IPv6 GRE tunnel not working.

Hi Experts,

I am trying to create a IPv6 tunneling interface between 2 routers.

R1#sh run int tu 12
Building configuration...

Current configuration : 136 bytes
!
interface Tunnel12
 no ip address
 ipv6 address 2001:12::1/64
 ipv6 enable
 tunnel source Loopback0
 tunnel destination 10.0.0.2
end

R2#sh run int tu12
Building configuration...

Current configuration : 136 bytes
!
interface Tunnel12
 no ip address
 ipv6 address 2001:12::2/64
 ipv6 enable
 tunnel source Loopback1
 tunnel destination 10.0.0.1
end

The tunnel is up.

R1#sh int tu 12 | i up
Tunnel12 is up, line protocol is up
R2#sh int tu 12 | i up
Tunnel12 is up, line protocol is up

The IP4 connectivity between these 2 interfaces are fine. But I'm not able to ping the IPv6 address of the tunnel.

R2#p 2001:12::1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:12::1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

R1#p 2001:12::2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:12::2, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)


Can you guys please help me with this?

Krishna