July 2002
Beginner
360 pages
11h 19m
English
Content preview from IPv6 Essentials
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Multicast Address
A multicast address is an identifier
for a group of nodes, identified by the high-order byte
FF, or 1111 1111 in
binary
notation (refer to Table 3-2). A node can belong
to more than one multicast group. Multicast exists in IPv4, but it
has been redefined and improved for IPv6. The multicast address
format is shown in Figure 3-9.
Figure 3-9. Format of the multicast address
The first byte identifies the address as a multicast address. The next 4 bits are used for Flags, defined as follows: The first 3 bits of the Flag field must be zero; they are reserved for future use. The last bit of the Flag field indicates whether this address is permanently assigned—i.e., one of the well-known multicast addresses assigned by the IANA—or a temporary multicast address. A value of zero for the last bit defines a well-known address; a value of one indicates a temporary address. The Scope field is used to limit the scope of a multicast address. The possible values are shown in Table 3-5.
Table 3-5. Values for the Scope field
|
Value |
Description |
|---|---|
|
0 |
Reserved |
|
1 |
Node-local scope (name changed to interface-local in new draft) |
|
2 |
Link-local scope |
|
3, 4 |
Unassigned |
|
5 |
Site-local scope |
|
6, 7 |
Unassigned |
|
8 |
Organization-local scope |
|
9, A, B, C, D |
Unassigned |
|
E |
Global scope |
|
F |
Reserved |
Well-Known Multicast Addresses
The last 112 bits of the address carry the multicast group ...
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