Internet Protocol version 6 (IPv6) is the set of protocols that will replace
today's IPv4. IPv6 offers many benefits necessary to support the Internet's
continuing expansion—most notably an expanded address space that overcomes
pressures in regions such as Africa, Asia, China, and the Middle East. Temporary
solutions such as Network Address Translation (NAT)—although effective
in the short term—won't provide long-term help. Recognizing that IPv6
is the future, many governments are mandating that their systems and networks
support IPv6, including the US government, which has set a transition date of
June 30, 2008. If your company does business with entities that use (or plan
to use) IPv6, you'll feel the pressure to support IPv6, if only to support communications
between your company and your partners. Simply put, IPv6 might become a competitive
advantage.
In this first part of a three-part series, I
describe IPv6 addressing in detail, focusing
on how its addressing scheme works. I also
describe some of the new features of IPv6, as
well as some of the reasons you should care
about it—even if you don't plan on implementing it in the near future. In two future articles,
I'll describe how to install IPv6 onto Windows
Server 2003 and Windows XP, and how to
configure interfaces with addresses and enable
DNS resolution. I'll also describe in detail how
to configure your systems and networks to use
IPv6 and IPv4 together while you transition to
an all-IPv6 network. Finally, I'll look into strategies for using IPv6 over the IPv4 Internet if your
ISP doesn't support IPv6. But first, we need to
lay down a foundation.
Windows Support for IPv6
Almost every modern OS supports IPv6 out of the box. In fact, you're probably
running IPv6 on your networks without even realizing it. Microsoft supports
IPv6 in Windows Vista, Windows 2003, XP SP1 and later, and Windows CE .NET 4.1
and later.
Windows Server 2008 will also support IPv6. Microsoft Research produced an
IPv6 stack for Windows 2000 and Windows NT, but it isn't supported. To obtain
the stack, see the Learning Path online.
Only Vista has IPv6 enabled "out of the box." If you have Vista installed on
your network, you're running IPv6. Vista will configure link-local addresses
in the absence of IPv6 infrastructure hardware such as DHCP servers, IPv6-capable
routers, and so on. Once enabled, XP will function as an IPv6 client, letting
you conduct many common communications (e.g., Web browsing using HTTP or HTTPS)
over IPv6. Windows 2003 also supports IPv6 in most communications.
IPv6 Addressing
IPv6 gives you a whole new means of uniquely addressing a node (or end system).
In IPv6, there are 128 bits available to uniquely identify a node. IPv4 offers
32 bits, for a total of more than 4 billion possible combinations, but far fewer
are practically available because of the way address space has been organized.With
128 bits, we'll have sufficient addresses for the next millennium—even
given the way addresses are allocated.
Before I discuss the allocation and use of IPv6 addresses, it's helpful to
understand the format that's used to represent them. Whereas IPv4 uses a dotted-decimal
system (e.g., 192.168.16.10), IPv6 uses a different format. An IPv6 address
is split into eight 16-bit blocks: Each block is represented by four hexadecimal
digits, and each block is separated by a colon (:)—for example, 2001:0000:0000:e388:0092:
fb7f:a827:fad6. Within each block, leading zeroes can be omitted so that the
address can be read as 2001:0:0:e388:92: fb7f:a827:fad6. Also, blocks of zeroes
can be omitted, so that the address can be further simplified as 2001::e388:92:fb7f:a827:fad6.
Note the use of the double colon to represent the blocks of zeroes. If you have
more than one block of consecutive zeroes in an address, only one block can
be omitted. (Otherwise, it would be impossible to reconstruct the original address.)
Currently, three types of IPv6 addresses can
be allocated to a node: unicast, multicast, and
anycast. A unicast address uniquely identifies
a single interface (or network connection) on
a node (or a virtual interface on clustered systems). A multicast address is similar to an IPv4
multicast address and can be shared by several
interfaces on several nodes. A packet with a
multicast destination address is delivered to all
interfaces on all nodes that share the address.
However, a packet with an anycast destination address is delivered to only one interface:
the nearest interface to the sending interface.
Regardless of type, the address identifies an
interface on a node—not the node itself. A node
will likely have multiple IPv6 addresses, even if
it has only one interface.
Unicast Addresses
Each interface can have more than one unicast address. A unicast address can
be an Aggregatable Global Unicast Address (aka global address), or a LocalUse
Unicast Address.
Global address. A global address is unique to the interface it's
assigned to and can be used to reach that interface from any other interface.
Global IPv6 addresses are hierarchical and contain routing information. Figure
1 shows the format of a global address. A unicast address's first three
bits—called the Format Prefix (FP)—are always 001. FPs can be
of varying length (e.g., the multicast FP is eight bits in length). The next
thirteen bits comprise the TopLevel Aggregation Identifier (TLA ID). This ID
is allocated to top-level ISPs, of which there can be 8,192.
Next in the address is a reserved field—
eight bits in length and designed for future
expansion of the TLA ID. The next field in the
address, the Next-Level Aggregation Identifier
(NLA ID), is 24 bits in length and is used by
the top-level ISP to organize networks or to
support second-tier ISPs, each of which would
have one or more NLA IDs assigned to them.
These combined 48 bits uniquely identify
a site belonging to the top-level or second-tier
ISP's customer. Sites are determined by geography. For example, an international company
might have many sites. Each site's IPv6 connection will have a 48-bit address unique to
the site. Each site can use the next sixteen bits
in the address—called the Site-Level Aggregation Identifier (SLA ID)—to divide the site into
subnets. Each site can have 65,535 subnets.
Alternatively, if a company has multiple sites but
only one IPv6 connection via an ISP, it can use
the SLA ID to route between the sites and to the
connection. The last field in the global address
is the Interface ID, which is 64 bits in length. This
field is similar to IPv4's host identifier, which
uniquely identifies the host on the network.
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