I have a Buffalo WHR-HP-G54S, and have been using Shibby's MiniIPV6 firmwares because they are one of the few firmwares around which enable IPV6 functionality in older, MIPSR1, 4MB flash routers. Thank you Shibby.
Thanks to another user's tutorial (./t-473266/howto-ipv6-using-6rd), I've been successfully running a 6rd setup since Shibby 093.
This 6rd setup is now broken as of 099. Last working was 097. I believe this is because, starting in 099, a bunch of modules, specifically tunnel4.ko, were moved into the "extras" package as part of the IPsec patch.
The 6rd script requires both tunnel4 and sit to be available to insmod, and if one tries to insmod sit before tunnel4 on 097 and below, one will notice that sit spits out an undefined symbol error and refuses to insert. (see also: ./t-279512/sit-kernel-module-problem-already-fixed) Therefore sit.ko itself depends on tunnel4.ko. Further confirmed if one greps the modules.dep file in 097 or below, which will show they are linked as deps. Naturally, without tunnel4 available, sit cannot be inserted at all on 099 and 100.
So the options would appear to be: (1) move tunnel4.ko back into the base firmware, (2) move sit.ko to extras as well, since it needs tunnel4.ko. My vote, at the very least for conveinence, would be (1), especially as this essentially broke previous functionality.
Supposedly 6rd using DHCP Option 212 has been added in 100, but it is also not working for me. No idea if that is my ISP not supporting Option 212, or is further related to the absence of tunnel4.ko.