Internet Group Management Protocol (Igmp); Igmp Implementation Information; Igmp Protocol Overview; Igmp Version 2 - Dell S4048–ON Configuration Manual

S-series 10gbe switches

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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.

Dell Networking Operating System (OS) supports IGMP versions 1, 2, and 3 based on RFCs 1112, 2236, and 3376, respectively.

Dell Networking OS does not support IGMP version 3 and versions 1 or 2 on the same subnet.

IGMP on Dell Networking OS supports 95 interfaces on S4810 and S4820 and an unlimited number of groups on all other

Dell Networking systems cannot serve as an IGMP host or an IGMP version 1 IGMP Querier.

Dell Networking OS automatically enables IGMP on interfaces on which you enable a multicast routing protocol.

IGMP has three versions. Version 3 obsoletes and is backwards-compatible with version 2; version 2 obsoletes version 1.

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.

IGMP messages are encapsulated in IP packets, as shown in the following illustration.

Internet Group Management Protocol (IGMP)