Packet loss over GRE tunnels

I am messing about with GNS3, and what i've done is built a topology with four routers running IPv6 with OSPFv3, two routers are connected to all.

On one of the routers connected to two of the IPv6 routers, i've connected another router running IPv4 with OSPF, and the other IPv6 router with 2 connections, i've connected another router running IPv4 with OSPF. It effectively looks like a diamond.

I've then built two tunnels on these routers, one on each of the interfaces, and used an IPv4 address as the IP address on the tunnel. OSPF formed adjacencies between the two tunnel interfaces, and the routers just running IPv4 and OSPF can successfuly ping eachother. However, every fourth packet is dropped.

I guess some of you may turn around to me and ask "what on earth are you doing", but honestly, i'm just playing around and seeing if I could achieve what I created in my mind. What I would like to know, is what is causing every fourth packet to be dropped? Where should my efforts focus?

I have pasted one of the tunnel interfaces configs below, along with a show interface of the same tunnel:

interface Tunnel1 ip address 172.20.10.10 255.255.255.252 tunnel source Ethernet0/2 tunnel mode ipv6 tunnel destination 2001:AA00:FB01:3DA1:A8BB:CCFF:FE00:C00 end Tunnel1 is up, line protocol is up Hardware is Tunnel Internet address is 172.20.10.10/30 MTU 1460 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 linestate evaluation up Tunnel source 2001:EEEE:1A5D:CE56:A8BB:CCFF:FE00:1020 (Ethernet0/2), destination 2001:AA00:FB01:3DA1:A8BB:CCFF:FE00:C00 Tunnel Subblocks: src-track: Tunnel1 source tracking subblock associated with Ethernet0/2 Set of tunnels with source Ethernet0/2, 1 member (includes iterators), on interface <OK> Tunnel protocol/transport IPv6 Tunnel TTL 255 Tunnel transport MTU 1460 bytes Tunnel transmit bandwidth 8000 (kbps) Tunnel receive bandwidth 8000 (kbps) Last input 00:00:00, output 00:00:04, output hang never Last clearing of "show interface" counters 00:41:07 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 1382 packets input, 184164 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 326 packets output, 40748 bytes, 0 underruns 0 output errors, 0 collisions, 0 interface resets 0 unknown protocol drops 0 output buffer failures, 0 output buffers swapped out 

If I do a ping from the router with the tunnel to a router beyond the tunnel, no packets are dropped. If I do a ping from a router beyond the tunnel to a router beyond the tunnel, I get packet loss on what appears to be Tunnel1 above:

R8#traceroute 172.20.10.1 Type escape sequence to abort. Tracing the route to 172.20.10.1 VRF info: (vrf in name/id, vrf out name/id) 1 10.50.1.1 5 msec 4 msec 5 msec 2 10.30.1.1 9 msec 10 msec 9 msec 3 10.10.1.18 10 msec 9 msec 10 msec 4 * 172.20.10.10 10 msec * 5 172.20.10.1 16 msec 15 msec 15 msec 

What's really confusing is the Tunnel says there are no drops or any other errors.