I am running Windows 7 Ultimate, and when I do ipconfig /all in the command prompt I get, in addition to the Ethernet adapter Local Area Connection that I expected, something called Tunnel adapter Teredo Tunneling Pseudo-Interface. What is this? What can I use it for?
Teredo is a protocol that allows computers behind a NAT firewall (most home computers are) and without a native IPv6 connection to access remote IPv6 resources using only UDP protocol. The idea is that home users can start accessing IPv6 web services before their local connection supports the protocol, making the transition from IPv4 easier.
Found this after a quick google.
According to wikipedia, http://en.wikipedia.org/wiki/IPv6, it's some sort of a new TCP/IP protocol .
To make a long story short, it means you have IPv6 installed as part of your networking components. Check the following;
Go to Control Panel and double click Network Connections. Right click on the icon for your Local Area Connection and select Properties from the menu.
On the General page of the properties sheet there's a box which should contain an entry for Microsoft TCP/IP version 6.
I won't bore you with the details but the bottom line is that most people have no need at this time for IPv6. That said, it won't lead to problems if you leave it installed on your computer. That said, uninstalling IPv6 won't cause you to lose your internet connection. The entry you see for Internet Protocol (TCP/IP) is the important one.
If you're curious about IPv6, here's a web site with more information.
IPv6 for Microsoft Windows: Frequently Asked Questions http://www.microsoft.com/technet/network/ipv6/ipv6faq.mspx
If you'd like to disable this in Windows 7:
- Make sure you are an administrator or have access to an administrator account.
- Right click on Computer, choose "Manage."
- In the left-hand menu, under System Tools, left-click on "Device Manager."
- Now, right-click on "Device Manager."
- Hover over "View >" and click "Show Hidden Devices" in the menu that pops up.
- In the center pane, look for a group called "Network Adapters" and expand it by double-clicking on it.
- You will see a list of all of your adapters, including the one in disabled.
I haven't had any issues after disabling these yet. If I become concerned about accessing resources on an IPv6 network, I will re-enable these.
Teredo clients essentially wrap an IPv6 packet in an IPv4 UDP packet and forward it on to a Teredo server.
- The Teredo server is running a publicly accessible IPv4 address.
- The server forwards the IPv4 encapsulated IPv6 packet to its intended destination.
- The Teredo client uses "keep alive" traffic with the server.
- This maintains the NAT mapping between the client's source port and the public IP address (the "client's" or router's public IP).
- There is a "refresh" interval in which the client verifies that the source port is still valid.
- This interval is randomly varied by the Teredo service.
- Source ports can be prone to change and it is important for the Teredo server to know how to reach back to the client.
- Teredo acts almost like a dynamic port forwarding service that keeps track of both the public IP address and the source port of the client.
- By keep tracking of the source port and the IP this allows the Teredo server to reach directly back to the client, essentially bypassing NAT without any configuration required.
Teredo doesn't seem to play very nicely with symmetric NAT.
- Symmetric NAT randomly changes the "outside" source port per session
- First the IP address is changed from the source's non-routable address to the public IP address.
- Next the source port is randomly changed, with the mapping existing only in the router's memory.
- When the communication is complete the source port is no longer in use
- A new, random source port is chosen for the next session.
Somehow Teredo in Windows Vista and newer overcomes this, but I have not yet found a clear explanation for how.
Please read the IETF RFC on Teredo for further detail.
Note: I realize that this topic is quite old, but it is currently the top hit on SuperUser's internal search for "What is Teredo Tunneling". I wanted to provide a more generic answer since that is what I was seeking when I came here.