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IPv6 traffic between nodes in different sites across the Internet (6to4)

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

IPv6 traffic between nodes in different sites across the Internet (6to4)

6to4 is a tunneling technique that is described in RFC 3056. When 6to4 is used, IPv6 traffic is encapsulated with an IPv4 header before it is sent over the IPv4 Internet.

6to4 uses the global address prefix of 2002:WWXX:YYZZ::/48, where WWXX:YYZZ is both the Next Level Aggregation ID (NLA ID) portion of a global address and the colon-hexadecimal representation of a public IPv4 address (w.x.y.z) that is assigned to the site or host. The complete 6to4 address of a 6to4 host is 2002:WWXX:YYZZ:[SLAID]:[InterfaceID].

RFC 3056 defines the following:

  • 6to4 host

    An IPv6 host that is configured with at least one 6to4 address.

  • 6to4 router

    An IPv4/IPv6 router that forwards 6to4-addressed traffic both between the 6to4 hosts within a site and to other 6to4 routers or 6to4 relay routers on the IPv6 Internet.

  • 6to4 relay router

    An IPv4/IPv6 router that forwards 6to4-addressed traffic between 6to4 routers on the Internet and hosts on the IPv6 Internet.

When you use 6to4 hosts, an IPv6 routing infrastructure within 6to4 sites, a 6to4 router at site boundaries, and a 6to4 relay router, the following types of communication are possible:

  1. A 6to4 host can communicate with another 6to4 host within the same site.

    This type of communication is available through the IPv6 routing infrastructure, which provides reachability to all hosts within the site.

  2. A 6to4 host can communicate with 6to4 hosts in other sites across the IPv4 Internet.

    This type of communication occurs when a 6to4 host forwards IPv6 traffic, which is destined to a 6to4 host in another site, to the local site 6to4 router. The local site 6to4 router encapsulates the IPv6 traffic with an IPv4 header and sends it to the 6to4 router at the destination site on the Internet. At the destination site, the 6to4 router removes the IPv4 header and forwards the IPv6 packet to the appropriate 6to4 host by using the IPv6 routing infrastructure of the destination site.

  3. A 6to4 host can communicate with hosts on the IPv6 Internet.

    This type of communication occurs when a 6to4 host forwards IPv6 traffic, which is destined for an IPv6 Internet host, to the local site 6to4 router. The local site 6to4 router encapsulates the IPv6 traffic with an IPv4 header and sends it to a 6to4 relay router that is connected to both the IPv4 Internet and the IPv6 Internet. The 6to4 relay router removes the IPv4 header and forwards the IPv6 packet to the appropriate IPv6 Internet host by using the IPv6 routing infrastructure of the IPv6 Internet.

All of these types of communication use IPv6 traffic without the requirement of obtaining either a direct connection to the IPv6 Internet or an IPv6 global address prefix from an Internet service provider (ISP).

Support for 6to4 hosts and routers is provided in the IPv6 Helper service that is included with the IPv6 protocol for Windows Server 2003 family and Windows XP. The IPv6 Helper service:

  • Automatically configures 6to4 addresses on the interface (named 6to4 Pseudo-Interface or interface index 3) that is used for all public IPv4 addresses that are assigned to interfaces on the computer. For more information, see Single subnet with link-local addresses.

  • Automatically creates a 2002::/16 route that forwards all 6to4 traffic with the 6to4 Pseudo-Interface (interface index 3). All traffic forwarded by this host to 6to4 destinations is encapsulated with an IPv4 header.

  • Automatically performs a Domain Name System (DNS) query for the name 6to4.ipv6.microsoft.com to obtain the IPv4 address of the Microsoft 6to4 relay router on the Internet. You can use the netsh interface ipv6 6to4 set relay command to specify which DNS name to query. For more information, see IPv6 utilities.

With the IPv6 Helper service configuration, computers are automatically configured as a 6to4 host when:

  • The host is running the IPv6 protocol.

  • The host is configured with an IPv4 public IP address.

  • The host does not receive a Router Advertisement from an IPv6 router.

A 6to4 host can perform its own tunneling to reach either 6to4 hosts in other sites or hosts on the IPv6 Internet.

For more information about connecting to the IPv6 Internet, see Connecting to the IPv6 Internet.

If Internet Connection Sharing (ICS) is enabled on an interface that is assigned a public IPv4 address, the IPv6 Helper service:

  • Enables routing on the private interface.

  • Sends Router Advertisements that contain 6to4 address prefixes, which are based on the public IPv4 address of the public interface. The SLA ID in the 6to4 address prefix is set to the interface ID of the interface on which the advertisements are sent.

By enabling ICS, you can use a computer running the IPv6 protocol for Windows XP as a 6to4 router, which is capable of both encapsulating and forwarding 6to4 traffic to other 6to4 hosts or sites on the Internet, and forwarding IPv6 Internet traffic to a 6to4 relay router on the Internet.

The following illustration shows how 6to4 is used to communicate between two 6to4 sites.

Using 6to4 to communicate between two 6to4 sites

Each site uses a computer with ICS enabled on the public interface to create a 6to4 router. Host computers on the private network segments receive the Router Advertisement that is sent by their site's 6to4 router and contains a 6to4 address prefix. As the result, two 6to4 hosts can communicate by using 6to4 addresses over the Internet.

For additional information about configurations, see IPv6 Configurations.

For information about using IPv6 in a test lab, see Setting up an IPv6 Test Lab.

Note

  • Internet Connection Sharing and Network Bridge are not included in Windows Server 2003, Web Edition; Windows Server 2003, Datacenter Edition; and the Itanium-based versions of the original release of the Windows Server 2003 operating systems.

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