IPv6 Overview
| The initial goal of IPv6 was simply to address the problem of IP address depletion that has become common with the older, familiar IPv4 protocol suite. As you'll see in a bit, IPv6 addresses that problem with a massive new addressing scheme that should provide ample addresses far into the future. However, once underway, the developers of IPv6 also decided to address some other problems that new and innovative uses of the Internet were making apparent, including broadcast and multicast support, security, addressing boundaries, and more. In this section, we'll provide you with an overview of how IPv6 works in general and some specifics about the IPv6 implementation in Windows Server 2003.
If you can't wait for the day when IPv6 becomes an everyday reality, don't hold your breath . Although the IT industry in general has committed to moving to IPv6, doing so is going to make the Year 2000 crisis look like a walk in the park. Nearly every single network device in the world, from desktop computers to servers, from routers to Web-capable cell phones, and many more, will have to be upgraded to support IPv6. Certainly, the process is well underway, with major vendors such as Microsoft and Cisco including IPv6 support in their new products. Additionally, IPv6 provides backward-compatibility with IPv4, enabling older devices to function while the transition is underway. Even so, the move to IPv6 remains slow (the protocol has existed for more than five years already), and it will likely be a few more years before you can forget everything you know about IPv4. IPv6 TutorialPerhaps the easiest place to begin a discussion on IPv6 is with addressing. Rather than the four-octet, dotted -decimal IP addresses you're accustomed to, such as 192.168.0.52 , IPv6 uses hexadecimal addresses like this: 21DA:00D3:0000:2F3B:02AA:00FF:FE28:9C5A . For simplification, you can remove any leading 0s for any segment of the address, resulting in something similar to this: 21DA:D3:0:2F3B:2AA:FF:FF228:9C5A . IPv6 addresses are roughly four times longer than IPv4 addresses, and, whereas IPv4 addresses provide for 4.2 billion possible addresses, IPv6 can support 3.4x10 38 addresses (that's like a trillion quadrillion quadrillion addresses, or about a million quadrillion addresses for every square meter of the earth's surface). Just as IPv4 addresses were divided into classes (Class A, Class B, and so forth), IPv6 addresses are also divided. For example, approximately 1/256 of the IPv6 address space is reserved for multicast addresses, another 1/1024 is reserved for local site unicast addresses, and so forth. About 15% of the address space is available for unicast, or single-host, addresses. Because so much of the address space is reserved for particular uses, and because IPv6 allows addresses to be compressed, or expressed in shorthand, so that 0s aren't displayed, you might find yourself working with addresses such as FF02::02 , which is a shortened version of FF02:0:0:0:0:0:0:2 . Basically, you just leave out all the contiguous 0s and include a double colon in their place, compressing the address down to a much more manageable size. You can remove only one contiguous series of 0s, meaning compressed addresses such as FF02::5::2 aren't legal.
In IPv4, you use a subnet mask to specify which portion of an IP address is the host address and which portion is the network address. IPv6 doesn't use subnet masks. Instead, it relies on a prefix to specify which portion of the address is the network's ID number. Prefixes are identical to the Classless Interdomain Routing (CIDR) notation you might already use for subnet masks. For example, 21DA:D3:0:2F3B::/64 specifies a 64-bit mask, which represents a particular subnet on a network. IPv6 supports three distinct types of addresses:
Notice that IPv6 does not define a broadcast address, like IPv4 does. Under IPv6, all broadcasts are conducted as multicasts. The IPv6 specification includes special multicast addresses to which all IPv6 interfaces must subscribe, enabling subnet-specific broadcasts, site-wide broadcasts, and so forth. IPv6 does define a couple of special addresses. The unspecified address , used in routing calculations, is simply :: , or 0:0:0:0:0:0:0:0 , which is equivalent to IPv4's 0.0.0.0 address. IPv6's loopback address is ::1 , which is equivalent to IPv4's 127.0.0.1 loopback address. To provide backward-compatibility with IPv4, IPv6 specifies compatibility addresses. For example, 0:0:0:0:0:0:192.168.0.2 supports the IPv4 address 192.168.0.2 and also can be expressed as ::192.168.0.2 . When these compatibility addresses are used, the computer encapsulates all IPv6 header information into an IPv4 packet, allowing the IPv6 packet to be carried by an older IPv4 network. Compatibility addresses are used by computers that support both IPv6 and IPv4. For an IPv6 computer to address an IPv4-only computer, it must used mapped addresses , such as 0:0:0:0:0:FFFF:192.168.10.5 , or simply ::FFFF:192.168.10.5 . This internal IPv6 representation of an IPv4 address tells the computer that, when sending packets to that destination, it must fall back to the pure IPv4 protocol and not attempt to send IPv6 packets. Interestingly, computers on an IPv6 network usually have multiple addresses, even if they have only a single network adapter. These addresses include
The purpose of these different addresses is to help conserve address space and to make routers' jobs easier. A major problem with IPv4 is that the simple volume of IP traffic makes it tough for routers to keep up because they must analyze a great deal of traffic simply to see whether that traffic needs to be routed. IPv6's use of specific classes of address, some of which are routable and some of which aren't, helps routers perform their tasks more efficiently . Also, computers won't necessarily have one of each type of address. For example, a computer within a large enterprise network might have a link-local and site-local address but no global address. Instead, only the network's boundary devicessuch as firewallswould use global addresses, performing the IPv6 version of NAT to provide Internet access to internal clients . There's plenty more to the IPv6 protocol, of course, including complex new packet headers, routing tables, and so on. For details, connect to www.microsoft.com/ipv6, where you'll find several detailed technical documents regarding IPv6. IPv6 in Windows Server 2003Windows Server 2003 contains the first production version of Microsoft's IPv6 stack (Windows XP includes a similar, prerelease version of the stack). The stack contains all the features to operate on a pure IPv6 network or a combined IPv4/IPv6 network, including
To install and configure the IPv6 stack on Windows Server 2003, follow these steps:
Unlike the IPv4 stack, which includes a complete GUI for configuring IP addresses and other information, IPv6 is configured entirely from the command line by using the netsh interface ipv6 command. For example, netsh interface ipv6 add address "Internal" AEB0::2 adds the address AEB0::2 to the network interface named Internal. Other commands enable you to add DNS server information, interfaces, routes, prefix policies, 6to4 tunnel settings, and so forth. Of course, configuring IPv6 settings from a command line is definitely a step backward, when everyone has become used to automatic configuration through DHCP. There is a specification for DHCPv6the IPv6 update to DHCPwhich provides full automatic configuration. Unfortunately, Windows Server 2003 does not include a DHCPv6-compatible DHCP service, nor does Windows Server 2003's IPv6 stack include DHCPv6 support. By default, Windows Server 2003's IPv6 stack creates a unique local-link address automatically (similar to APIPA in IPv4), removing a minor piece of manual configuration effort. Also, all IPv6 hosts listen for advertisement messages sent by IPv6 routers and use those messages to configure their default router, the location of a DHCPv6 server ( assuming one exists and the stack supports its use), and other information. On a network with multiple IPv6 subnets, you'll likely have to perform some manual configuration, especially if your routers aren't configured to send IPv6 router advertisements.
|
EAN: 2147483647
Pages: 136