As a user of both TomatoUSB and DD-WRT, I'm familiar enough with the changes necessary to get IPv6 working on both DD-WRT and TomatoUSB.
So! I will be providing an IPv6 6in4 set-up, again with Hurricane Electric as our IPv6 provider here at Heimkoma Services with DD-WRT.
At some point between the original revision (revision unknown) where DD-WRT on my TP-Link WDR-4300 mentioned in Setting up a VAP on DD-WRT, the interface and managing IPv6 had been changed.
Previously, to get IPv6 working, I had to go the convoluted way of getting IPv6 going on DD-WRT using a script that was posted on the DD-WRT Wiki... but now there's an entire tab dedicated to IPv6 under Setup > IPv6.
This screen was different enough from TomatoUSB that it threw me off, which required a confirmation of my set-up over on Hurricane Electric's Forum.
With a working set-up now, I can now tell you to forget all about DD-WRT's convoluted script. The IPv6 screen works perfectly for our purposes.
Here's a screenshot below so you have an idea of how to make this work.
As mentioned in my previous article, relevant details have been blacked out. Notice the IPv6 help section to the right? Unhelpful, right? So, let's get you up and running!
Getting the Router Address
To get the Router IPv6 IP, this is your routed /64. ie, Routed IPv6 Prefixes in Hurricane Electric's tunnelbroker page. Do not use the /64. Just the full routed /64 as listed. So for example, if your routed prefix is 2001:xxx:xx:xxx::/64, input 2001:xxx:xx:xxx:: as your Router IPv6 Address.
Getting the MTU
The MTU as listed on my screenshot here is easily found under the Advanced page for your tunnel details page.
Everything else, you can get on your tunnelbroker tunnel details page. Simply match the tunnel details to the screen in the screenshot provided above and Bob's your uncle!