Question 642 of 2,152
Device ManagementmediumMultiple ChoiceObjective-mapped

Running OSPF and PIM Sparse-Mode Simultaneously

This 300-410 practice question tests your understanding of device management. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Given the following partial configuration on router R5:

interface GigabitEthernet0/0
 ip address 10.1.1.1 255.255.255.0
 ip pim sparse-mode

!

interface GigabitEthernet0/1
 ip address 10.2.2.1 255.255.255.0
 ip pim sparse-mode

!

router ospf 1

router-id 5.5.5.5

network 10.0.0.0 0.255.255.255 area 0

What is the effect of this configuration?

Quick Answer

The answer is that OSPF will form adjacencies on both interfaces, and PIM sparse-mode will operate normally; the configuration is valid. This works because OSPF and PIM sparse-mode operate at different layers of the routing stack—OSPF handles unicast topology discovery and loop-free path selection, while PIM sparse-mode manages multicast distribution tree construction and relies on the unicast routing table provided by OSPF. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that enabling both protocols on the same interface is not only allowed but is standard practice for multicast-enabled networks; a common trap is assuming that PIM sparse-mode requires a dedicated multicast routing protocol like DVMRP or that OSPF’s network statement would interfere with PIM’s operation. In reality, OSPF’s network command simply includes the interface in the OSPF process, and PIM sparse-mode independently uses the resulting unicast routes to build its Reverse Path Forwarding (RPF) checks. A helpful memory tip: “OSPF builds the map, PIM follows the path”—they coexist without conflict because one provides the route, the other uses it.

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

OSPF will form adjacencies on both interfaces, and PIM sparse-mode will operate normally; the configuration is valid.

The configuration is valid because OSPF and PIM sparse-mode operate independently on an interface. OSPF uses multicast address 224.0.0.5/6 for hello packets and forms adjacencies regardless of PIM sparse-mode being enabled. PIM sparse-mode requires an RP to function, but its presence does not affect OSPF adjacency formation. The network statement 10.0.0.0 0.255.255.255 matches both interfaces (10.1.1.1 and 10.2.2.1), so OSPF will form adjacencies on both.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • OSPF will not form adjacencies because PIM sparse-mode is enabled on the interfaces.

    Why it's wrong here

    OSPF and PIM can coexist on the same interface. PIM does not interfere with OSPF adjacency formation.

  • OSPF will form adjacencies on both interfaces, and PIM sparse-mode will operate normally; the configuration is valid.

    Why this is correct

    Both protocols work together. OSPF handles unicast routing, PIM handles multicast. No issues.

    Related concept

    Read the scenario before looking for a memorised answer.

  • OSPF will only form adjacency on GigabitEthernet0/0 because the network statement does not match GigabitEthernet0/1.

    Why it's wrong here

    The network statement 10.0.0.0 0.255.255.255 matches both 10.1.1.0/24 and 10.2.2.0/24.

  • PIM sparse-mode will not work because there is no rendezvous point (RP) configured.

    Why it's wrong here

    PIM sparse-mode can operate without a statically configured RP if dynamic RP discovery (e.g., Auto-RP or BSR) is used, or if the RP is learned via other means. The absence of an RP does not prevent PIM from operating, but multicast forwarding may be limited.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that enabling PIM sparse-mode on an interface disrupts OSPF adjacency formation, when in fact they operate at different layers (OSPF at Layer 3 routing, PIM at multicast routing) and do not interfere with each other.

Detailed technical explanation

How to think about this question

OSPF uses IP protocol 89 and relies on its own multicast groups (224.0.0.5 for all OSPF routers, 224.0.0.6 for DR/BDR) for neighbor discovery and adjacency maintenance, which are independent of PIM's multicast routing. PIM sparse-mode uses 224.0.0.13 for hello messages, and while both protocols may share the same interface, they do not conflict. In real-world deployments, it is common to enable both OSPF and PIM on the same interface for underlay routing and multicast overlay, but an RP must be configured (e.g., via static RP, Auto-RP, or BSR) before PIM sparse-mode can actually forward multicast traffic.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

Visual reference

R1 R2 R3 R4 10 100 10 100 OSPF picks R1→R2→R4 (cost 20) over R1→R3→R4 (cost 200)

Quick reference

Routing Protocol Comparison

ProtocolMetricMax HopsAlgorithmType
RIP v2Hop count15Bellman-FordDistance vector
OSPFCost (bandwidth)UnlimitedDijkstra (SPF)Link state
EIGRPComposite metricUnlimitedDUALHybrid
IS-ISCostUnlimitedDijkstraLink state
BGPPolicy / attributesUnlimitedPath vectorPath vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

What to study next

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FAQ

Questions learners often ask

What does this 300-410 question test?

Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: OSPF will form adjacencies on both interfaces, and PIM sparse-mode will operate normally; the configuration is valid. — The configuration is valid because OSPF and PIM sparse-mode operate independently on an interface. OSPF uses multicast address 224.0.0.5/6 for hello packets and forms adjacencies regardless of PIM sparse-mode being enabled. PIM sparse-mode requires an RP to function, but its presence does not affect OSPF adjacency formation. The network statement 10.0.0.0 0.255.255.255 matches both interfaces (10.1.1.1 and 10.2.2.1), so OSPF will form adjacencies on both.

What should I do if I get this 300-410 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jul 4, 2026

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