IPV6 RFC 4291 PDF

Google Network Working Group R. Please refer to the current edition of the "Internet Official Protocol Standards" STD 1 for the standardization state and status of this protocol. Distribution of this memo is unlimited. IPv6 Addressing

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Please refer to the current edition of the "Internet Official Protocol Standards" STD 1 for the standardization state and status of this protocol. Distribution of this memo is unlimited. IPv6 Addressing Addressing Model Text Representation of Addresses Text Representation of Address Prefixes Address Type Identification Unicast Addresses Interface Identifiers The Unspecified Address The Loopback Address Global Unicast Addresses Anycast Addresses Required Anycast Address Multicast Addresses Pre-Defined Multicast Addresses Security Considerations IANA Considerations Normative References Informative References Introduction This specification defines the addressing architecture of the IP Version 6 protocol.

It includes the basic formats for the various types of IPv6 addresses unicast, anycast, and multicast. There are three types of addresses: Unicast: An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address. Multicast: An identifier for a set of interfaces typically belonging to different nodes. A packet sent to a multicast address is delivered to all interfaces identified by that address.

There are no broadcast addresses in IPv6, their function being superseded by multicast addresses. In this document, fields in addresses are given a specific name, for example, "subnet". When this name is used with the term "ID" for identifier after the name e.

When it is used with the term "prefix" e. In IPv6, all zeros and all ones are legal values for any field, unless specifically excluded. Specifically, prefixes may contain, or end with, zero-valued fields. Addressing Model IPv6 addresses of all types are assigned to interfaces, not nodes.

An IPv6 unicast address refers to a single interface. All interfaces are required to have at least one Link-Local unicast address see Section 2. A single interface may also have multiple IPv6 addresses of any type unicast, anycast, and multicast or scope. Unicast addresses with a scope greater than link-scope are not needed for interfaces that are not used as the origin or destination of any IPv6 packets to or from non-neighbors. This is sometimes convenient for point-to-point interfaces.

There is one exception to this addressing model: A unicast address or a set of unicast addresses may be assigned to multiple physical interfaces if the implementation treats the multiple physical interfaces as one interface when presenting it to the internet layer. This is useful for load-sharing over multiple physical interfaces.

Multiple subnet prefixes may be assigned to the same link. Text Representation of Addresses There are three conventional forms for representing IPv6 addresses as text strings: 1. Due to some methods of allocating certain styles of IPv6 addresses, it will be common for addresses to contain long strings of zero bits. In order to make writing addresses containing zero bits easier, a special syntax is available to compress the zeros.

The use of "::" indicates one or more groups of 16 bits of zeros. The "::" can only appear once in an address. The "::" can also be used to compress leading or trailing zeros in an address. For example, the following addresses DBCA a unicast address FF a multicast address the loopback address the unspecified address may be represented as DBCA a unicast address FF a multicast address the loopback address :: the unspecified address 3. An alternative form that is sometimes more convenient when dealing with a mixed environment of IPv4 and IPv6 nodes is x:x:x:x:x:x:d.

Examples: Address Type Identification The type of an IPv6 address is identified by the high-order bits of the address, as follows: Address type Binary prefix IPv6 notation Section Unspecified The general format of Global Unicast addresses is described in Section 2.

Future specifications may redefine one or more sub-ranges of the Global Unicast space for other purposes, but unless and until that happens, implementations must treat all addresses that do not start with any of the above-listed prefixes as Global Unicast addresses.

There are several types of unicast addresses in IPv6, in particular, Global Unicast, site-local unicast deprecated, see Section 2. Additional address types or subtypes can be defined in the future. The known boundaries will differ from router to router, depending on what positions the router holds in the routing hierarchy.

Except for the knowledge of the subnet boundary discussed in the previous paragraphs, nodes should not make any assumptions about the structure of an IPv6 address. Interface Identifiers Interface identifiers in IPv6 unicast addresses are used to identify interfaces on a link. They are required to be unique within a subnet prefix. It is recommended that the same interface identifier not be assigned to different nodes on a link. They may also be unique over a broader scope.

