The most significant change from IPv4 to IPv6 is the length of network addresses. IPv6 addresses are 128 bits long vs. 32 bits in IPv4. The number of possible addresses in IPv6 is about 3.4 x 1038.
The format of IPv6 address
In many situations, IPv6 addresses are composed of two logical parts: a 64-bit network prefix, and a 64-bit host-addressing part, which is often automatically generated from the interface MAC address. IPv6 address consists of 8 groups of 16-bit hexadecimal values separated by colons (:) shown as follows:
The format of IPv6 address is:
| 16 bits | 16 bits | 16 bits | 16 bits | 16 bits | 16 bits | 16 bits | 16 bits |
aaaa : aaaa : aaaa : aaaa : aaaa : aaaa : aaaa : aaaa
Three types of IPv6 addresses:
IPv6 address is classified in three types: Unicast, Multicast and Anycast. Unicast Address is applied to one network interface.
The common global unicast address divisions:
| Global Routing Prefix (N bits) | Subnet ID (64-N bits) | Interface ID (64 bits) |
Link-local unicast address divisions:
| 1111111010 (10 bits) | 0x00…0 (54bits) | Interface ID (64 bits) |
Site-local unicast address divisions:
| 1111111011 (10 bits) | 0x00…0 | SLA | Interface ID (64 bits) |
(Interface ID is based on hardware MAC address.)
Multicast Address: applied for multiple network interfaces, and communication is conducted with all hosts with the same address.
| 0xFF (8 bits) | Flag (4bits) | Scope(4bits) | Group ID (64 bits) |
The first octet of ones identifies the address as a multicast address. The flags field identifies whether the multicast address is a well-known address or a transient multicast address. The scope field identifies the scope of the multicast address. The 112-bit group ID identifies the multicast group.
Anycast Address: applied for multiple network interfaces, but actual communication is conducted with one of them. It has the same format as the Unicast. Similar to multicast addresses, anycast addresses identify a set of interfaces. However, packets are sent to only one of the interfaces, not to all interfaces. Anycast addresses are allocated from the normal unicast address space and cannot be distinguished from a unicast address in format. Therefore, each member of an anycast group must be configured to recognize certain addresses as anycast addresses.
There are no broadcast addresses in IPv6, their function being superseded by multicast addresses. Broadcast in IPv6 is a special form of Multicast.
IPv4 mapped to IPv6 address:
| 0x00…0 (80 bits) | 0xFFFF (16 bits) | IPv4 Address (32 bits) |
IPv4-competible IPv6 address:
| 0x00…0 (80 bits) | 0x0000 (16 bits) | IPv4 Address (32 bits) |
IPv6 Address Scope
IPv6 addresses have scope, which identifies the application suitable for the address. Unicast and multicast addresses support scoping.
Unicast addresses support two types of scope: globalscope and localscope. There are two types of local scope: link-localaddresses and site-localaddresses. Link-local unicast addresses are used within a single network link. The first 10 bits of the prefix identify the address as a link-local address. Link-local addresses cannot be used outside a network link. Site-local unicast addresses are used within a site or intranet. A site consists of multiple network links, and site-local addresses identify nodes inside the intranet. Site-local addresses cannot be used outside the site.
Multicast addresses support 16 different types of scope, including node, link, site,organization, and global scope. A four-bit field in the prefix identifies the scope.
IPv6 Address allocation and Management
IP address is a public resource without any organization or individual ownership. Address management is conducted in a hierarchical manner, and the top of this hierarchy is IANA (Internet Assigned Numbers Authority). IANA allocates addresses to Regional Internet Registry, or RIR. Currently, there are four RIR: APNIC (Asia Pacific Network Information Centre), ARIN for North America, RIPE NCC (Reseaux IP Europeans Network Coordination Centre) mainly for Europe, and LACNIC (Latin American and Caribbean Internet Addresses Registry) for South America and Caribbean regions.
RIR (or NIR) allocates address to organizations called LIR (Local Internet Registry). An LIR is an organization which is delegated by RIR or NIR to allocate address to users. LIR usually is a service provider. An LIR allocates acquired address to end user organizations, or other ISPs.
RIR (NIR) does not assign global IPv6 address directly to an end user organization, in order to maximize route optimization. Any end user organization gets global IPv6 addresses assigned by the service provider they connect to. If the organization changes the service provider, global routing prefix is inevitably changed.
IP Address Management Hierarchy
Related Terms: IPv4, IPv6, Anycast, Unicast, Multicast, Broadcast, IARA, RIR, LIR