Windows Vista and Windows 7 both come equipped with dual stack IPv4/IPv6, and it can be enabled on Windows XP/SP2. On a default installation of Vista/Win7, IPv6 should already be operational. In order to fully test your IPv6 readiness, you will also need the services of a Tunnel Broker. A Tunnel Broker is a server that sits on both an IPv6 network and an IPv4 network. IPv6 packets are encapsulated inside an IPv4 packet and sent out over the IPv4 network. The server strips the IPv4 info and sends the packet on to the IPv6 server. Return packets follow the reverse route.

Vista/Win7 come equipped with the Teredo Tunnel, but it is not functional by default. To get all these working, the following services must be running:
IP Helper – Automatic Started
Windows Firewall – Automatic Started
Base Filtering Engine – Manual Started
Don’t ask me why the Firewall has to run, but Microsoft says that the Teredo Tunnel is a security risk. To the best of my knowledge, the Teredo Tunnel is the only one that will work behind a NAT router that does not support IPv6. It uses a technique similar to PPP networks, with a specific UDP port being used to maintain contact.

One of the major differences with IPv6 is that there can be multiple IP addresses. Since there is no longer a Netmask to determine if an address is on the local network, or if it has to be routed through a gateway, they have introduced something call a link-local address. If you go to the command prompt and enter the “ipconfig /all” command, you should see an address beginning with “fe80::” and ending with “%x” under the Local Area Connection. The “%x” is a random ID number assigned to the interface, and will be necessary to use at times (more on that later).

If the system only has a link-local and a Teredo tunnel IP address, the DNS will not return an IPv6 address. To overcome this limitation, we have to fool the system by adding another IPv6 address. If you are fortunate enough to have a router that supports IPv6 DHCP, one will already have been assigned to you. If not, you must manually enter it. Go to the Properties of your LAN or WiFi interface, and change it to have a static IPv6 address. The easiest solution is to use the converted IPv4 address with a netmask of 48. For example, a static IPv4 address of “192.168.1.2” converts to “2002:c0a8:102::” (192 = c0h, 168 = a8h, 1 = 01h, 2 = 02h). Don’t configure a default gateway for this address, because there isn’t one.

On one machine I had difficulty getting the ping command to use the correct interface. It wanted to use the Teredo link-local address instead of the ethernet adapter link-local address. I solved the problem by disabling the other Microsoft interface via the registry. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\DisabledComponents
This key probably won’t exist and must be added as a REG_DWORD. The value is a bit map:
· Bit 0 Set to 1 to disable all IPv6 tunnel interfaces, including ISATAP, 6to4, and Teredo tunnels.
· Bit 1 Set to 1 to disable all 6to4-based interfaces.
· Bit 2 Set to 1 to disable all ISATAP-based interfaces.
· Bit 3 Set to 1 to disable all Teredo-based interfaces.
· Bit 4 Set to 1 to disable IPv6 over all non-tunnel interfaces, including LAN interfaces and *Point-to-Point Protocol (PPP)-based interfaces.
· Bit 5 Set to 1 to modify the default prefix policy table to prefer IPv4 to IPv6 when attempting connections.
To disable the ISATAP interface, I changed the value to 4 (bit 2).

At this point, we need to expose you to a command that has always been there, but wasn’t really used much with IPv4.
C:\>netsh int ipv6 show teredo
Teredo Parameters
---------------------------------------------
Type : client
Server Name : teredo.ipv6.microsoft.com.
Client Refresh Interval : 30 seconds
Client Port : unspecified
State : dormant
Client Type : teredo host-specific relay
Network : managed
NAT : none (global connectivity)
“Int” is short for “interface”. If the state shows as “offline”, you may have to force Teredo into accepting your NAT router. This is done using the following command:
C:\>netsh int ipv6 set teredo type=enterpriseclient
Ok.

If Teredo is now functional, then you should be able to find the interface index using the “ipconfig /all” command:
Tunnel adapter Local Area Connection* 6:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
Physical Address. . . . . . . . . : 02-00-54-55-4E-01
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
IPv6 Address. . . . . . . . . . . : 2001:0:4137:9e76:142b:a209:30f9:a279(Preferred)
Link-local IPv6 Address . . . . . : fe80::142b:a209:30f9:a279%8(Preferred)
Default Gateway . . . . . . . . . : ::
NetBIOS over Tcpip. . . . . . . . : Disabled
In the example above, the interface index is %8 for the Teredo interface. We need this number for the next command, since there is no default route to allow traffic to flow to the Internet.
C:\>netsh int ipv6 add route ::/0 interface=8
Ok.

With this last step you should now be able to access IPv6 sites such as:
C:\>ping ipv6.google.com
Pinging ipv6.l.google.com [2001:4860:b006::69] from 2001:0:4137:9e76:249b:92d7:b464:60e9 with 32 bytes of data:
Reply from 2001:4860:b006::69: time=31ms
Reply from 2001:4860:b006::69: time=31ms
Reply from 2001:4860:b006::69: time=31ms
Reply from 2001:4860:b006::69: time=31ms
Ping statistics for 2001:4860:b006::69:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 31ms, Maximum = 31ms, Average = 31ms
It may take more than one attempt to activate the interface. Then try entering http://ipv6.google.com into your browser, and it should bring up Google’s IPv6 page.

Be aware that at this point in time, Windows will always prefer IPv4 over IPv6 if both exist for a given domain. We can change that behaviour by modifying the prefixpolicies table:
C:\>netsh int ipv6 show pre
Querying active state...
Precedence Label Prefix
---------- ----- --------------------------------
50 0 ::1/128
40 1 ::/0
30 2 2002::/16
20 3 ::/96
10 4 ::ffff:0:0/96
5 5 2001::/32
But I will leave that for you to investigate on your own.

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