Windows 7 / Networking

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IPv6 address types

There are no broadcast transmissions in IPv6, and therefore no broadcast addresses, as in IPv4. IPv6 supports three types of transmissions, as follows:

• Unicast: Provides one-to-one transmission service to individual interfaces, including server farms sharing a single address
• Multicast: Provides one-to-many transmission service to groups of interfaces identified by a single multicast address
• Anycast: Provides one-to-one-of-many transmission service to groups of interfaces, only the nearest of which (measured by the number of intermediate routers) receives the transmission IPv6 scopes

In IPv6, the scope of an address refers to the size of its functional area. For example, the scope of a global unicast is unlimited, the entire Internet. The scope of a link-local unicast is the immediate link; that is, the local network. The scope of a unique local unicast consists of all the subnets within an organization.

IPv6 also supports several address types, as described in the following sections.

GLOBAL UNICAST ADDRESSES

A global unicast address is the equivalent of a registered IPv4 address, routable worldwide and unique on the Internet.

LINK-LOCAL UNICAST ADDRESSES

In IPv6, systems that assign themselves an address automatically create a link-local unicast address, which is essentially the equivalent of an APIPA address in IPv4. All link-local addresses have the same network identifier: a 10-bit prefix of 11111110 010 followed by 54 zeros, resulting in the following network address:

fe80:0000:0000:0000/64

In its more compact form, the link-local network address is as follows:

fe80::/64

Because all link-local addresses are on the same network, they are not routable and systems possessing them can only communicate with other systems on the same link.

UNIQUE LOCAL UNICAST ADDRESSES

Unique local unicast addresses are the IPv6 equivalent of the 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 private network addresses in IPv4. Like the IPv4 private addresses, unique local addresses are routable within an organization. Administrators can also subnet them as needed to support an organization of any size.

Many sources of IPv6 information continue to list site-local unicast addresses as a valid type of unicast, with a function similar to that of the private IPv4 network addresses. For various reasons, site-local unicast addresses have been deprecated, and although their use is not forbidden, their functionality has been replaced by unique local unicast addresses.

MULTICAST ADDRESSES

Multicast addresses always begin with an FP value of 11111111, in binary, or ff in hexadecimal.

ANYCAST ADDRESSES

The function of an anycast address is to identify the routers within a given address scope and send traffic to the nearest router, as determined by the local routing protocols. Organizations can use anycast addresses to identify a particular set of routers in the enterprise, such as those that provide access to the Internet. To use anycasts, the routers must be configured to recognize the anycast addresses as such.