Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 399
Internet Group Management Protocol (IGMP), IGMP Implementation Information, IGMP Protocol Overview
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21 Internet Group Management Protocol (IGMP) Internet group management protocol (IGMP) is a Layer 3 multicast protocol that hosts use to join or leave a multicast group. Multicast is premised on identifying many hosts by a single destination IP address; hosts represented by the same IP address are 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. IGMP Implementation Information • The Dell Networking OS supports IGMP versions 1, 2, and 3 based on RFCs 1112, 2236, and 3376, respectively. • The system does not support IGMP version 3 and versions 1 or 2 on the same subnet. • Dell Networking switches cannot serve as an IGMP host or an IGMP version 1 IGMP Querier. • The system automatically enables IGMP on interfaces on which you enable a multicast routing protocol. Topics: • IGMP Protocol Overview • Configure IGMP • Viewing IGMP Enabled Interfaces • Selecting an IGMP Version • Viewing IGMP Groups • Enabling IGMP Immediate-Leave • IGMP Snooping • Fast Convergence after MSTP Topology Changes • Designating a Multicast Router Interface IGMP Protocol 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 on 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. Internet Group Management Protocol (IGMP) 399
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