IP Version 6 Addressing Architecture
obsoleted by
- rfc-3513 — Internet Protocol Version 6 (IPv6) Addressing Architecture
obsoletes
- rfc-1884 — IP Version 6 Addressing Architecture
Extracted elements (28)
New IPv6 multicast addresses should place the group identifier in the low-order 32 bits so that the mapping to IEEE 802 MAC addresses (which uses the low-order 32 bits of the IPv6 multicast address) produces unique MAC addresses. Group IDs of 32 bits or less guarantee unique MAC-layer multicast addresses.
The 'u' bit is inverted when forming the interface identifier from EUI-64 to make it easy for administrators to hand-configure local-scope identifiers. Without inversion, locally-scoped IDs would need forms like 0200:0:0:1 instead of the simpler ::1, ::2, etc.
A host is required to recognize as its own: its link-local address for each interface, assigned unicast addresses, the loopback address, all-nodes multicast addresses, solicited-node multicast addresses for each unicast/anycast address, and all joined multicast group addresses.
A router is required to recognize all host addresses plus: subnet-router anycast addresses for its interfaces, all configured anycast addresses, all-routers multicast addresses, and all joined multicast group addresses.
All interfaces are required to have at least one link-local unicast address. A single interface may be assigned multiple IPv6 addresses of any type or scope.
An anycast address must not be used as the source address of an IPv6 packet, and must not be assigned to an IPv6 host — it may only be assigned to an IPv6 router.
Format prefixes 001 through 111 (except Multicast, 1111 1111) are all required to have 64-bit interface identifiers in EUI-64 format.
Multicast addresses must not be used as source addresses in IPv6 packets or appear in any routing header.
Routers must not forward any packets with link-local source or destination addresses to other links. Routers must not forward packets with site-local source or destination addresses outside of the site.
The loopback address (::1) must not be used as the source address in packets sent outside a single node, and packets destined to the loopback address must never be sent outside a node or forwarded by a router.
The unspecified address (0:0:0:0:0:0:0:0, written as '::') must never be assigned to any node and must not be used as the destination address of IPv6 packets or in IPv6 Routing Headers. It is used as a source address by initializing hosts before address assignment.
Anycast addresses are syntactically indistinguishable from unicast addresses and are allocated from the unicast address space. Nodes assigned an anycast address must be explicitly configured to know it is an anycast address.
Interface identifiers in IPv6 unicast addresses must be unique on their link and are required to be 64 bits long in EUI-64 format for many address types. The 'u' (universal/local) bit must be inverted when forming an interface identifier from an EUI-64 token: '1' means global scope, '0' means local scope.
IPv6 addresses are 128-bit identifiers for interfaces and sets of interfaces. There are three types: unicast (single interface), anycast (nearest of a set), and multicast (all of a set). There are no broadcast addresses in IPv6; multicast supersedes that function.
Pre-defined multicast addresses include: All Nodes (FF01::1, FF02::1), All Routers (FF01::2, FF02::2, FF05::2), and Solicited-Node (FF02::1:FFxx:xxxx). Reserved multicast addresses FF00:: through FF0F:: must never be assigned to any multicast group.
The address type is indicated by the leading bits (Format Prefix, FP). Aggregatable Global Unicast Addresses use prefix 001 (1/8 of address space); Link-Local Unicast uses 1111111010; Site-Local Unicast uses 1111111011; Multicast uses 11111111. Approximately 15% of address space is initially allocated.
The multicast scope field (4 bits) defines: 1=node-local, 2=link-local, 5=site-local, 8=organization-local, E=global, with 0 and F reserved. Permanently-assigned multicast addresses have scope-independent meaning; transient addresses are meaningful only within a given scope.
The '::' notation may be used to compress one or more consecutive groups of 16 zero bits in an IPv6 address text representation. The '::' may appear only once in an address.
The Solicited-Node multicast address is formed by appending the low-order 24 bits of a unicast or anycast address to the prefix FF02:0:0:0:0:1:FF00::/104. A node must compute and join the Solicited-Node multicast address for every unicast and anycast address it is assigned.
The Subnet-Router anycast address is predefined and has the format: n-bit subnet prefix followed by 128-n zero bits. All routers must support the Subnet-Router anycast addresses for the subnets on which they have interfaces.
The Format Prefix (FP) space defines the initial allocation of IPv6 address types. 15% of address space is initially allocated; the remaining 85% is reserved for future use. IANA manages assignment of new IPv6 multicast addresses per [MASGN].
IPv6 addressing documents do not have any direct impact on Internet infrastructure security. Authentication of IPv6 packets is defined in the IP Authentication Header specification [AUTH, RFC 1826].
IPv4-compatible IPv6 addresses have 80 zero bits, a 16-bit zero field, and a 32-bit IPv4 address in the low order. IPv4-mapped IPv6 addresses have 80 zero bits, 16 bits of 0xFFFF, and a 32-bit IPv4 address, used to represent IPv4-only nodes as IPv6 addresses.
IPv6 address prefixes are represented as ipv6-address/prefix-length in CIDR-like notation, where prefix-length is a decimal value specifying the number of leftmost contiguous bits comprising the prefix. Trailing zeros within a 16-bit chunk of the address must not be dropped.
Link-Local unicast addresses have a 10-bit prefix of 1111111010 (FE80::/10), followed by 54 zero bits and a 64-bit interface ID. Site-Local addresses use prefix 1111111011 (FEC0::/10), with 38 zero bits, a 16-bit subnet ID, and a 64-bit interface ID.
Multicast addresses have the format: 8-bit prefix 0xFF, 4-bit flags field (high 3 bits reserved/zero; T=0 for permanent, T=1 for transient), 4-bit scope field, and 112-bit group ID. New multicast addresses should place the group ID in the low-order 32 bits.
The preferred text representation of IPv6 addresses is x:x:x:x:x:x:x:x, eight groups of four hexadecimal digits separated by colons. Leading zeros within each 16-bit group may be omitted, but each group must have at least one digit.
To create an EUI-64 interface identifier from an IEEE 802 48-bit MAC address, insert two octets (0xFF and 0xFE) between the company_id and vendor-supplied id, then invert the universal/local bit. This is the preferred method when IEEE 802 MAC addresses are available.