Windows-IPv6 Addressing and Notations

IPv6 supports 128-bit address space and can potentially support 2128 or 3.4W1038 unique IP addresses (as opposed to 32-bit address space of IPv4). With this large address-space scheme, IPv6 has the capability to provide unique addresses to each and every device or node attached to the Internet.

Types of IPv6 Addresses IPv6 addresses are broadly classified into three categories:

• Unicast addresses A Unicast address acts as an identifier for a single interface. An IPv6 packet sent to a Unicast address is delivered to the interface identified by that address.

  IPv6 includes two different unicast address assignments:

  1. Global unicast address

     The global unicast address is globally unique in the Internet.

     Transitional Global Unicast Addresses

     For transition purposes, the IPv6 protocol includes the ability to embed an IPv4 address within an IPv6 address. This type of IPv4 address facilitates the tunneling of IPv6 packets over existing IPv4 networks. One example of a transitional global unicast address is the 6to4 address.

  2. Link-local address

     The link-local unicast address can be used only on the local network link. Link-local addresses are neither valid nor recognized outside the enterprise.

     * A link-local prefix has the following format:
     fe80::interface-ID/10

     *The following is an example of a link-local address:

     fe80::23a1:b152

     fe80-Hexadecimal representation of the 10-bit binary prefix 1111111010. This prefix identifies the type of IPv6 address as link local.

     interface-ID-Hexadecimal address of the interface, which is usually derived from the 48-bit MAC address.

  The type of unicast address is determined by the leftmost (high order) contiguous bits in the address, which contain the prefix.

  The unicast address format is organized in the following hierarchy:

  • Public topology

    The site prefix defines the public topology of your network to a router. You obtain the site prefix for your enterprise from an ISP or Regional Internet Registry (RIR).

  • Site (private) topology

    The subnet prefix defines the site topology to a router by specifying the specific link to which the subnet has been assigned. However, IPv6 subnet IDs are expressed in hexadecimal notation, rather than in dotted decimal notation.

  • Interface ID

    The interface ID identifies an interface of a particular node. It must be unique within the subnet. IPv6 hosts can use the Neighbor Discovery protocol to automatically generate their own interface IDs. Neighbor Discovery automatically generates the interface ID, based on the MAC or EUI-64 address of the host's interface. You can also manually assign interface IDs, which is recommended for IPv6 routers and IPv6-enabled servers.

• Multicast addresses A Multicast address acts as an identifier for a group/set of interfaces that may belong to the different nodes. An IPv6 packet delivered to a Multicast address is delivered to the multiple interfaces.
• Anycast addresses Anycast addresses act as identifiers for a set of interfaces that may belong to the different nodes. An IPv6 packet destined for an Anycast address is delivered to one of the interfaces identified by the address.

IPv6 Address Notation

IPv6 addresses are denoted by eight groups of hexadecimal quartets separated by colons in between them.

Following is an example of a valid IPv6 address:
2001:cdba:0000:0000:0000:0000:3257:9652

Any four-digit group of zeroes within an IPv6 address may be reduced to a single zero or altogether omitted. Therefore, the following IPv6 addresses are similar and equally valid:

• 2001:cdba:0000:0000:0000:0000:3257:9652
• 2001:cdba:0:0:0:0:3257:9652
• 2001:cdba::3257:9652

• ::/96 The zero prefix denotes addresses that are compatible with the previously used IPv4 protocol.
• ::/128 An IPv6 address with all zeroes in it is referred to as an unspecified address and is used for addressing purposes within a software.
• ::1/128 This is called the loop back address and is used to refer to the local host. An application sending a packet to this address will get the packet back after it is looped back by the IPv6 stack. The local host address in the IPv4 was 127.0.0.1 .
• 2001:db8::/32 This is a documentation prefix allowed in the IPv6. All the examples of IPv6 addresses should ideally use this prefix to indicate that it is an example.
• fec0::/10 This is a site-local prefix offered by IPv6. This address prefix signifies that the address is valid only within the local organization. Subsequently, the usage of this prefix has been discouraged by the RFC.
• fc00::/7 This is called the Unique Local Address (ULA). These addresses are routed only within a set of cooperating sites. These were introduced in the IPv6 to replace the site-local addresses. These addresses also provide a 40-bit pseudorandom number that reduces the risk of address conflicts.
• ff00::/8 This prefix is offered by IPv6 to denote the multicast addresses. Any address carrying this prefix is automatically understood to be a multicast address.
• fe80::/10 This is a link-local prefix offered by IPv6. This address prefix signifies that the address is valid only in the local physical link.