The problem is essentially everywhere. Router/OS programmers are programmers too, and some are more on the ball than others.
In the consumer router space, the level and quality of IPv6 support is far from perfect. Even the third-party firmware is spotty. IPv6 works fairly well on OpenWRT trunk, thanks to 6relayd and odhcp6c, but the best you'll get from DD-WRT is a kernel module and a pile of scripts in the wiki.
In the consumer router space, the level and quality of IPv6 support is far from perfect. Even the third-party firmware is spotty. IPv6 works fairly well on OpenWRT trunk, thanks to 6relayd and odhcp6c, but the best you'll get from DD-WRT is a kernel module and a pile of scripts in the wiki.