The u6rd is a user-space 6rd (RFC 5569) implementation, which uses
tun(4) and the raw socket interface.
The u6rd daemon runs on the 6rd border router of a 6rd site that is
isolated from the native IPv6 Internet. It does not provide the
functionality of 6rd "relay" routers.

WWW: http://www.scythe.jp/lab/u6rd/