IPv6 automatic 6-to4 tunnel

Hi again

I could not get this working today, in my mock.
The question was vague, but the only possibility I saw was automatic 6-to4
tunnel.
The requirement was to establish IPv6 connectivty between R4 and R6
loopback6 interfaces,
maintaining reachability when network failure, while not installing ipv6 on
any of the router in between.

My config was as follow:
---snip---
R4#sh run | s Tunnel|Loopback1|ipv6 route|unicast
ipv6 unicast-routing
interface Tunnel1
   no ip address
   no ip redirects
   ipv6 address 2002:44:44::4/64
   ipv6 rip TAG enable
   tunnel source Loopback1
   tunnel mode ipv6ip 6to4

interface Loopback1
   ip address 4.4.4.4 255.255.255.255
interface Loopback6
    ipv6 add 2001:4::4/64

ipv6 route 2002::/16 Tunnel1

R6#sh run | s Tunnel|Loopback1|ipv6 route|unicast
ipv6 unicast-routing
interface Tunnel1
   no ip address
   no ip redirects
   ipv6 address 2002:66:66::6/64
   ipv6 rip TAG enable
   tunnel source Loopback1
   tunnel mode ipv6ip 6to4

interface Loopback1
   ip address 6.6.6.6 255.255.255.255

interface Loopback6
   ipv6 add 2001:6::6/64
ipv6 route 2002::/16 Tunnel1
---snip---

I had reachability between R4 and R6 Lo1 interfaces, but could not get
reachability through the tunnels.

Please advise if you can spot something I did wrong,
Thanks

-- 
<ruhann>
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