The same interface identifier may be used on multiple interfaces on a single node, as long as they are attached to different subnets. Note that the uniqueness of interface identifiers is independent of the uniqueness of IPv6 addresses. For example, a Global Unicast address may be created with a local scope interface identifier and a Link-Local address may be created with a universal scope interface identifier. Modified EUI format-based interface identifiers may have universal scope when derived from a universal token e.

In the resulting Modified EUI format, the "u" bit is set to one 1 to indicate universal scope, and it is set to zero 0 to indicate local scope. The motivation for inverting the "u" bit when forming an interface identifier is to make it easy for system administrators to hand configure non-global identifiers when hardware tokens are not available. This is expected to be the case for serial links and tunnel end-points, for example.

The alternative would have been for these to be of the form , , etc. IPv6 nodes are not required to validate that interface identifiers created with modified EUI tokens with the "u" bit set to universal are unique. The Unspecified Address The address is called the unspecified address. It must never be assigned to any node. It indicates the absence of an address. One example of its use is in the Source Address field of any IPv6 packets sent by an initializing host before it has learned its own address.

The unspecified address must not be used as the destination address of IPv6 packets or in IPv6 Routing headers. An IPv6 packet with a source address of unspecified must never be forwarded by an IPv6 router. The Loopback Address The unicast address is called the loopback address. It may be used by a node to send an IPv6 packet to itself. It must not be assigned to any physical interface. It is treated as having Link-Local scope, and may be thought of as the Link-Local unicast address of a virtual interface typically called the "loopback interface" to an imaginary link that goes nowhere.

The loopback address must not be used as the source address in IPv6 packets that are sent outside of a single node. An IPv6 packet with a destination address of loopback must never be sent outside of a single node and must never be forwarded by an IPv6 router.

A packet received on an interface with a destination address of loopback must be dropped. Global Unicast addresses that start with binary have no such constraint on the size or structure of the interface ID field. Examples of Global Unicast addresses that start with binary are the IPv6 address with embedded IPv4 addresses described in Section 2. An example of global addresses starting with a binary value other than and therefore having a bit interface ID field can be found in [ GLOBAL ].

New or updated implementations are not required to support this address type. This address type is used to represent the addresses of IPv4 nodes as IPv6 addresses. Routers must not forward any packets with Link-Local source or destination addresses to other links. Site-Local IPv6 Unicast Addresses Site-Local addresses were originally designed to be used for addressing inside of a site without the need for a global prefix.

Existing implementations and deployments may continue to use this prefix. Anycast addresses are allocated from the unicast address space, using any of the defined unicast address formats. Thus, anycast addresses are syntactically indistinguishable from unicast addresses. 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 know that it is an anycast address.

For any assigned anycast address, there is a longest prefix P of that address that identifies the topological region in which all interfaces belonging to that anycast address reside. Within the region identified by P, the anycast address must be maintained as a separate entry in the routing system commonly referred to as a "host route" ; outside the region identified by P, the anycast address may be aggregated into the routing entry for prefix P.

Note that in the worst case, the prefix P of an anycast set may be the null prefix, i. In that case, the anycast address must be maintained as a separate routing entry throughout the entire Internet, which presents a severe scaling limit on how many such "global" anycast sets may be supported.

Therefore, it is expected that support for global anycast sets may be unavailable or very restricted.

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RFC Errata

Date Rejected: Section 2. Due to some methods of allocating certain styles of IPv6 addresses, it will be common for addresses to contain long strings of zero bits. In order to make writing addresses containing zero bits easier, a special syntax is available to compress the zeros. The use of "::" indicates one or more groups of 16 bits of zeros. The "::" can only appear once in an address. The "::" can also be used to compress leading or trailing zeros in an address. For example, the following addresses DBCA a unicast address FF a multicast address the loopback address the unspecified address may be represented as DBCA a unicast address FF a multicast address the loopback address :: the unspecified address It should say: 2.

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Introduction 1. It includes the basic formats for the various types of IPv6 addresses unicast, anycast, and multicast. IPv6 Addressing 2. A packet sent to a unicast address is delivered to the interface identified by that address. A packet sent to a multicast address is delivered to all interfaces identified by that address. When this name is used with the term "ID" for identifier after the name e. When it is used with the term "prefix" e.

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