Teredo is enabled by default on Windows Vista/7 (like IPv6) but is inactive until required.
1. Check status
You can verify if you are using the Teredo feature (in relation with IPv6).
You can use cmd prompt, and type the following commands:
And see if you have an IPV6 address that starts with “2001:”
You can use netsh (open a cmd prompt) and type the following commands:
netsh interface teredo show state
netsh int ipv6 show teredo
Should be ‘offline’, if not ( like state is ‘dormant’) that means your tunnel is possible.
Nota : this action requires “Administrators” privileges
netsh interface teredo set state disabled
To set it back to default again use:
netsh interface teredo set state default
Some old but detailed information: http://www.mydigitallife.info/2007/09/09/how-to-disable-tcpipv6-teredo-tunneling-in-vista/