Dell PowerEdge XL 5133-4 MXL 10/40GbE Switch IO Module FTOS Command Reference - Page 123
Internet Group Management Protocol (IGMP), IGMP Overview, IGMP Version 2
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9 Internet Group Management Protocol (IGMP) On an Aggregator, IGMP snooping is auto-configured. You can display information on IGMP by using show commands. Multicast is based on identifying many hosts by a single destination IP address. Hosts represented by the same IP address are a multicast group. The internet group management protocol (IGMP) is a Layer 3 multicast protocol that hosts use to join or leave a multicast group. Multicast routing protocols (such as protocol-independent multicast [PIM]) use the information in IGMP messages to discover which groups are active and to populate the multicast routing table. This chapter contains the following sections: • IGMP Overview • IGMP Snooping IGMP Overview IGMP has three versions. Version 3 obsoletes and is backwards-compatible with version 2; version 2 obsoletes version 1. IGMP Version 2 IGMP version 2 improves upon version 1 by specifying IGMP Leave messages, which allows hosts to notify routers that they no longer care about traffic for a particular group. Leave messages reduce the amount of time that the router takes to stop forwarding traffic for a group to a subnet (leave latency) after the last host leaves the group. In version 1 hosts quietly leave groups, and the router waits for a query response timer several times the value of the query interval to expire before it stops forwarding traffic. To receive multicast traffic from a particular source, a host must join the multicast group to which the source is sending traffic. A host that is a member of a group is called a "receiver." A host may join many groups, and may join or leave any group at any time. A host joins and leaves a multicast group by sending an IGMP message to its IGMP querier. The querier is the router that surveys a subnet for multicast receivers and processes survey responses to populate the multicast routing table. IGMP messages are encapsulated in IP packets (Figure 9-1). Internet Group Management Protocol (IGMP) | 109