We have performed double NATing with 2 routers because of some security requirements (Diagram can be found in the attached).

Just recently, we needed to set up ipv6 for the entire office but experienced connectivity issue;
We used he.net to create a tunnel and did the following configuration.
PC was not able to ping the end point of IPV6 tunnel.

On 450G:
/interface 6to4 add comment="Hurricane Electric IPv6 Tunnel Broker" disabled=no local-address=115.66.1.1 mtu=1280 name=sit1 remote-address=216.218.221.42
/ipv6 route add comment="" disabled=no distance=1 dst-address=::/0 gateway=2001:470:35:493::1 scope=30 target-scope=10
/ipv6 address add address=2001:470:35:493::2/64 advertise=yes disabled=no eui-64=no interface=sit1
/ipv6 address add address=2001:470:36:493::2/64 advertise=yes disabled=no eui-64=no interface=ether4-local

On 495G:
/ipv6 address add address=2001:470:36:493::1/64 advertise=yes disabled=no eui-64=no interface=ether2-dmz
/ipv6 route add comment="" disabled=no distance=1 dst-address=::/0 gateway=2001:470:36:493::2 scope=30 target-scope=10
/ipv6 address add address=2001:470:37:493::2/64 advertise=yes disabled=no eui-64=no interface=bridge-interface

From PC, I was able to ping:
2001:470:37:493::2
2001:470:36:493::1
but not any other IP addresses

From 493G, I was able to ping:
2001:470:36:493::2
2001:470:35:493::2
2001:470:35:493::1

The 450G was able to ping:
2001:470:35:493::2
2001:470:35:493::1

Any idea why I cannot ping 2001:470:35:493::1 from the PC

Did your computer receive ipv6 adresser other than link-local address? I could be that those addresses played you a trick.
What about gw on the computer?

This was what I did. On Windows :

Ohh.. to me it seems that your windows have a ::/0 (default route to a fe80..... address, this is a link local address.

http://en.wikipedia.org/wiki/IPv6_addre ... ne_indices

Add a correct default gw and try again.

Hmm..looks like the outcome is still the same..
Attached is the a screen shot of the new default gateway. I have manually added it.