Igmp Multicast Vlan - D-Link DES-3526 - Switch - Stackable User Manual

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xStack DES-3500 Series Layer 2 Stackable Fast Ethernet Managed Switch User Manual

IGMP Multicast VLAN

Standard Internet Group Management Protocol (IGMP) snooping purposely limits multicast traffic so that only the interfaces
actively associating with the multicast are flooded. A layer 2 switch will snoop IGMP packet traffic between a multicast router
and host devices to learn and record the associated multicast groups and their member ports. A multicast forwarding table is
maintained for each multicast group. The table consists of entries that match the multicast group with ports used for the multicast.
A host will send an IGMP Join Group and Leave Group request when it wishes to receive or terminate a particular IP multicast.
The Switch also sends periodic queries to multicast routers for membership reports used to keep the multicast group tables up to
date.
IGMP snooping works well for enterprise or even campus level implementations using adequate and well-placed switching
capacity. However, IGMP snooping is problematic for service providers that wish to deploy subscriber-based multicast traffic in
an Ethernet switching environment when subscriber ports have their own unique VLAN; and because of the nature of the
communication between an IGMP snooping enabled switch and the multicast router. This creates a problem for sending multicasts
across separate VLANs.
The DES-3526 addresses this need by allowing the Switch to create a special network-wide shared VLANs used for multicasting.
This allows each port to be in separate VLANs while using the special VLAN for multicast streams. A subscriber may subscribe
(Join Group) or unsubscribe (Leave Group) to a multicast while the remaining subscribers are isolated from the multicast.
The Switch uses the special multicast VLAN to qualify MAC addresses in the Switch forwarding table as being members of the
multicast. It uses IGMP to modify the forwarding table, that is, to add or delete MAC addresses as it receives Join or Leave
requests from host devices.
To create IGMP Multicast VLANs for the Switch, click Configuration > IGMP > IGMP Multicast VLAN, which will display
the following window for the user to configure.
Figure 6- 20 Multicast VLAN and Current Multicast VLANs Entries Table
To create a new Multicast VLAN, click the Add button in the window above. The following window will be displayed.
Figure 6- 21 Multicast VLAN window - Add
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