АМАТЕК AN-SGM28P24-400 [215/322] Second layer dynamic multicast

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and the network bandwidth is saved。

Multicast group includes multicast group address, member port, VLAN ID, Age time。

The formation of MLD SNOOPING multicast group is a learning process. When one port of

the switch receives the MLD REPORT packet, MLD SNOOPING generates a new multicast

group, and the port that receives the MLD REPORT packet is added to the multicast group. When

a MLD QUERY packet is received by the switch, if the multicast group already exists in the

switch, then the port received the MLD QUERY is added to the multicast group, otherwise it will

only forward the MLD QUERY packet. Done SNOOPING also supports the MLD mechanism of

MLD V2 MLD SNOOPING; if the configuration of the fast-leave ENABLE in MLD V2, received

Done packet when it receives port can leave the multicast group immediately; if the configuration

of the fast-leave left the waiting time (fast-leave-timeout), then the multicast group waiting for this

time expires after leaving the multicast group。

There are two update mechanisms for MLD SNOOPING. One is the Done mechanism

described above. In most cases, MLD SNOOPING deletes expired multicast groups through age

time. When the multicast group joins the MLD SNOOPING, the added time is recorded. When the

multicast group has more than one configured age time in the switch, the exchange opportunity

deletes the multicast group。

When a port to receive Done packets, this port will immediately removed from the multicast

group to which it belongs, this situation may affect the continuity of the network data stream;

because this network equipment port below may be connected to a HUB or no MLD SNOOPING

function, the equipment connected to receive the multicast data under many of the current

equipment. A device sends Done, which may affect other devices and can not receive multicast

data streams. Fast-leave-timeout mechanism can prevent the occurrence of this situation, through

the Fast-leave-timeout configuration of a left waiting time, port leave packets received after

waiting for Fast-leave-timeout long time and then removed from the multicast group to which it

belongs, to guarantee the continuity of network multicast stream。

16.1.2 Second layer dynamic multicast

The multicast MAC address entries in the two layer hardware multicast forwarding table can

be dynamically learned by MLD SNOOPING. The IPV6 multicast MAC address is dynamically

learned through MLD SNOOPING。

When the switch off MLD SNOOPING, the two layer hardware multicast forwarding table in

unregistered forwarding mode, multicast MAC address cannot be dynamically learned that two

layer hardware multicast forwarding table no entries, two layer multicast data stream as all