ipv6 tunnel...

tunneling ipv6 through ipv4...

establish connectivity with an ospf network, as below...

variations on a theme...

r1#sh run int tun 0
Building configuration...

Current configuration : 136 bytes
!
interface Tunnel0
 no ip address
 ipv6 address 2001::1/64
 ipv6 ospf 1 area 0
 tunnel source 1.1.1.1
 tunnel destination 2.2.2.2

r2# sh run int tun 0
Building configuration...

Current configuration : 136 bytes
!
interface Tunnel0
 no ip address
 ipv6 address 2001::2/64
 ipv6 ospf 1 area 0
 tunnel source 2.2.2.2
 tunnel destination 1.1.1.1

it's really that easy after you've built ospf...

r1#sh ipv6 int tun 0
Tunnel0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::C80A:61FF:FEA8:8
  No Virtual link-local address(es):
  Global unicast address(es):
    2001::1, subnet is 2001::/64
  Joined group address(es):
    FF02::1
    FF02::2
    FF02::5
    FF02::1:FF00:1
    FF02::1:FFA8:8
  MTU is 1476 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ICMP unreachables are sent
  ND DAD is enabled, number of DAD attempts: 1
  ND reachable time is 30000 milliseconds (using 30000)
  ND RAs are suppressed (periodic)
  Hosts use stateless autoconfig for addresses.

r2#sh inter tun 0
Tunnel0 is up, line protocol is up
  Hardware is Tunnel
  MTU 17916 bytes, BW 100 Kbit/sec, DLY 50000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source 2.2.2.2, destination 1.1.1.1
  Tunnel protocol/transport GRE/IP
    Key disabled, sequencing disabled
    Checksumming of packets disabled
  Tunnel TTL 255, Fast tunneling enabled
  Tunnel transport MTU 1476 bytes
  Tunnel transmit bandwidth 8000 (kbps)
  Tunnel receive bandwidth 8000 (kbps)
  Last input 00:00:04, output 00:00:06, output hang never
  Last clearing of "show interface" counters 00:14:14
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     98 packets input, 10264 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     109 packets output, 11472 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out