3Com 5000 ATM manual Before implementing Igmp snooping

5-2CHAPTER 5: INTERNET GROUP MANAGEMENT PROTOCOL (IGMP) SNOOPING

Disabling IGMP snooping

Before implementing IGMP snooping

Placement of IGMP servers

The default setting for IGMP snooping is enabled. To disable it, enter the SET VBRIDGE <X> IGMP_SNOOPING DISABLE command.

Before you implement IGMP snooping within your network, be aware of how the CoreBuilder® 5000 SwitchModule and your software vendor’s multicast applications function with respect to IGMP. Inherently, all IGMP-compliant viewer applications on your network issue IGMP Membership Report packets (in response to IGMP Query Packets sent out from a local IGMP-compliant switch or router) requesting either to start or to continue sending the multicast stream to that port. However, some multicast applications do not send IGMP reports onto the network from the broadcasting server.

Depending on how your network is configured, broadcasters that do not send report packets onto the network can potentially cause excessive flooding for that vbridge or subnet. The CoreBuilder 5000 filters multicast traffic on a per-stream basis after receiving an IGMP report packet on the local vbridge or subnet. If IGMP report packets are never seen for a particular multicast session, that stream continues to flood within that vbridge or subnet. This situation may appear as if IGMP snooping is not functioning properly, when actually it is the limitation of the broadcasting application that fails to send IGMP Report packets to the querying switch or router on that subnet.

Placement of IGMP multicast servers that do not issue IGMP Report packets is critical to the proper functioning of IGMP snooping on the CoreBuilder 5000 product. If your IGMP Broadcasting application does not issue IGMP report packets, 3Com recommends that you either place at least one multicast client within the same subnet or vbridge as the IGMP multicast server or run the viewer software at the same time on the broadcasting server.