The answer is that auto-summary is disabled by default in EIGRP on Cisco IOS-XE. This is correct because modern EIGRP implementations, starting with IOS-XE, no longer automatically summarize routes at classful boundaries; instead, they advertise subnets with their exact prefix lengths. This change prevents routing loops and black holes that commonly occur in discontiguous networks, where classful summarization would incorrectly assume contiguous addressing. On the Cisco CCNP ENARSI 300-410 exam, this distinction tests your understanding of EIGRP’s evolution from legacy behavior—where auto-summary was enabled by default in older IOS versions—to the current default-off state. A common trap is assuming the old default still applies, so remember that on IOS-XE, you must explicitly enable auto-summary if you want classful behavior. Memory tip: think “IOS-XE, no summary for me”—auto-summary is off, so EIGRP advertises every subnet individually.
300-410 Device Access Control Practice Question
This 300-410 practice question tests your understanding of device access control. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 statement accurately describes the default behavior of auto-summary in EIGRP on Cisco IOS-XE?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Auto-summary is disabled by default, and EIGRP advertises subnets without automatic summarization.
In Cisco IOS-XE, EIGRP auto-summary is disabled by default. This means that EIGRP advertises subnets without automatically summarizing them at classful boundaries, allowing for more granular route advertisement and preventing routing issues in discontiguous networks.
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.
✗
Auto-summary is enabled by default, causing EIGRP to summarize at classful boundaries.
Why it's wrong here
This was true in older IOS versions, but auto-summary is now disabled by default in IOS-XE.
✓
Auto-summary is disabled by default, and EIGRP advertises subnets without automatic summarization.
Why this is correct
Correct. IOS-XE defaults to no auto-summary, preserving subnet information.
Related concept
Read the scenario before looking for a memorised answer.
✗
Auto-summary is enabled by default but only for external routes.
Why it's wrong here
Auto-summary applies to all EIGRP routes, not just external ones, and it is disabled by default.
✗
Auto-summary is disabled by default unless the network is configured with a classful mask.
Why it's wrong here
The default is disabled regardless of the network mask configuration.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that auto-summary is still enabled by default in EIGRP on modern IOS-XE, when in fact it was changed to disabled by default starting from IOS 15.0(1)M and later.
Detailed technical explanation
How to think about this question
Under the hood, EIGRP auto-summary, when enabled, automatically summarizes routes to their classful network boundary (e.g., 10.0.0.0/8 for a 10.1.1.0/24 subnet) before advertising them out interfaces. This can cause routing black holes in discontiguous networks where subnets of the same classful network are separated by another network. In modern networks, auto-summary is typically disabled to support VLSM and CIDR, and the 'no auto-summary' command is used explicitly in older configurations to ensure proper routing.
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 segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Device Access Control — This question tests Device Access Control — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Auto-summary is disabled by default, and EIGRP advertises subnets without automatic summarization. — In Cisco IOS-XE, EIGRP auto-summary is disabled by default. This means that EIGRP advertises subnets without automatically summarizing them at classful boundaries, allowing for more granular route advertisement and preventing routing issues in discontiguous networks.
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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Question Discussion
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