hardMultiple Select
350-401 Practice Question: Which three statements about EIGRP packet types…
Which three statements about EIGRP packet types are true? (Choose three.)
⚠ Common exam trap
Test-takers frequently confuse which EIGRP packet types are reliable versus unreliable, and whether they are sent as multicast or unicast. Candidates often mistakenly think all Update packets are multicast or that Reply packets are unreliable.
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
✓
Hello packets are sent unreliably and do not require an acknowledgment.
Option A is correct because EIGRP Hello packets are sent to the multicast address 224.0.0.10 using an unreliable delivery method and are not acknowledged, serving only for neighbor discovery and keepalive. Option C is correct because Query packets are sent reliably, meaning they require an acknowledgment, and each neighbor must respond with a Reply packet to indicate it has processed the query. Option D is correct because ACK packets are unicast to the sender of a reliable EIGRP packet and contain no data, existing solely to acknowledge receipt of reliable packets such as Updates, Queries, and Replies. Option B is incorrect because Update packets are not always multicast; they can be sent as unicast when replying to a specific neighbor or during initial neighbor formation. Option E is incorrect because Reply packets are sent reliably and require acknowledgment, not unreliably, to ensure the querying router receives the response.
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 packets are sent unreliably and do not require an acknowledgment.
Why this is correct
EIGRP Hello packets use the unreliable RTP path, so they carry no sequence number and are never acknowledged. This satisfies the stem's requirement for a true statement about packet types: neighbours detect each other and maintain adjacency through periodic, unacknowledged multicasts rather than reliable delivery.
- ✗
Update packets are always sent as multicast to all EIGRP neighbors.
Why it's wrong here
Update packets are sent unicast during initial topology exchange and can also be multicast, so "always multicast" is false. It is tempting because multicast updates do occur on multi-access segments, but unicast is required when a new neighbour is discovered or when responding to a specific neighbour.
- ✓
Query packets are sent reliably and require a Reply from each neighbor.
Why this is correct
EIGRP Query packets use reliable multicast transport, so each neighbour must acknowledge receipt; a neighbour lacking a feasible successor replies with a unicast Reply, and the router waits for every outstanding Reply before the route leaves Active state. This satisfies the stem's requirement for a reliably delivered packet type demanding per-neighbour response.
- ✓
ACK packets are unicast and are used to acknowledge reliable EIGRP packets.
Why this is correct
ACK packets travel unicast to the originating neighbour, confirming receipt of reliable EIGRP packets such as Updates, Queries and Replies. This satisfies the stem's requirement for a true statement about packet types, since acknowledgements must be directed to a single sender rather than multicast to the group.
- ✗
Reply packets are sent unreliably to conserve bandwidth.
Why it's wrong here
Incorrect because Reply packets are sent reliably (require acknowledgment) to ensure the querying router receives the information.
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.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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