A wastewater plant has receiver VLANs with no multicast router attached, yet access switches still need periodic membership queries to refresh IGMP snooping state. Which role should be enabled on a switch in each such VLAN?
Select an answer to reveal the explanation.
Short Explanation
Snooping only works if something keeps asking “who still wants this channel?” Normally the multicast router sends those queries. When no router sits on the VLAN, an IGMP querier on a switch fills that job so membership state does not time out into a flood.
Full Explanation
At a wastewater plant, receiver VLANs with no attached multicast router still need someone to send periodic IGMP General Queries so hosts refresh membership and IGMP snooping tables stay accurate. Enabling an IGMP querier on a switch in each such VLAN provides that solicitation role. Without queries, snooping state ages out and many platforms revert toward flooding, undoing containment for plant telemetry and camera groups.
An MSDP peer for anycast RP advertisement across plants exchanges Source-Active information between RPs in sparse-mode designs. MSDP is not the LAN-edge query function required on a Layer-2-only receiver VLAN.
A PIM assert winner suppresses duplicate forwarders on a multi-access segment after routing is already in play. Assert does not generate IGMP membership queries for snooping refresh on a routerless VLAN.
An Auto-RP mapping agent flooding RP-discovery on 224.0.1.40 distributes RP-to-group mappings for PIM-SM. That control-plane role is unrelated to soliciting host IGMP reports on an L2 receiver segment.
Exam caveat: if a real multicast router later appears on the VLAN, querier election based on IP address typically yields to the router; duplicate queriers should be intentional and monitored rather than accidental.
Operational check: enable IGMP querier on one switch per plant receiver VLAN, verify periodic General Queries with a capture or switch counters, and confirm snooping entries renew instead of expiring into flood. Note the querier IP and VLAN in the municipal OT runbook so maintenance windows do not silently remove the only query source.