easyMultiple Choice
350-401 Practice Question: An engineer is configuring multicast on a Cisco…
An engineer is configuring multicast on a Cisco router. The router receives multicast traffic from a source on interface GigabitEthernet0/0 and needs to forward it to receivers on interface GigabitEthernet0/1. The engineer enables PIM sparse mode on both interfaces and configures a static RP. However, the router does not create a multicast routing entry for the (S,G) pair. What is the most likely missing configuration?
⚠ Common exam trap
Cisco often tests the prerequisite of 'ip multicast-routing' as a hidden requirement, leading candidates to focus on PIM modes or RP configuration while overlooking the fundamental global enablement command.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The global command 'ip multicast-routing' is not configured.
The most likely missing configuration is the global command 'ip multicast-routing'. Without this command, the router cannot enable multicast forwarding or build multicast routing tables, regardless of PIM configuration on interfaces or static RP definition. PIM sparse mode and RP configuration are dependent on multicast routing being globally enabled first.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The global command 'ip multicast-routing' is not configured.
Why this is correct
The global command 'ip multicast-routing' is a prerequisite for any multicast forwarding on a Cisco router. Without this command, the router does not build the multicast routing table (mroute) nor run Protocol Independent Multicast (PIM), so even if packets arrive on GigabitEthernet0/0, they are treated as ordinary unicast traffic and no (S,G) or (*,G) entry is created. This is the root cause because all other configuration—interface IP addresses, PIM, and RP knowledge—is irrelevant until multicast routing is enabled.
- ✗
The interface GigabitEthernet0/0 is not configured with an IP address.
Why it's wrong here
For an interface to receive and process multicast traffic, it must have an IP address assigned, because the router needs an interface IP for PIM neighbor discovery and reverse-path-forwarding (RPF) checks. The scenario implies that traffic is arriving on GigabitEthernet0/0, which cannot happen if the interface has no IP address—the interface would be operationally down or ignore the packets. Therefore, while an IP address is necessary, its absence is not the cause of the multicast forwarding failure here.
- ✗
The RP address is not reachable from the router.
Why it's wrong here
An unreachable RP affects only PIM sparse-mode operations such as join requests and register messages, but it does not prevent a directly connected source from creating an (S,G) entry in the local multicast routing table. The router can still forward traffic from a directly connected source to interested receivers if multicast routing is enabled, because the source path is known through the unicast RIB. Since the problem is that no multicast forwarding occurs at all, the inability to reach the RP cannot be the underlying reason.
- ✗
The router is not configured as a candidate RP.
Why it's wrong here
A router does not need to be a candidate RP to forward multicast traffic; the RP is simply a meeting point for shared trees and is discovered via static configuration, Auto-RP, or BSR. Any router with multicast routing enabled and PIM on its interfaces can create forwarding state and send or receive multicast traffic as long as it knows the RP for the group. The absence of a candidate-RP configuration on this router does not disable multicast forwarding, so it is not the cause of the failure.
Go deeper
Related to this question
About these practice questions
One of 1,923 original 350-401 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.