| IPv6 Network - 6to4 Under Windows | | Print | |
IPv6 Network - 6to4 Under Windows
There is no need to specifically enable 6to4 under Windows XP. When IPv6 is installed, the system automatically sets up a 6to4 pseudo interface if a public (non-RFC 1918) IPv4 address is available. So packets to 6to4 addresses are directly tunneled to their destination in IPv4, as long as the system has a regular IPv4 address. Additionally, if there is no other IPv6 connectivity, Windows installs one or more IPv6 default routes that point to 6to4 relays.
Rather than blindly installing a default route toward the RFC 3068 anycast address, Windows looks up the name 6to4.ipv6.microsoft.com in the DNS, transforms the resulting IPv4 addresses into 6to4 addresses, and pings them. Default routes and accompanying metrics (“Met” in the example below) are installed, depending on the replies to these ping packets. (Although it seems that any ICMP message, not just an ICMP Echo Reply, will do.) The default route with the lowest metric is used. A metric of 2147483648 (231) means the relay router is unreachable and the route can’t be used. Listing 3-1 shows the relevant netsh output with a 6to4 prefix based on the IPv4 address 223.224.225.226.
Listing 3-1. Listing Addresses and Routes Using the netsh Command
C:\>netsh interface ipv6 show address
Interface 3: 6to4 Tunneling Pseudo-Interface
Addr Type DAD State Valid Life Pref. Life Address
-------- --------- ----------- ----------- -----------------------
Other Preferred infinite infinite 2002:dfe0:e1e2::dfe0:e1e2
C:\>netsh interface ipv6 show routes
Querying active state...
Publish Type Met Prefix Idx Gateway/Interface Name
------- ------- ---- -------- --- ---------------------
yes Manual 1191 ::/0 3 2002:836b:213c:1:e0:8f08:f020:8
yes Manual 1041 ::/0 3 2002:c058:6301::c058:6301
yes Manual 1001 2002::/16 3 6to4 Tunneling Pseudo-Interface
The netsh command can also be used to change the name and settings for the 6to4 relay (type netsh, interface ipv6 6to4, and then help for more information), but the mechanism whereby Windows uses a domain name to determine the 6to4 relays can’t be turned off.
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