Understanding Unicast Addresses
Unicast addresses are addresses that identify a single interface. IPv6 has several types of unicast addresses:
- Global unicast address An address that is globally routable over the IPv6-enabled
portion of the Internet. Therefore, the scope of a global address is the entire Internet,
and global addresses in IPv6 correspond to public (non-RFC 1918) addresses used in
IPv4. The address prefix currently used for global addresses as defined in RFC 3587 is
2000::/3, and a global address has the following structure:
- The first 48 bits of the address are the global routing prefix specifying your organization's site. (The first three bits of this prefix must be 001 in binary notation.) These 48 bits represent the public topology portion of the address, which represents the collection of large and small Internet service providers (ISPs) on the IPv6 Internet and which is controlled by these ISPs through assignment by the Internet Assigned Numbers Authority (IANA).
- The next 16 bits are the subnet ID. Your organization can use this portion to specify up to 65,536 unique subnets for routing purposes inside your organization's site. These 16 bits represent the site topology portion of the address, which your organization has control over.
- The final 64 bits are the interface ID and specify a unique interface within each subnet.
- Link-local unicast address An address that can be used by a node for communicating
with neighboring nodes on the same link. Therefore, the scope of a link-local address
is the local link on the network; link-local addresses are never forwarded beyond
the local link by IPv6 routers. Because link-local addresses are assigned to interfaces
using IPv6 address autoconfiguration, link-local addresses in IPv6 correspond to Automatic
Private IP Addressing (APIPA) addresses used in IPv4 (which are assigned from
the address range 169.254.0.0/16). The address prefix used for link-local addresses is
FE80::/64, and a link-local address has the following structure:
- The first 64 bits of the address are always FE80:0:0:0 (which will be shown as FE80::).
- The last 64 bits are the interface ID and specify a unique interface on the local link.
- Unique local unicast address Because a site-local address prefix can represent
multiple sites within an organization, it is ambiguous and not well suited for intraorganizational
routing purposes. Therefore, RFC 4193 currently proposes a new type of
address called a unique local unicast address. The scope of this address is global to all
sites within the organization, and using this address type simplifies the configuration
of an organization's internal IPv6 routing infrastructure. A unique local address has the
- The first seven bits of the address are always 1111 110 (binary) and the eighth bit is set to 1, indicating a unique local address. This means that the address prefix is always FD00::/8 for this type of address.
- The next 40 bits represent the global ID, a randomly generated value that identifies a specific site within your organization.
- The next 16 bits represent the subnet ID and can be used for further subdividing the internal network of your site for routing purposes.
- The last 64 bits are the interface ID and specify a unique interface within each subnet.
Note Site-local addresses have been deprecated by RFC 3879 and are replaced by unique local addresses.
In this tutorial:
- Deploying IPv6
- Understanding IPv6
- Understanding IPv6 Terminology
- Understanding IPv6 Addressing
- Understanding IPv6 Prefixes
- Understanding IPv6 Address Types
- Understanding Unicast Addresses
- Identifying IPv6 Address Types
- Understanding Interface Identifiers
- Comparing IPv6 with IPv4
- Understanding IPv6 Routing
- How IPv6 Routing Works
- IPv6 Route Determination Process
- IPv6 Routing Table Structure
- Understanding ICMPv6 Messages
- Understanding Neighbor Discovery
- Understanding Address Autoconfiguration
- Understanding Name Resolution
- Understanding Name Queries
- Understanding Name Registration
- PTR Records and IPv6
- IPv6 Enhancements in Windows 7
- Summary of IPv6 Enhancements in Windows 7
- Configuring and Troubleshooting IPv6 in Windows 7
- Configuring IPv6 in Windows 7 Using the User Interface
- Configuring IPv6 in Windows 7 Using Netsh
- Other IPv6 Configuration Tasks
- Enabling or Disabling IPv6
- Disabling Random Interface IDs
- Resetting IPv6 Configuration
- Displaying Teredo Client Status
- Troubleshooting IPv6 Connectivity
- Planning for IPv6 Migration
- Blocking Teredo
- Understanding ISATAP
- Migrating an Intranet to IPv6
- Step 1: Upgrading Your Applications and Services
- Step 2: Preparing Your DNS Infrastructure
- Step 3: Upgrading Your Hosts
- Step 4: Migrating from IPv4-only to ISATAP
- Step 5: Upgrading Your Routing Infrastructure
- Step 6: Upgrading Your DHCP Infrastructure
- Step 7: Migrating from ISATAP to Native IPv6
- The Advantages of IPv6
- Address Resolution in IPv6