PLANET XGS3-24042 - Manual (Page 442)

48-41
Server 210.1.1.1 is distributing important multicast data on group 239.1.2.3, we can 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.
48.8.4 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.
48.9 IGMP
48.9.1 Introduction to IGMP
IGMP (Internet Group Management Protocol) is the protocol in TCP/IP protocol family which is responsible for
IP multicast member management. It is used to set up and maintain multicast group member relationship
between IP host and its neighbor multicast switches. IGMP does not include the spread and maintenance of
relation information of group members among multicast switches, this work is accomplished by each multicast
routing protocol. All hosts participating in multicast must implement IGMP protocol.
Hosts participating IP multicast can join in and exit multicast group at any location, any time and without limit
of member total. Multicast switch does not need and not likely to save all relationships of all hosts. It only gets
to know if there are receivers of some multicast group, i.e. group member, on the network segment each
interface connects to. And the host only needs to save which multicast groups it joined.
IGMP is asymmetric between host and router: the host needs to respond the IGMP query messages of
multicast switches, i.e. to report message response in membership; the switch sends out membership query
messages periodically, and then determine if there are hosts of some specific group joining in the sub-network
it belongs to based on the received response message, and send out query of specific group (IGMP version2)
when receiving the report of a host exiting the group to determine if there exists no member in some specific
group.
Up to now, there are three versions of IGMP: IGMP version1 (defined by RFC1112), IGMP version2 (defined
by RFC2236) and IGMP version3 (defined by RFC3376).
The main improvements of IGMP version2 over version1 are:
1. The election mechanism of multicast switches on the shared network segment
Shared network segment is the situation of there is more than one multicast switch on a network segment.