IPv6 Addresses
Scope of IPv6 Addresses

Another new concept of IPv6 is the scope of addresses. This concept defines the network topology in which the address is unique. It essentially replaces TTL. RFC 4007 defines the scope of addresses.

Available scopes depend on the type of addresses. Multicast addresses have the finest classification of scope. There are the following levels:

There are two levels for Global Unicast and Anycast addresses:

The zone concept is closely related to the scope of addresses. The Zone defines the part of network that corresponds to the scope of the address in which the address is unique. The boundaries of zones pass through devices, not link, and the whole zone is always included in the superior zone of greater scope. Zones of the same scope cannot overlap each other and are either identical or mutually separated. The zone must be continuous with regard to the forwarding; otherwise the datagram would be able to leave the zone during its transfer.

Example of IPv6 Addresses Scope

The individual zones are necessary to distinguish on the device. For this purpose, the Zone Index was introduced. It consists of Scope Zone that is derived from its own address whose notation is address%zone, and Sequence Number. The individual Zone Indices are assigned to each device internally and are not mutually synchronized with its neighbors within the same zone. The Zone Indices are typically used to identify zones in the routing tables within a single device.

The entry of IPv6 address with Zone Index FF02::1%1 can be an example. It is the multicast address for all nodes on the link.

RFC 4007 also provides the implicitly zone (value 0) that is inserted if the address does not contain Zone Index. The Global Unicast addresses for which there is only one zone can be an example. However, this zone is not explicitly noted.