In-Depth

Changing Addresses

Not too long ago, there were real fears that we’d run out of Internet Protocol (IP) addresses for our networks. That’s not likely to happen with IPv6.

THE TCP/IP PROTOCOL SUITE will save us from the scarcity of public IP addresses. Windows XP contains Microsoft’s first IPv6 implementation, and Windows .NET Server 2003 will contain the first production-ready version of that implementation. Other network devices—such as routers, switches and so forth—are receiving their IPv6-compatible updates in a slow but steady stream. Within a year or two, most network devices should be capable of handling IPv6 traffic. So what’s the big deal about IPv6 and why should you care?

2128 Addresses
When the Internet’s popularity exploded, folks became concerned about the availability of IP addresses. After all, IPv4’s four-octet address space could only support about 4.2 billion addresses. IPv6 (by the way, the version of TCP/IP you’ve been using is IPv4; version 5 was assigned to another protocol), uses an entirely new addressing scheme that can support more than 2128 addresses or about 665 million quadrillion addresses for every square meter of the earth’s surface. That should be plenty! IPv6 addresses look different, too. For one, they’re hexadecimal. For another, they’re very long: 21DA:00D3:0000:2F3B:02AA: 00FF:FE28:9C5A is an example. You can use a form of shorthand, which removes contiguous blocks of zeros to make IPv6 addresses a bit easier to read. For example, 21DA:D3:0:2F3B:2AA:FF:FF228:9C 5A is a simplified version of the first example. Notice that all leading zeros within the address have been removed. You can simplify one step further and remove any standalone zeros: 21DA:D3:: 2F3B:2AA:FF:FF228:9C5A. Note the double colon standing in where there used to be four zeros.

Even simplified, though, you’re looking at a pretty long IP address, which means you’ll be relying even more on name-resolution technologies, like DNS, so you can work with easier-to-remember host names instead of long strings of letters and numbers. You’ll be happy to learn that the DNS specifications have been extended to include a new record type, “AAAA,” which supports IPv6 addresses, and that .NET’s DNS server software supports these records. I’ll discuss DNS a bit more toward the end of this article.

Like IPv4, which breaks its address range into five distinct classes (Classes A, B and C being the most common), IPv6 breaks its tremendous address space into distinct blocks. For example, about 1/256th of the addresses are used for multicast applications, another 1/1,024th for local site unicast addresses (more on those in a bit) and so on. All told, about 15 percent of the IPv6 addresses are used for unicast, or single-host, addresses. A huge portion of the addresses is reserved for future use, making IPv6 extensible for applications we can’t even imagine today.

What about subnet masks? A major component of today’s IP networks, IPv6 doesn’t use them at all. Instead, IPv6 uses prefixes to tell it which portion of an address represents the network ID. These prefixes are similar to the Classless Interdomain Routing (CIDR) notation you may use in IPv4. For example, 21DA:D3:0:2F3B::/64 indicates a 64-bit subnet mask.

Types of Addresses
IPv4 really only had two types of addresses: Single-host addresses and a special broadcast address. A range of single-host addresses is set aside for multicast use, but that range was kind of an add-on to the basic IPv4 addressing scheme. IPv6, on the other hand, has three distinct types of addresses:

  • Unicast addresses represent a single network interface, such as the network adapter in your laptop. Traffic sent to a unicast address is received only by the host using that address, just like the IP addresses we use today.
  • Multicast addresses can be used to represent multiple network interfaces, such as every network adapter in every computer participating in an online conference. Individual computers can subscribe to multicast addresses to take part in multicast traffic, in much the same way that individual people can dial into a traditional conference call. Traffic sent to a multicast address is received by every computer using the address.
  • Anycast addresses allow traffic to be delivered to the nearest network interface using the anycast address, so that only one recipient receives the traffic, even if multiple computers have subscribed to the anycast address. Anycasts help simplify routing decisions on complex networks and are kind of a cross between a unicast address and a multicast address.

Notice that IPv6 doesn’t define a specific broadcast address like IPv4 does. With IPv6, there’s really no such thing as a broadcast; instead, devices use multicasts to address multiple computers at once. IPv6 does define special multicast addresses to which all IPv6 network interfaces must subscribe, and these addresses can be used to duplicate the effects of a broadcast. There’s a special subnet-wide multicast address, a site-wide multicast address and so forth, so each IPv6 computer on a network will have a number of IPv6 addresses:

  • A link-local address, which provides communications within the same subnet. The link-local address is non-routable and is similar to the Automatic Private IP Addressing (APIPA) IPv4 network range, 169.254.0.0. .NET’s IPv6 network stack automatically generates a unique link-local address for each network adapter in the computer and will use this address to communicate with other computers on the local subnet. IPv6 routers can safely ignore all link-local traffic, because, by definition, it’s not intended for other subnets.
  • A site-local unicast address, which is unique within the network. This is basically the same as the private IPv4 address ranges, such as 192.168.0.0. Site-local unicast addresses aren’t routable on the Internet.
  • Optionally, a global unicast address, which is unique across the Internet. This is similar to the public IP address ranges used under IPv4. The Internet Assigned Numbers Authority (IANA) will continue to be responsible for issuing global IPv6 addresses to organizations to ensure uniqueness, just as they do for public IPv4 address ranges today. In most corporate environments, computers will only have a site-local unicast address; external devices like firewalls will also have a global address and perform Network Address Translation (NAT) between the internal site-local addresses and the Internet global addresses.
  • A local subnet multicast, which allows multicasts to all computers on a particular subnet.
  • A site-wide multicast, which allows multicasts to all computers within a particular site.
  • Perhaps a company-wide multicast, which would allow multicasts to all computers within a company, including computers at different geographic locations.
  • Any other multicast addresses the interface subscribes to for specific events such as an online conference.

