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Chapter 13

6to4

At the end of this chapter, you should be able to do the following:

Define the address format, encapsulation, and intended use of the 6to4 IPv6 transition technology.

Describe how the IPv6 protocol in Windows Server 2008 and Windows Vista supports 6to4 as a host, host/router, and router.

List and describe the routes on a 6to4 host, a 6to4 host/router, a 6to4 router, and the IPv6 routers on the IPv6 Internet that make 6to4-based communication possible.

Describe how 6to4-tunneled communication works between 6to4 hosts, 6to4 host/ routers, 6to4 routers on the IPv4 Internet, and IPv6 hosts on the IPv6 Internet.

Describe how to manually configure a computer running Windows Server 2008 or Windows Vista as a 6to4 router.

6to4 Overview

6to4 is an address assignment and router-to-router, host-to-router, and router-to-host automatic tunneling technology defined in RFC 3056 that is used to provide unicast IPv6 connectivity between IPv6 sites and hosts across the IPv4 Internet. 6to4 treats the entire IPv4 Internet as a single link.

Figure 13-1 shows the structure of a 6to4 address.

2002

WWXX : YYZZ

Subnet ID

Interface ID

 

 

 

 

16 bits 32 bits 16 bits 64 bits

Figure 13-1 The structure of a 6to4 address

The 6to4 address consists of the following:

2002::/16 is the address space reserved for 6to4.

WWXX:YYZZ is the colon hexadecimal representation of a public IPv4 address (w.x.y.z) assigned to a site or host on the IPv4 Internet. Public IPv4 addresses are directly reachable on the IPv4 Internet.

Subnet ID is used within the site of an organization to number individual subnets.

Interface ID identifies a node on a subnet within an organization.

295

296 Understanding IPv6, Second Edition

There is a common misconception that before you can begin communicating between IPv6-enabled sites of an organization over a public network or connecting to public resources on the IPv6 Internet, you need a direct connection to the IPv6 Internet and a 48-bit global address prefix from an Internet service provider (ISP). Although this should eventually be done, 6to4 allows you to do the following:

Create and use 48-bit global IPv6 address prefixes (2002:WWXX:YYZZ::/48) based on public IPv4 addresses that are assigned to your organization.

Connect IPv6-capable portions of your intranet together by tunneling IPv6 traffic over the IPv4 Internet.

Connect to IPv6-only resources on the IPv6 Internet.

6to4 allows you to assign global IPv6 addresses within your organization and to reach locations on the IPv6 Internet without requiring that you obtain a direct connection to the IPv6 Internet or an IPv6 global address prefix from an ISP.

6to4 Tunneling

6to4 traffic sent across the IPv4 Internet is tunneled or encapsulated with an IPv4 header, also known as IPv6-over-IPv4 traffic. For the details of IPv6-over-IPv4 traffic, see Chapter 11, “IPv6 Transition Technologies.” This tunneling is automatically done by a 6to4 tunneling interface on the sending host or a forwarding router. The 6to4 tunneling interface treats the entire IPv4 Internet as a single link layer, in much the same way as Ethernet. In the case of 6to4, the link layer encapsulation is IPv4.

The IPv6 protocol for Windows Server 2008 and Windows Vista creates and enables a 6to4 tunneling interface when there are no other forms of IPv6 connectivity—that is, there are no router advertisements received from native IPv6 or Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) routers—and there is a public IPv4 address assigned to one of the interfaces of the computer. The name of the interface depends on the computer’s configuration. All tunneling interfaces by default have an asterisk (*) in their name, such as “Local Area Connection* 6”. To determine the name of the 6to4 tunneling interface, display the TCP/IP configuration with the ipconfig /all command. The 6to4 tunneling interface has an asterisk in its name and has the description “Microsoft 6to4 Adapter” or “6TO4 Adapter.”

The IPv6 protocol for Windows Server 2008 and Windows Vista automatically assigns the 6to4 tunneling interface the address 2002:WWXX:YYZZ::WWXX:YYZZ, in which WWXX:YYZZ is the colon hexadecimal notation of a public IPv4 address assigned to an interface of the computer. If there are multiple public IPv4 addresses, the 6to4 tunneling interface will be assigned multiple addresses of the form 2002:WWXX:YYZZ::WWXX:YYZZ. For example, for a computer running Windows Vista that is assigned the public IPv4 address 131.107.0.1, IPv6 assigns the address 2002:836B:1::836B:1 to the 6to4 tunneling interface. This special type of 6to4 address, which uses a Subnet ID of 0 and an interface ID

of ::WWXX:YYZZ, is for used for Windows-based 6to4 routers or host/routers. For more information, see “6to4 Components” in this chapter.

Chapter 13 6to4

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To disable 6to4, set the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ tcpip6\Parameters\DisabledComponents registry value to 0x2 (DWORD) and then restart the computer.

Note IPv6 for Windows Server 2003 and Windows XP creates a 6to4 tunneling interface that was always named “6to4 Tunneling Pseudo-Interface.”

6to4 Tunneling Example

Host A running Windows Vista has a single local area network (LAN) interface and is configured with the public IPv4 address of 131.107.0.1. Host B running Windows Vista has a single LAN interface and is configured with the IPv4 address of 157.54.0.1. IPv6 on Host A automatically configures the 6to4 address of 2002:836B:1::836B:1 on its 6to4 tunneling interface (named “Local Area Connection* 6”), and Host B automatically configures the 6to4 address of 2002:9D36:1::9D36:1 on its 6to4 tunneling interface (named “Local Area Connection* 5”). Both Host A and Host B are directly connected to the IPv4 Internet. Figure 13-2 shows this example configuration.

Host A 2001:836B:1::836B:1

IPv4 Internet

Host B 2002:9D36:1::9D36:1

Figure 13-2 An example 6to4 configuration

When Host A sends IPv6 traffic to Host B destined to Host B’s 6to4 address, the source and destination addresses for the IPv6 and IPv4 headers are as listed in Table 13-1.

To test connectivity between 6to4 hosts, you can use the Ping tool (subject to Windows Firewall exceptions for Internet Control Message Protocol for IPv6 [ICMPv6] traffic). For example, to ping Host B at its 6to4 address from Host A, you use the following command:

ping 2002:9d36:1::9d36:1

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