TCP/IP Tutorial and Technical Overview - IBM Redbooks

Subnet ID An identifier of a subnet within the site.The subnet field is
designed to be structured hierarchically by site
administrators.
Interface ID Interface identifiers in IPv6 unicast addresses are used to
identify interfaces on a link. They are required to be
unique within a subnet prefix. Do not assign the same
interface identifier to different nodes on a link. They can
also be unique over a broader scope. In some cases, an
interface's identifier will be derived directly from that
interface's link layer address. The same interface
identifier can be used on multiple interfaces on a single
node as long as they are attached to different subnets.
All unicast addresses, except those that start with binary value 000, have
interface IDs that are 64 bits long and constructed in Modified EUI-64 format.
Multicast address
A multicast address is an identifier assigned to a set of interfaces on multiple
hosts. Packets sent to that address will be delivered to all interfaces
corresponding to that address. (See 3.3, “Internet Group Management Protocol
(IGMP)” on page 119 for more information about IP multicasting.) There are no
broadcast addresses in IPv6, their function being superseded by multicast
addresses. Figure 9-9 shows the format of an IPv6 multicast address.
Figure 9-9 IPv6 multicast address format
Where:
0 8 12 16 127
FP Flags Scope
Group ID
FP Format Prefix: 1111 1111.
Flags Set of four flag bits. Only the low order bit currently has
any meaning, as follows:
0000 Permanent address assigned by a numbering
authority.
0001 Transient address. Addresses of this kind can
be established by applications as required.
When the application ends, the address will be
released by the application and can be reused.
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