 address that can be touted to the internet.

Any help / pointers appreciated

Apologies, I don't have time to write a full answer / explanation here, but I do recommend doing some reading on how IPv6 addresses are assigned to LAN clients, this may help you diagnose the problem.

In short, DHCP in the standard sense is often NOT what is used to assign IPv6 addresses. It can be used in some cases, in the form of DHCPv6, but often, SLAAC (Stateless Auto-configuration) is used, whereby the client basically assigns itself an address.

Might point you in the right direction? I don't currently have IPv6 running on my network as my ISP does not provide it, although I have used it on a 2865 in the past.

Thanks for your reply, I had been doing some more reading even after I posted my original question. I eventually found a page that explained things a little differently and I tried what it suggested. Turning on bridge mode for IPV6 seems to have done the trick and its now working as I would expect.

That said Whilst I have read the words on the firewall part of that configuration page, I am not 100% sure if I should click that checkbox or not. Do you have any thoughts or pointers on that?

Could you elaborate slightly as to what 'Bridge Mode' you have turned on? Which menu is this in?

Do you mean the 'Block routing connections initiated from WAN' checkbox?
 

The option I turned on was in:

WAN>Internet Access>IPV6 (on the right of the WAN2 line)

which is set up as a "Static or Dynamic IP."

On that page at the bottom left you have bridge mode, I have both boxes ticked. That gets my PC an IPV6 address.

Now my issue is getting IPV6 to work on WAN1 - which I have yet to work out. Everything I have tried so far fails to assign an IPV6 address to the PC.

I see - I hadn't noticed that bridge mode option before. I don't recall ever using it...

I suppose you have no reason to complain if it is working, but I would be very careful to check the 'Enable Firewall' box, and use some external tools to make sure your PC is not exposed on the internet via its IPv6 address. 

Do you have any details about the IPv6 address space provided by your ISP? What size prefix do they delegate to customers?

As to WAN1, do you have WAN2 IPv6 online at the same time as trying to setup WAN1 with IPv6? I am not sure if the Draytek will give your PC an IP from BOTH WAN interface's IPv6 ranges at the same time. I would have thought it would be one or the other.