Question 317 of 2,152

EIGRP Troubleshooting →hardMultiple ChoiceObjective-mapped

Why EIGRP Convergence Is Slow in Large Hub-and-Spoke

This 300-410 practice question tests your understanding of eigrp troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

An engineer is troubleshooting an EIGRP convergence issue. After a link failure, the network takes an unusually long time to converge. The engineer notices that the EIGRP hello and hold timers are set to the default values. The network has many routers in a hub-and-spoke topology. What is the most likely cause of the slow convergence?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The hub router has too many EIGRP neighbors, causing CPU overload and dropped hello packets.
Correct because a high number of neighbors can overwhelm the hub, leading to missed hello packets and adjacency resets, which prolongs convergence.
B
The EIGRP stub feature is not enabled on the spoke routers.
Why wrong: Incorrect because stub routing helps reduce query propagation, but it does not directly affect hello/hold timer issues or convergence time due to neighbor count.
C
The EIGRP variance command is configured, causing unequal-cost load balancing.
Why wrong: Incorrect because variance does not affect convergence time; it only affects path selection.
D
The EIGRP router ID is not configured, so it defaults to the highest loopback IP.
Why wrong: Incorrect because the router ID does not impact convergence time; it is used for route identification.

Full breakdown with real-world context →

Quick Answer

The answer is the hub router’s CPU overload caused by too many EIGRP neighbors, which leads to dropped hello packets and adjacency resets. In a large hub-and-spoke topology, the hub must process hello packets, updates, and queries from every spoke; with default hello and hold timers (5 and 15 seconds), a hub managing dozens or hundreds of neighbors can become overwhelmed, causing it to miss hello packets and tear down adjacencies, which then must be re-established—dramatically slowing convergence. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how EIGRP’s default timers interact with scale, and a common trap is assuming slow convergence is due to route summarization or query scoping rather than control-plane congestion. Remember: when you see “hub-and-spoke” and “default timers” together, think “neighbor count overload.” A useful memory tip is “Too many spokes, the hub chokes.”

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 hub router has too many EIGRP neighbors, causing CPU overload and dropped hello packets.

In a hub-and-spoke EIGRP topology, the hub router maintains a large number of neighbor adjacencies. When a link failure occurs, the hub must process many queries and replies, which can overwhelm its CPU. If the CPU is overloaded, hello packets may be dropped, causing neighbor hold timers to expire and triggering unnecessary route recomputations. This leads to the observed slow convergence, even though hello and hold timers are at default values.

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.

✓
The hub router has too many EIGRP neighbors, causing CPU overload and dropped hello packets.
Why this is correct
Correct because a high number of neighbors can overwhelm the hub, leading to missed hello packets and adjacency resets, which prolongs convergence.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The EIGRP stub feature is not enabled on the spoke routers.
Why it's wrong here
Incorrect because stub routing helps reduce query propagation, but it does not directly affect hello/hold timer issues or convergence time due to neighbor count.
✗
The EIGRP variance command is configured, causing unequal-cost load balancing.
Why it's wrong here
Incorrect because variance does not affect convergence time; it only affects path selection.
✗
The EIGRP router ID is not configured, so it defaults to the highest loopback IP.
Why it's wrong here
Incorrect because the router ID does not impact convergence time; it is used for route identification.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that slow convergence is always due to timer mismatches or stub configuration, but the trap here is that default timers are fine and the real issue is hub CPU overload from excessive neighbor processing, which causes hello packet drops.

Detailed technical explanation

How to think about this question

EIGRP uses Reliable Transport Protocol (RTP) for hello packets, which are sent as unreliable multicast (224.0.0.10) by default every 5 seconds on LAN interfaces. When the hub router's CPU is saturated due to processing a large number of neighbor queries and updates, it may fail to send or process these hello packets within the 15-second hold time, causing neighbor loss and triggering a new Diffusing Update Algorithm (DUAL) computation. In real-world deployments, this is often mitigated by using EIGRP stub routing on spokes or by implementing route summarization to limit query scope.

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.

Quick reference

Routing Protocol Comparison

Protocol	Metric	Max Hops	Algorithm	Type
RIP v2	Hop count	15	Bellman-Ford	Distance vector
OSPF	Cost (bandwidth)	Unlimited	Dijkstra (SPF)	Link state
EIGRP	Composite metric	Unlimited	DUAL	Hybrid
IS-IS	Cost	Unlimited	Dijkstra	Link state
BGP	Policy / attributes	Unlimited	Path vector	Path vector

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

What to study next

Got this wrong? Here's your next step.

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

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FAQ

Questions learners often ask

What does this 300-410 question test?

EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The hub router has too many EIGRP neighbors, causing CPU overload and dropped hello packets. — In a hub-and-spoke EIGRP topology, the hub router maintains a large number of neighbor adjacencies. When a link failure occurs, the hub must process many queries and replies, which can overwhelm its CPU. If the CPU is overloaded, hello packets may be dropped, causing neighbor hold timers to expire and triggering unnecessary route recomputations. This leads to the observed slow convergence, even though hello and hold timers are at default values.

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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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