HP 6125XLG R2306-HP 6125XLG Blade Switch IP Multicast Configuration Guide - Page 15

Ethernet multicast MAC addresses, Scope, Value, Meaning, Group ID

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{ Scope-The Scope field contains four bits, which indicate the scope of the IPv6 internetwork for which the multicast traffic is intended. Table 5 Values of the Scope field Value 0, F 1 2 3 4 5 6, 7, 9 through D 8 E Meaning Reserved. Interface-local scope. Link-local scope. Subnet-local scope. Admin-local scope. Site-local scope. Unassigned. Organization-local scope. Global scope. { Group ID-The Group ID field contains 112 bits. It uniquely identifies an IPv6 multicast group in the scope that the Scope field defines. Ethernet multicast MAC addresses • IPv4 multicast MAC addresses: As defined by IANA, the most significant 24 bits of an IPv4 multicast MAC address are 0x01005E. Bit 25 is 0, and the other 23 bits are the least significant 23 bits of a multicast IPv4 address. Figure 6 IPv4-to-MAC address mapping The most significant four bits of a multicast IPv4 address are 1110. Only 23 bits of the remaining 28 bits are mapped to a MAC address, so five bits of the multicast IPv4 address are lost. As a result, 32 multicast IPv4 addresses map to the same IPv4 multicast MAC address. Therefore, a device might receive some unwanted multicast data at Layer 2 processing, which needs to be filtered by the upper layer. • IPv6 multicast MAC addresses: As defined by IANA, the most significant 16 bits of an IPv6 multicast MAC address are 0x3333 as its address prefix. The least significant 32 bits are the least significant 32 bits of a multicast IPv6 address and are mapped to the remaining IPv6 multicast MAC address, so the problem of duplicate IPv6-to-MAC address mapping also arises like IPv4-to-MAC address mapping. 8

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8
{
Scope
—The Scope field contains four bits, which indicate the scope of the IPv6 internetwork for
which the multicast traffic is intended.
Table 5
Values of the Scope field
Value
Meaning
0, F
Reserved.
1
Interface-local scope.
2
Link-local scope.
3
Subnet-local scope.
4
Admin-local scope.
5
Site-local scope.
6, 7, 9 through D
Unassigned.
8
Organization-local scope.
E
Global scope.
{
Group ID
—The Group ID field contains 112 bits. It uniquely identifies an IPv6 multicast group in
the scope that the Scope field defines.
Ethernet multicast MAC addresses
•
IPv4 multicast MAC addresses:
As defined by IANA, the most significant 24 bits of an IPv4 multicast MAC address are 0x01005E.
Bit 25 is 0, and the other 23 bits are the least significant 23 bits of a multicast IPv4 address.
Figure 6
IPv4-to-MAC address mapping
The most significant four bits of a multicast IPv4 address are 1110. Only 23 bits of the remaining
28 bits are mapped to a MAC address, so five bits of the multicast IPv4 address are lost. As a result,
32 multicast IPv4 addresses map to the same IPv4 multicast MAC address. Therefore, a device
might receive some unwanted multicast data at Layer 2 processing, which needs to be filtered by
the upper layer.
•
IPv6 multicast MAC addresses:
As defined by IANA, the most significant 16 bits of an IPv6 multicast MAC address are 0x3333
as its address prefix. The least significant 32 bits are the least significant 32 bits of a multicast IPv6
address and are mapped to the remaining IPv6 multicast MAC address, so the problem of
duplicate IPv6-to-MAC address mapping also arises like IPv4-to-MAC address mapping.