Which protocol does a receiver use to register their interest in multicast traffic at the first-hop router?
- IGMP
- Anycast-RP
- PIM-SM
- PIM-DM
Explanation: The Internet Group Management Protocol (IGMP) is the specific protocol used by IP hosts (receivers) to report their multicast group membership to their first-hop multicast routers. Its primary purpose is to allow these hosts to communicate their desire to receive specific multicast traffic to the local router, which then begins forwarding that traffic onto the network segment.
In contrast, other protocols mentioned serve different functions:
- PIM-SM (Sparse Mode) and PIM-DM (Dense Mode) are multicast routing protocols used between routers to build distribution trees and forward traffic across the network.
- Anycast-RP is a technique used to provide redundancy and load sharing for Rendezvous Points within a PIM-SM environment, rather than for host-to-router registration.
While receivers use IGMP to register with their local (first-hop) router, that router then uses protocols like PIM to communicate that membership information to the rest of the network.
Related exam: Modules 8 – 13: Checkpoint Exam: Network Routing Answers (CCNP ENCOR v9)
