version 12.4
ipv6 unicast-routing
ipv6 cef
!
interface Tunnel0
 no ip address
 no ip redirects
 ipv6 address 2001:1:2:3::/64 eui-64
 no ipv6 nd suppress-ra
 tunnel source Ethernet0/0
 tunnel mode ipv6ip isatap
!
interface Ethernet0/0
 ip address 192.168.1.1 255.255.255.0
 half-duplex
!
interface Ethernet0/1
 no ip address
 half-duplex
 ipv6 address 2001:A:B:C::1/64
!
ip forward-protocol nd
!

Version 12.4(25)

Router#show ipv int
Ethernet0/1 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::CE00:EFF:FE74:1
  Global unicast address(es):
    2001:A:B:C::1, subnet is 2001:A:B:C::/64
  Joined group address(es):
    FF02::1
    FF02::2
    FF02::1:FF00:1
    FF02::1:FF74:1
  MTU is 1500 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ND DAD is enabled, number of DAD attempts: 1
  ND reachable time is 30000 milliseconds
  ND advertised reachable time is 0 milliseconds
  ND advertised retransmit interval is 0 milliseconds
  ND router advertisements are sent every 200 seconds
  ND router advertisements live for 1800 seconds
  Hosts use stateless autoconfig for addresses.
Tunnel0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::5EFE:C0A8:101
  Global unicast address(es):
    2001:1:2:3:0:5EFE:C0A8:101, subnet is 2001:1:2:3::/64 [EUI]
  Joined group address(es):
    FF02::1
    FF02::2
    FF02::1:FFA8:101
  MTU is 1480 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ND DAD is not supported
  ND reachable time is 30000 milliseconds
  ND advertised reachable time is 0 milliseconds
  ND advertised retransmit interval is 0 milliseconds
  ND router advertisements live for 1800 seconds
  Hosts use stateless autoconfig for addresses.