Manual

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Москва, Новозаводская ул., 18, стр. 1
244
Multicast strategy
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.
28.8.4 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.
28.9 IGMP
28.9.1 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: