>>53
up/upになってます。

>>55
勉強用なので、IPは特にマスクせず不要なところを削除してアップします。

R4#show ipv6 interface vlan 100
Vlan100 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::20F:24FF:FE85:3CF6
Global unicast address(es):
A::2, subnet is A::/16


R4#show ipv6 interface
FastEthernet0 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::20F:24FF:FE85:3CF6
Global unicast address(es):
C::1, subnet is C::/16

Vlan100 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::20F:24FF:FE85:3CF6
Global unicast address(es):
A::2, subnet is A::/16