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24 Description of IGMP Snooping and MLD Snooping
is received from any port, the entry itself is deleted.
If the Switch does not receive an IGMP Report (membership request) message
within 260 seconds, it deletes the corresponding entries.
(2) Layer 2 forwarding for IPv4 multicast packet
Layer 2 forwarding within VLANs receiving IPv4 multicast packets is performed based on
MAC address. Layer 2 forwarding is performed based on IGMP snooping results for all
ports that receive IGMP Report (membership request) messages with IP multicast
addresses that are mapped to the same MAC address.
Because the multicast MAC address for both 224.10.10.10 and 225.10.10.10 as shown in
the example for (a) Registering entries in (1) MAC address learning is 0100.5E0A.0A0A,
when Layer 2 forwarding is performed for multicast data bound for 224.10.10.10, that
multicast data is also forwarded to the ports receiving IGMP Report (membership request)
messages bound for 225.10.10.10.
24.3.2 Connections with multicast routers
In addition to the hosts that have already joined a group, the forwarding destinations for
multicast packets also include neighboring multicast routers. When the Switch and a
multicast router are connected and IGMP snooping is used, the port connected to the
multicast router to forward multicast packets to the router (abbreviated hereafter to
multicast router port) can be specified by configuration.
The Switch forwards all multicast packets to the specified multicast router port.
Also, because IGMP is a protocol for sending and reception between router hosts, IGMP
messages are accepted by routers and hosts. The Switch forwards IGMP messages as
shown in the following table.
Table 24-3 Operation for IGMP messages
IGMP message type
Membership Query
Version 2 Membership
Report
Leave Group
Version 1 Membership
Report
#
This is the forwarding operation when a querier is set for the local device. If no
querier has been set, forwarding is always performed to multicast router ports.
However, if a port that has not received an IGMP Report (membership request)
message receives an IGMP Leave message, the IGMP Leave message is not
forwarded regardless of the querier settings.
24.3.3 IGMP querier functionality
The IGMP querier functionality is used by the Switch to send IGMP Query messages by
proxy to recipient hosts on environments where no multicast router exists in the VLAN, and
only hosts that send and receive multicast packets exist. Multicast routers regularly send
IGMP Query messages and then check for reception from hosts to determine whether
group members exist. If no multicast router exists, group members can no longer be
438
Transfer port within the VLAN
Forwarded to all ports.
Forwarded only to multicast router ports.
Not forwarded to any port when group members still exist for other
ports.
Forwarded to multicast router ports when no group members exist
for other ports.
Forwarded only to multicast router ports.
Rem
arks
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