Ethernet shield and IPv6 support Have you heard about support for IPv6 protocol for any Ethernet shield?
As far as I know only IPv4 is supported.
Maybe some one would like to write library?
There is no library, and there physically cannot be one. IPv4 is built into the Ethernet shield itself. (It has a Wiznet 510 chip.)


  Shields based on the MicroChip ENC28J60 chip (such as those sold by Ekitszone and Nuelectronics) are suitable for the implementation of an IPv6 or dual IPv4/IPv6 stack. This approach requires the TCP state machine to be implemented in software and results in more complex arduino code.


Source: this tutorial. (You may find it useful, I'd recommenced reading it.)

There is this library for IPv6 on other hardware, not for the official Ethernet shield.