- A
The EIGRP neighbor relationship is up, but authentication is failing intermittently.
Why wrong: The neighbor relationship cannot form because authentication fails on every packet.
- B
The MD5 key ID or key string does not match between R1 and 10.1.1.2, preventing neighbor formation.
The integrity check failure indicates a key mismatch, which blocks neighbor adjacency.
- C
EIGRP is using plain-text authentication and the key is incorrect.
Why wrong: The debug explicitly states MD5 authentication, not plain-text.
- D
The neighbor 10.1.1.2 is not configured for EIGRP authentication.
Why wrong: The packet includes authentication, so the neighbor is configured, but the keys do not match.
Question 1,348 of 2,152
300-410 EIGRP Troubleshooting Practice Question
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.
A network engineer runs the following command to troubleshoot an EIGRP issue:
R1# debug eigrp packets hello *Mar 1 00:05:23.123: EIGRP: received packet with MD5 authentication, key id = 1 *Mar 1 00:05:23.123: EIGRP: int GigabitEthernet0/0, src 10.1.1.2 dst 224.0.0.10, seq 0, ttl 1, opcode = 1 (Hello) *Mar 1 00:05:23.123: EIGRP: authentication failed for packet from 10.1.1.2, key id = 1, integrity check failed
What does this output indicate?
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 MD5 key ID or key string does not match between R1 and 10.1.1.2, preventing neighbor formation.
The debug output shows an EIGRP packet with MD5 authentication was received from 10.1.1.2, but the integrity check failed. This indicates that the MD5 key ID or key string configured on R1 does not match the one on the neighbor, which prevents the neighbor relationship from forming. The 'integrity check failed' message is a definitive sign of an authentication mismatch, not an intermittent issue.
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 EIGRP neighbor relationship is up, but authentication is failing intermittently.
Why it's wrong here
The neighbor relationship cannot form because authentication fails on every packet.
- ✓
The MD5 key ID or key string does not match between R1 and 10.1.1.2, preventing neighbor formation.
Why this is correct
The integrity check failure indicates a key mismatch, which blocks neighbor adjacency.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
EIGRP is using plain-text authentication and the key is incorrect.
Why it's wrong here
The debug explicitly states MD5 authentication, not plain-text.
- ✗
The neighbor 10.1.1.2 is not configured for EIGRP authentication.
Why it's wrong here
The packet includes authentication, so the neighbor is configured, but the keys do not match.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between authentication failure due to a mismatch (which prevents neighbor formation) versus intermittent packet loss or misconfiguration of the authentication mode (e.g., confusing MD5 with plain-text).
Detailed technical explanation
How to think about this question
EIGRP MD5 authentication uses a shared secret key and key ID to compute a hash that is appended to each packet; the receiving router recomputes the hash and compares it to the received value. If the keys or key IDs do not match, the integrity check fails, and the packet is silently dropped, preventing neighbor adjacency. In real-world scenarios, this often occurs after a key rollover if the new key is not synchronized across all routers in the EIGRP domain.
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
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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 MD5 key ID or key string does not match between R1 and 10.1.1.2, preventing neighbor formation. — The debug output shows an EIGRP packet with MD5 authentication was received from 10.1.1.2, but the integrity check failed. This indicates that the MD5 key ID or key string configured on R1 does not match the one on the neighbor, which prevents the neighbor relationship from forming. The 'integrity check failed' message is a definitive sign of an authentication mismatch, not an intermittent issue.
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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