>>544
ip route 0.0.0.0 0.0.0.0 Dialer1
ipv6 unicast-routing
ipv6 route ::/0 Tunnel0

interface Tunnel0
description For_IPv6_connection
no ip address
ipv6 address 2001:380:xxxx::1/64
tunnel source Dialer1
tunnel destination 61.207.xxx.xxx
tunnel mode ipv6ip
tunnel path-mtu-discovery

interface FastEthernet0/1
ip address 192.168.0.1 255.255.255.0
ip nat inside
ip virtual-reassembly
ip tcp adjust-mss 1414
ipv6 enable
ipv6 address xxxx:xxxx:xxxx:xxxx::x/64
ipv6 nd prefix xxxx:xxxx:xxxx:xxxx::/64

適当に書いてみたが環境が無いので動くかどうかは知らん。