Backward Compatibility
IPv6 has actually been around for several years, but it’s taking a long time for folks to adopt it, as it represents a major change in how networks run. Heck, until .NET comes out, we won’t even have a Windows operating system that can handle IPv6! Because the IPv6 conversion will undoubtedly take several more years, IPv6 provides robust backward compatibility with IPv4. For example, the IPv6 address 0:0:0:0:0:0:192.168.0.2 represents the IPv4 address 192.168.0.2 and can be expressed in shorthand as ::192.168.0.2. When an IPv6 computer sends information to a backward-compatible address, the computer encapsulates the IPv6 header information into a standard IPv4 packet, ensuring that the IPv6 information can be transported across an older IPv4 network. These compatibility addresses are used by computers that support both IPv6 and IPv4, which is the case for .NET computers that have IPv6 enabled.

Want to Know More About IPv6?

Sometimes, an IPv6 computer will need to contact a computer that only understands IPv4. In these cases, the IPv6 computer uses a mapped address, such as ::FF:192.168.10.5. This IPv6 representation of an IPv4 address tells the sending computer that the destination only supports IPv4 and that it should send pure IPv4 packets to that destination.

What’s in .NET?
.NET contains a pretty comprehensive IPv6 implementation. For example, the built-in DNS Client service and the DNS Server software support dynamic registration of IPv6 addresses. The new “AAAA” DNS record type contains IPv6 addresses. This new record type allows the same DNS server to perform IPv6 name resolution, as well as IPv4 name resolution, as IPv4 addresses are contained in “A” records.

.NET’s IPSec stack also supports IPv6 in a variety of configurations and includes the Ipsec6.exe tool, which allows you to manually configure IPv6-based security policies, associations and encryption keys. Windows Sockets has been updated to support both IPv4 and IPv6 connections, which means all Remote Procedure Call (RPC) traffic can run over IPv4 or IPv6. Internet Explorer, Telnet, FTP, IIS 6.0, file and print sharing, Windows Media Services and Network Monitor all support IPv6. Finally, .NET supports IPv6 routing through the use of:

netsh interface ipv6 route

This allows you to configure a server with static IPv6 routes, effectively turning the server into a rudimentary IPv6 router.

What .NET IPv6 Doesn’t Have
INET doesn’t contain a GUI for configuring IPv6. Instead, you’ll have to use:

netsh interface ipv6

from a command line, to configure IPv6. For example:

netsh interface ipv6 add address "Private" FE80::2

adds a new address to the network interface named Private. And finally, .NET doesn’t ship with an IPv6 DHCP server. There’s a specification for the DHCPv6 protocol, which provides fully automatic configuration of IPv6 addressing information, but Windows simply doesn’t include the server software that implements the protocol. Without DHCPv6, you’ll be back in the good old days of manual configuration for everything but the link-local address, which Windows’ IPv6 stack configures automatically. One piece of good news: IPv6 configuration doesn’t include a default gateway setting. Instead, IPv6 hosts listen for special broadcasts from IPv6-compatible routers and automatically select the nearest available router as their default gateway. This handy trick makes your network more self-healing, as computers can automatically discover alternate routers if their first choice fails.

Deploying IPv6
Most companies will deploy IPv6 to their boundary devices like routers, firewalls and so on first. Most newer editions of these devices already support IPv6 and simply require some minor configuration to make it active. Many Cisco devices, for example, include an IPv6 stack that’s disabled by default. You’ll also need to deploy a DHCPv6 server (perhaps Microsoft will release an add-on DHCPv6 server for .NET in the near future), and you’ll need to deploy an IPv6 stack to your client computers. .NET will have Microsoft’s first production-ready IPv6 stack. I expect an add-on to be available for Windows XP Professional, at least, and expect the next version of Windows to include an IPv6 stack. You may be out of luck for older operating systems, although Microsoft could decide to release an IPv6 stack for Win2K at some point.

Why Bother?
With technologies like NAT in everyday use on most networks, the feared shortage of IPv4 addresses is less of a worry than it first seemed. Still, IPv6 offers a lot more than nearly infinite addresses: It offers a whole new way to think about network traffic. Computers will suddenly have multiple addresses to work with, making multicast applications like video and audio streaming easier and more efficient.

The variety of scope-specific addresses, such as link-local and site-local addresses, makes it easier for routers to do their jobs, enabling routers to handle more network traffic than before. Scoped addresses might have interesting applications in other areas, too. For example, you might be able to target a software deployment for a specific subnet on your network, based on the computers’ subnet-specific multicast addresses. Pop-up messages might become more useful, as you’d be able to send an instant message to an entire site or to a specific subnet, based on the appropriate multicast address.

IPv6 has been a long time coming—and it’ll likely be a long time yet before we’re all using it—but it offers a lot of exciting possibilities for the network of the future.

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