User's Manual

48-46
(1) Configure SwitchA:
Switch(config)#ip pim multicast-routing
Switch (config)#interface vlan 1
Switch(Config-if-Vlan1)#ip address 12.1.1.1 255.255.255.0
Switch(Config-if-Vlan1)#ip pim dense-mode
(2) Configure SwitchB:
Switch(config)#ip pim multicast-routing
Switch(config)#interface vlan1
Switch(Config-if-Vlan1)#ip address 12.1.1.2 255.255.255.0
Switch(Config-if-Vlan1)#ip pim dense-mode
Switch(Config-if-Vlan1)#exit
Switch(config)#interface vlan2
Switch(Config-if-Vlan1)#ip address 20.1.1.1 255.255.255.0
Switch(Config-if-Vlan2)#ip pim dense-mode
Switch(Config-if-Vlan2)#ip igmp version 3
48.9.4 IGMP Troubleshooting
In configuring and using IGMP Protocol, IGMP Protocol might not operate normally caused by physical
connection or incorrect configuration. Therefore, user should pay attention to the following issues:
 Firstly to assure that physical connection is correct;
 Next, to assure the Protocol of Interface and Link protocol is UP (use show interface command);
 Afterwards, to assure to start a kind of multicast protocol on the interface;
 Multicast Protocol requires RPF Check using unicast routing; therefore the correctness of unicast
routing must be assured beforehand.
48.10 IGMP Snooping
48.10.1 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