They support probably the most useful dyn dns IPv6 feature: IPv6 for LAN. Duiadns is also supported on Apple Airport routers.
I'm using duiadns service on my old wrt610n router with dd-wrt firmware. The newest versions of dd-wrt have native support for duiadns in DDNS tab settings (Duiadns on dd-wrt). It also supports Apple Airport DDNS.
[Edited by ionutcristian, August 27]
offers support for apple airport routers!
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