I understand that Tunnel Adapter LAN is for encapsulating IPv6 packets with an IPv4 header so that they can be sent across an IPv4 network.

Few queries popped up in my mind based on this :-

1. If i do 'ipconfig', Apart from ethernet adapter LAN details, I get a series of statments as below -

   Tunnel adapter Local Area Connection* 6
   Tunnel adapter Local Area Connection* 7
   Tunnel adapter Local Area Connection* 12
   Tunnel adapter Local Area Connection* 13
   Tunnel adapter Local Area Connection* 14
   Tunnel adapter Local Area Connection* 15
   Tunnel adapter Local Area Connection* 16
   

   Except for the *16, all the other Tunnel Adapter Local Area Connections show Media Disconnected.

   Why is the numbering for the Tunnel adapter LAN not sequential? It is like 6, 7, 12, 13, 14, 15, 16. A strange numbering scheme! I tried to figure it out by thinking of some arithmetic series. But, it does not seem to fit in. There is a huge gap between 7 and 12. Any ideas?

2. What is the need for so many Tunnel Adapter LAN connections? Can you tell me a scenario that requires all of those ?

3. I did ipconfig /all to get more information.

   From the listing, I understand that:

   • 16, 15, 14, 12 are Microsoft 6to4 Adapters
   • 13, 6 are isatap Adapters
   • 7 is Teredo Tunneling Pseudo-interface

   I understand that the above are for automatic tunneling so that the tunnel endpoints are determined automatically by the routing infrastructure.

   6to4 is recommended by RFC3056 for automatic tunneling that uses protocol 41 for encapsulation. It is typically used when an end-user wants to connect to the IPv6 Internet using their existing IPv4 connection.

   Teredo is an automatic tunneling technique that uses UDP encapsulation across multiple NATs. That is, It is to grant IPv6 connectivity to nodes that are located behind IPv6-unaware NAT devices

   ISATAP treats the IPv4 network as a virtual IPv6 local link, with mappings from each IPv4 address to a link-local IPv6 address. That is to transmit IPv6 packets between dual-stack nodes on top of an IPv4 network.

   That is, to put in simple words, ISATAP is an intra-site mechanism, while the 6to4 and Teredo are for inter-site tunnelling mechanisms.

   It seems that Teredo should alone enabled by default in Vista, But my system does not show it to be enabled by default. Interestingly, it shows a 6to4 tunnel adapter (Tunnel adapter LAN connection 16) to be enabled by default? Any specific reasons for it?

4. If i do ipconfig /all, why is only one Teredo present while four 6to4 are present ?

I searched the internet for answers to the above queries, but I am unable to find clear answers.