Windows – networking tunnel adapter connections

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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.

Best Answer

Disclaimer: I'd never even heard of Teredo or ISATAP until I read your post.

That said, I'll take a swing at them:

  1. My guess it that 8-11 are the 'other ends' of 12-16. Or maybe the bridge ends of 1-5 into the virtual network and NAT that is being set up.

  2. v6 interfaces need to be separately addressable from v4 interfaces, so that's 5 more (given you've got 5 physical interfaces - you didn't actually specify). Add another couple to serve as bridges and NAT bottlenecks and those numbers seem reasonable.

  3. Assuming a v4 environment is still a reasonable default.

  4. One Teredo per physical interface perhaps? Just because you (likely) have them bonded or something doesn't mean they have to be.

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