Quick Answer
The answer is MD5. When you configure EIGRP authentication on a Cisco router, the default authentication mode is MD5, meaning that if you issue the `ip authentication mode eigrp` command without specifying a mode, the router automatically applies MD5 hashing for route authentication. This is because EIGRP was originally designed with MD5 as its only supported hashing algorithm, and while SHA-256 was later introduced for stronger security, it requires the explicit `hmac-sha-256` keyword in the configuration. On the Cisco CCNP ENARSI 300-410 exam, this concept often appears in questions about securing EIGRP adjacencies, and a common trap is assuming that SHA-256 is the default or that no authentication mode is set at all. Remember that MD5 is the legacy default, and SHA-256 is always an optional upgrade. A helpful memory tip: "MD5 is the default—SHA-256 needs the extra 'SHA' command."
This 300-410 practice question tests your understanding of eigrp troubleshooting. 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.
What is the default EIGRP authentication mode when authentication is configured?
SHA-256
Why wrong: Incorrect. SHA-256 is an option but not the default; it requires the 'hmac-sha-256' keyword.
MD5
Correct. EIGRP defaults to MD5 authentication when enabled.
Plain text
Why wrong: Incorrect. EIGRP does not support plain-text authentication.
No authentication by default
Why wrong: Incorrect. When authentication is configured, the mode must be specified; MD5 is the default if not specified.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
MD5
EIGRP supports MD5 authentication by default. When 'ip authentication mode eigrp' is configured, the default mode is MD5. SHA-256 requires additional configuration.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
SHA-256
Why it's wrong here
Incorrect. SHA-256 is an option but not the default; it requires the 'hmac-sha-256' keyword.
MD5
Why this is correct
Correct. EIGRP defaults to MD5 authentication when enabled.
Related concept
Read the scenario before looking for a memorised answer.
Plain text
Why it's wrong here
Incorrect. EIGRP does not support plain-text authentication.
No authentication by default
Why it's wrong here
Incorrect. When authentication is configured, the mode must be specified; MD5 is the default if not specified.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Keyword trap
Incorrect. SHA-256 is an option but not the default; it requires the 'hmac-sha-256' keyword.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
EIGRP Troubleshooting — study guide chapter
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Related practice questions
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FAQ
EIGRP Troubleshooting — This question tests EIGRP Troubleshooting — Read the scenario before looking for a memorised answer..
The correct answer is: MD5 — EIGRP supports MD5 authentication by default. When 'ip authentication mode eigrp' is configured, the default mode is MD5. SHA-256 requires additional configuration.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 18, 2026
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.
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