Which entity periodically sends IGMP Host Membership Queries?

On a multi-access network segment (like a LAN) with multiple multicast-enabled routers, an IGMP Querier election process takes place. The router with the lowest IP address is elected as the Querier. This single, elected Querier is solely responsible for periodically sending General Host Membership Queries to the all-systems multicast address (224.0.0.1). This mechanism discovers and maintains the state of multicast group memberships on the segment, ensuring that traffic is forwarded only to networks with interested receivers. Non-querier routers listen to membership reports but do not send periodic queries.

B. Hosts send IGMP Membership Reports in response to queries or to join a group; they do not send queries. The suppression timer relates to sending reports, not queries.

C. Multicast-enabled hosts are receivers that respond to queries with Membership Reports. They do not originate periodic Membership Queries.

D. The IGMP Querier election mechanism is specifically designed to prevent all routers from sending queries, which would cause unnecessary network traffic and protocol overhead.

E. Only the single elected Querier sends periodic queries. Other multicast-enabled routers on the LAN assume a non-querier role and do not perform this function.

1. Nokia SR OS R21.10.R1 IP Routing Protocols Guide, Section: IGMP. "On a shared-media LAN, one router is elected to be the IGMP Querier. The IGMP Querier is the router that periodically sends IGMP Host Membership Queries onto the LAN." (Reference to general IGMP Querier function).

2. IETF RFC 2236: Internet Group Management Protocol, Version 2, Section 4: Querier Election. "When a multicast router starts up, it is a Querier... If a router hears a Query message from a router with a lower IP address, it becomes a Non-Querier." This section details the election process that results in a single Querier.

3. IETF RFC 3376: Internet Group Management Protocol, Version 3, Section 4.1.1: Querier Election. "The Querier election mechanism is the same as in IGMPv2: the router with the lowest IP address on the subnet is elected the Querier." This confirms the single-querier principle is maintained in IGMPv3.

4. IETF RFC 2236: Internet Group Management Protocol, Version 2, Section 2.1: General Query. "General Queries are sent by the Querier to all hosts and routers on the attached network... to learn which groups have members on that network." This explicitly defines the Querier's role in sending these messages.