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Chapter 24 Multicast
24.1.4 IGMP Snooping and VLANs
The Switch can perform IGMP snooping on up to 16 VLANs. You can configure the Switch to
automatically learn multicast group membership of any VLANs. The Switch then performs IGMP
snooping on the first 16 VLANs that send IGMP packets. This is referred to as auto mode.
Alternatively, you can specify the VLANs that IGMP snooping should be performed on. This is
referred to as fixed mode. In fixed mode the Switch does not learn multicast group membership of
any VLANs other than those explicitly added as an IGMP snooping VLAN.
24.1.5 IGMP Proxy
IGMP proxy enables a layer-2 switch to maintain a joined member list for each IGMP group on the
switch. This switch automatically and periodically sends queries to the VDSL ports to get the
subscribing information and response the upper layer router's query for the member list. In
addition, it enables the switch not to report the leave request sent from one subscriber to upper
layer router if there are still other subscriber(s) in the same IGMP group. It also allows the switch
not to report the join request sent from one subscriber to upper layer router if any subscriber is still
in the same IGMP group. In other words, an IGMP proxy switch only forward the first join request
and the last leave request in an IGMP network to its upper layer router. It can reduce multicast
traffic significantly.
Note: Note: You must set one of Gigabit Ethernet ports to "Fixed mode" before enabling
IGMP proxy.
24.1.6 Multicast Listener Discovery
The Multicast Listener Discovery (MLD) protocol (defined in RFC 2710) is derived from IPv4's
Internet Group Management Protocol version 2 (IGMPv2). MLD uses ICMPv6 message types, rather
than IGMP message types. MLDv1 is equivalent to IGMPv2 and MLDv2 is equivalent to IGMPv3.
MLD allows an IPv6 switch or router to discover the presence of MLD hosts who wish to receive
multicast packets and the IP addresses of multicast groups the hosts want to join on its network.
MLD snooping and MLD proxy are analogous to IGMP snooping and IGMP proxy in IPv4.
MLD filtering controls which multicast groups a port can join.
24.1.7 MLD Messages
A multicast router or switch periodically sends general queries to MLD hosts to update the multicast
forwarding table. When an MLD host wants to join a multicast group, it sends an MLD Report
message for that address.
An MLD Done message is equivalent to an IGMP Leave message. When an MLD host wants to leave
a multicast group, it can send a Done message to the router or switch. If the leave mode is not set
to immediate, the router or switch sends a group-specific query to the port on which the Done
message is received to determine if other devices connected to this port should remain in the
group.
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VES1724-56 User's Guide
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