segments. Each segment is written in hexadecimal between 0x000 and 0xFFF, separated by colons. The hexadecimal digits A, B, C, D, E, and F represented in IPv6 are not case sensitive. IPv6 does not require explicit address string notation. Use the following guidelines for IPv6 address string notations: Using the “::” notation greatly reduces the size of most addresses. For example, FF01:0:0:0:0:0:0:1 becomes FF01::1. Note
An address parser identifies the number of missing zeros by separating the two parts and entering 0 until the 128 bits are complete. If two “::” notations are placed in the address, there is no way to identify the size of each block of zeros.
Content 8.2 IPv6 Addressing 8.2.5 IPv6 Address Types The IPv6 addressing structure is defined in multiple RFCs, including RFC 3513 and the new RFC 4291 (obsoletes RFC 3513). Each RFC defines three types of IPv6 addresses: Unicast Address
A unicast address identifies a single device. A packet sent to a unicast address is delivered to the interface identified by that address. There are two types of unicast addresses: All interfaces are required to have at least one link-local unicast address. However, a fundamental feature of IPv6 is that a single interface may also have multiple IPv6 addresses of any type (unicast, anycast, and multicast). Note
There is also a site-local unicast address; however, the IETF is currently working on removing or replacing site-local addresses. Therefore, this module does not include this address type. Multicast Address
IPv6 does not have broadcast addresses. Broadcasting in IPv4 results in several problems: It generates a number of interrupts in every computer on the network and, in some cases, triggers malfunctions that can completely halt an entire network. This disastrous network event is called a “broadcast storm.” Broadcasts are replaced by multicast addresses. Multicast enables efficient network operation by using functionally specific multicast groups to send requests to a limited number of computers on the network. A packet sent to a multicast address is delivered to all interfaces identified by that address. The range of multicast addresses in IPv6 is larger than in IPv4. For the foreseeable future, allocation of multicast groups is not being limited. Anycast Address
IPv6 also defines a new type of address called anycast. An anycast address identifies a list of devices or nodes; therefore, an anycast address identifies multiple interfaces. A packet sent to an anycast address is delivered to the closest interface, as defined by the routing protocols in use. Anycast addresses are syntactically indistinguishable from global unicast addresses, because anycast addresses are allocated from the global unicast address space. Note
Anycast addresses cannot be used as the source address of an IPv6 packet. Special addresses
There are a number of addresses with special meaning in IPv6. Some of these are presented in Figure .
Web Links RFC 3513 - Internet Protocol Version 6 (IPv6) Addressing Architecture
ftp://ftp.rfc-editor.org/in-notes/rfc3513.txt RFC 4291 - IP Version 6 Addressing Architecture
ftp://ftp.rfc-editor.org/in-notes/rfc4291.txt
Content 8.2 IPv6 Addressing 8.2.6 IPv6 Global Unicast and Anycast Addresses Global unicast and anycast addresses share the same format. The unicast address space allocates the anycast addresses. These addresses appear as unicast addresses to devices that are not configured for anycast. When a unicast address is assigned to more than one interface, thus turning it into an anycast address, the nodes to which the address is assigned must be explicitly configured to use and recognize the anycast address. A packet that is sent to an anycast address routes to the closest device or interface that shares the address. A sender creates a packet with the anycast as the destination address and forwards it to its nearest router. The source can use anycast addresses to control the pathway across which traffic flows. An example of anycast use in a Border Gateway Protocol (BGP) multihomed network is when a customer has multiple ISPs with multiple connections to one another. The customer can configure a different anycast address for each ISP. Each router for the given ISP has the same configured anycast address. The source device can choose which ISP to send the packet to. However, the routers along the path determine the closest router to reach that ISP using the IPv6 anycast address. Another use for an anycast is when a LAN is attached to multiple routers. These routers can have the same IPv6 anycast address so that distant devices need to identify only the anycast address. Intermediate devices can choose the best pathway to reach the closest entry point to that subnet. The IPv6 global unicast address is the equivalent of the IPv4 global unicast address. The address structure enables routing prefixes to be aggregated, thereby limiting the number of routing table entries in the global routing table. Global unicast addresses used on links are aggregated upward through organizations and eventually to the ISPs. Global unicast addresses are defined by a global routing prefix, a subnet ID, and an interface ID. The IPv6 unicast address space encompasses the entire IPv6 address range, with the exception of FF00::/8 (1111 1111), which is used for multicast addresses. The current global unicast address assignment by the Internet Assigned Numbers Authority (IANA) uses the range of addresses that start with binary value 001 (2000::/3), which is one-eighth of the total IPv6 address space and is the largest block of assigned block addresses. Addresses with a prefix of 2000::/3 (001) through E000::/3 (111), with the exception of the FF00::/8 (1111 1111) multicast addresses, are required to have 64-bit interface identifiers in the extended universal identifier (EUI)-64 format. The global unicast address typically consists of a 48-bit global routing prefix and a 16-bit subnet ID. In the now obsolete RFC 2374, IPv6 Aggregatable Global Unicast Address Format, the global routing prefix included two other hierarchically structured fields called Top Level Aggregator and Next-Level Aggregator. Because these fields were policy-based, the IETF decided to remove them from the RFCs. However, some existing IPv6 networks deployed in the early days might still be using networks based on the older architecture. A 16-bit subnet field called Subnet ID could be used by individual organizations to create their own local addressing hierarchy and to identify subnets. This field allows