- A
Hello
Why wrong: Hello packets are used for neighbor discovery and keepalive, not for acknowledgment.
- B
Update
Why wrong: Update packets contain routing information and are sent reliably.
- C
ACK
Correct: ACK packets are sent to confirm reliable delivery of updates, queries, and replies.
- D
Query
Why wrong: Query packets are used during the Diffusing Update Algorithm (DUAL) to search for alternate paths.
Question 777 of 2,152
EIGRP Reliable Transport: ACK Packets Confirm Update Receipt
This 300-410 practice question tests your understanding of device management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which EIGRP packet type is used to confirm receipt of an update during reliable transport?
Quick Answer
The answer is the ACK packet. In EIGRP’s Reliable Transport Protocol (RTP), ACK packets are used to confirm receipt of an update during reliable transport because RTP requires explicit acknowledgment for any multicast or unicast update to ensure delivery. An ACK is essentially a Hello packet with no data, sent as a unicast, and critically, it is always transmitted unreliably—meaning it does not itself require an acknowledgment, preventing an infinite loop of confirmations. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of EIGRP’s reliability mechanism, often appearing in questions about packet types or RTP behavior. A common trap is confusing ACK packets with Hello packets; remember that while both share the same format, ACKs are unicast and never acknowledged. Memory tip: “ACKs are the silent nod—no data, no reply, just a quick confirm.”
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
✓
ACK
C is correct because EIGRP uses a reliable transport protocol (RTP) to ensure delivery of certain packets like Updates, Queries, and Replies. The ACK packet is a lightweight, unreliable packet sent to explicitly acknowledge receipt of a reliable packet, confirming that the update was received without needing a full retransmission.
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.
- ✗
Hello
Why it's wrong here
Hello packets are used for neighbor discovery and keepalive, not for acknowledgment.
- ✗
Update
Why it's wrong here
Update packets contain routing information and are sent reliably.
- ✓
ACK
Why this is correct
Correct: ACK packets are sent to confirm reliable delivery of updates, queries, and replies.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Query
Why it's wrong here
Query packets are used during the Diffusing Update Algorithm (DUAL) to search for alternate paths.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the purpose of Hello packets (which are also small and frequent) with ACK packets, forgetting that Hellos are used for neighbor discovery and keepalive, not for reliable transport acknowledgment.
Detailed technical explanation
How to think about this question
EIGRP's Reliable Transport Protocol (RTP) uses sequence numbers to track reliable packets; when a router sends an Update or Query, it expects an ACK with the same sequence number within a retransmission timeout (RTO). ACK packets are sent as unicast and are not themselves acknowledged, making them lightweight and efficient. In real-world scenarios, a missing ACK triggers a retransmission, which can cause routing convergence delays if the network has high latency or packet loss.
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 practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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
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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: ACK — C is correct because EIGRP uses a reliable transport protocol (RTP) to ensure delivery of certain packets like Updates, Queries, and Replies. The ACK packet is a lightweight, unreliable packet sent to explicitly acknowledge receipt of a reliable packet, confirming that the update was received without needing a full retransmission.
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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