IPv4 Multicast Protocol
367
configure on its join-in switch as follows:
Switch(config)#ip multicast policy 210.1.1.1/32 239.1.2.3/32 cos 4
In this way, the multicast stream will have a priority of value 4 (Usually this is pretty
higher, the higher possible one is protocol data; if higher priority is set, when there is too
many multicast data, it might cause abnormal behavior of the switch protocol) when it gets
to other switches through this switch.
43.2.4
DCSCM Troubleshooting
The effect of DCSCM module itself is similar to ACL, and the problems occurred are
usually related to improper configuration. Please read the descriptions above carefully. If
you still can not determine the cause of the problem, please send your configurations and
the effects you expect to the after-sale service staff of our company.
43.3
IGMP Snooping
43.3.1
Introduction to IGMP Snooping
IGMP (Internet Group Management Protocol) is a protocol used in IP multicast. IGMP
is used by multicast enabled network device (such as a router) for host membership query,
and by hosts that are joining a multicast group to inform the router to accept packets of a
certain multicast address. All those operations are done through IGMP message
exchange. The router will use a multicast address (224.0.0.1) that can address to all hosts
to send an IGMP host membership query message. If a host wants to join a multicast
group, it will reply to the multicast address of that a multicast group with an IGMP host
membership reports a message.
IGMP Snooping is also referred to as IGMP listening. The switch prevents multicast
traffic from flooding through IGMP Snooping, multicast traffic is forwarded to ports
associated to multicast devices only. The switch listens to the IGMP messages between
the multicast router and hosts, and maintains multicast group forwarding table based on
the listening result, and can then decide to forward multicast packets according to the
forwarding table.
Switch provides IGMP Snooping and is able to send a query from the switch so that
the user can use switch in IP multicast.