Experiencing IPv6 with Windows XP Part 1 Making your XP talk IPv6

Windows, a popular consumer OS series, finally got IPv6 communication capability in Windows XP. That has brought this new IP protocol much closer to us. Let’s have a taste of IPv6 with Windows XP.

IPv6 has been included in both Windows XP Professional, and Home Edition. At first, it was positioned as developer release, which meant no support for ordinary users. But Microsoft announced official support for IPv6 with Service Pack-1 (XP SP-1). XP SP-1 has some additional functionalities in install and IPv6 commands. I will basically follow procedures common to XP and XP SP-1 below, and add explanation about the differences between two versions.


Installing IPv6

Normal OS install process does not automatically enable IPv6. You need to show command prompt (remember?) and type:

Ipv6 install

‹Figure 1 Installing IPv6 and displaying information›

XP SP-1 added GUI install process, much like adding other networking protocols. Go to Network Component and choose Protocol, then select Microsoft IPv6 Developer Edition.

You need to use command prompt for other settings and use “ipv6” command family. Here is another addition in XP SP-1. The new version added “netsh interface ipv6” command family for virtually the same functionality. Microsoft says it will discontinue use of ipv6 commands in favor of netch interface ipv6 commands. But for now, let’s use ipv6 command family because they can be commonly used for Windows XP and XP SP-1. Some ipv6 commands and corresponding netsh interface ipv6 commands are listed at the bottom of this article.

Figure 1 shows the process of installing IPv6, without connecting any interfaces to network, and then displaying network interface information by:

ipv6 if

You can see that Link-Local addresses are displayed for Interface 5 (wireless interface) and Ethernet interface.

Now, let’s plug an Ethernet cable in your Ethernet port, and try the same command:

Ipv6 if

Now you see Global IPv6 Address configured for Interface 4, shown under “preferred global” (Figure 2). What happened was that the computer automatically created the global IPv6 address on its own, without any DHCP server, or without you configuring anything.

‹Figure 2 Connected to IPv6 native network›

Knowing different types of addresses

We found that many addresses are configured on one interface. IPv6 has a concept called “scope,” and has three types of addresses according to the scope: Link-Local, Site-Local, and Global Address. One interface can have all these addresses, and they are used for different purposes.

Link-Local Address is the first address configured when an interface attached to the network, but it is effective only on the same link. In other words, communication with address do not go beyond router. But Link-Local Address is not used for data communications, it is used for control functions. Site-Local Address is limited for use in a site, for internal communication in a company. But usually, IPv6 connected computers use Global Address.


Automatically created address

When you connect to global IPv6 Internet with Windows XP, the computer automatically create Global IPv6 Address for the connected network interface immediately. The computer does not ask any server. The only information it gets from others is “Network Prefix,” The number of network the computer resides on. It combines that with “Interface ID,” which the computer creates on its own. 64bit Network Prefix and 64bit Interface ID makes 128bit Global IPv6 Address.

The information used by the computer for making Interface ID is MAC address, in the case of Ethernet adapter. MAC address is usually 48bit address shown in hexadecimal form. First 24bit is vendor ID, registered to IEEE. Latter 24bit is unique ID (serial number) assigned by the vendor. So MAC address is supposed to be unique in the world.

In Figure 2, you can see, “link layer address 08-00-46-45-07-00.” This is the MAC address of the Ethernet adapter. Then look at “preferred global (public).” It says “2001:2a0:4ff:0:a00:46ff:fe45:700.” The latter half of the address is created automatically from MAC address.

MAC address is 48bit, 16bit short for Interface ID, which is 64bit. So some tricks are used, like inserting “fffe” in the middle.

Then how is Network Prefix obtained? This is where Link-Local Address comes in. With Link-Local Address, first 64bit is always “fe:/64.” Computer just connected to the network first creates Link-Local Address by combining “fe:/64” and Interface ID computed from MAC address of the connected interface. It confirms that the same address is not used on the same link, just in case. Then it becomes ready to communicate.

On the other hand, router sends message called Router Advertisement (RA) periodically. This message contains network prefix information. The connected computer receives this information and combines this with Interface ID to form Global IP Address.

Computer can send message called Router Solicitation (RS) to request prefix information. At this point, the computer has no knowledge of router address, but it uses a multicast address “ff02::2,” which any routers are required to receive. The computer sends RS message with this as destination address, and the nearest router sends back RA.