Chapter 6 Igmp Configuration; Overview; Introduction To Igmp; Igmp Version - H3C S7500 Series Operation Manual

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Operation Manual – Multicast

H3C S7500 Series Ethernet Switches

Chapter 6 IGMP Configuration

Internet group management protocol (IGMP) is responsible for the management of IP

multicast members. It is used to establish and maintain membership between IP hosts

and their directly connected neighboring multicast routers.

However, the IGMP feature does not transmit and maintain the membership

information between multicast routers. This task is completed by multicast routing

protocols. All multicast host must have IGMP enabled.

IGMP is divided into two function parts:

Host side: an IP multicast host can join or exit a multicast group anywhere and

anytime, without being restricted by the total number of group members.

Router side: through the IGMP protocol, a multicast router checks the network

segment connected with each interface to see whether there are receivers of a

multicast group, namely, group members.

A multicast router need not and cannot save the membership information of all the

hosts. However, a host must save the information about the multicast groups it joins in.

IGMP is asymmetric between the host and the router. The host needs to use IGMP

report messages to respond to the IGMP query messages of the multicast routers. The

multicast router sends IGMP general query messages periodically and determines

whether any host of a specified group joins in its subnet based on the received

response messages. When the router receives IGMP leave messages, it will send

IGMPv2 group-specific query messages to find out whether the specified group still has

IGMP has three versions until now, including: IGMPv1 defined by RFC1112, IGMPv2

defined by RFC2236 and IGMPv3. IGMPv2 is the most widely used currently.

Compared with IGMPv1, the advantages of IGMPv2 are:

I. Multicast router election mechanism on a shared network segment

A shared network segment is a network segment with multiple multicast routers. In this

case, all routers running IGMP on this network segment can receive the membership

report messages from hosts. Therefore, only one router is necessary to send

Chapter 6 IGMP Configuration

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