Qtech QSW-3900-24-Т-DC [170/313] Multicast address mapping

Qtech QSW-3900-24-Т-DC [170/313] Multicast address mapping
QTECH Software Configuration Manual
12-169
12.2.2 Multicast Address Mapping
Note:
As for link-layer multicast, this document focuses on the multicast implementations of the
Ethernet protocol only, and the multicast implementations of other link-layer protocols are
out of the scope of this document.
IANA assigned MAC addresses 01:00:5E:00:00:00 to 01:00:5E:7F:FF:FF for multicast. This requires the
28-bit IP multicast address space to be mapped to the 23-bit multicast MAC address space. To be specific, the
low-order 23 bits of the IP multicast address space are mapped to the low-order 23 bits of the multicast MAC address
space, as shown in Figure 3.
Figure 3 IP-to-MAC address mapping
As a result of this mapping, 32 multicast addresses are mapped to the same MAC address.
12.2.3 Group Membership Management
Group membership management means the establishment and maintenance of multicast group memberships
on a multicast router or switch for the subnets directly connected to it, namely, the management of multicast group
members attached to the interfaces or ports of the multicast device.
12.2.3.1 IGMP
The Internet Group Management Protocol (IGMP) runs between IP hosts and the immediately connected
router. IGMP functions in both directions: A host informs the router of its interest in specific multicast groups through
IGMP, and a multicast router uses IGMP to periodically query group memberships on the local subnet to collect and
maintain the group memberships. Through IGMP, a router learns whether a specific multicast group has active
members on the local subnet, rather than the interrelationships between a multicast group and a host.
So far, there are three IGMP versions:
IGMPv1 (documented in RFC 1112) defines the group member query and
report processes;
IGMPv2 (documented in RFC 2236) adds a leave-group mechanism based on
IGMPv1;

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