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300-410 Practice Question: In EIGRP, what is the default behavior of…
In EIGRP, what is the default behavior of auto-summary in IOS-XE versions 15.0 and later?
⚠ Common exam trap
The trap is remembering the old default (enabled) from legacy IOS and applying it to 15.0+, or assuming named mode changed the default — candidates must recall that 15.0 flipped auto-summary to disabled for both modes.
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
✓
Auto-summary is disabled by default.
Starting with Cisco IOS 15.0(1)M and IOS-XE 15.x, EIGRP auto-summary is disabled by default for both classic and named modes. This change aligned EIGRP with modern classless routing behavior and prevents the suboptimal routing caused by summarizing at classful boundaries.
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.
Why it's wrong here
Auto-summary was enabled by default in older IOS releases, but IOS-XE 15.0 and later changed this to disabled for both classic and named EIGRP modes. It is tempting because it matches legacy documentation and pre-15.0 behaviour, yet it contradicts the current default.
- ✓
Auto-summary is disabled by default.
Why this is correct
Auto-summary is disabled by default from IOS 15.0 onward, satisfying the question's version constraint. EIGRP therefore advertises subnet prefixes with their actual masks rather than collapsing them to classful boundaries, preventing the misleading routes and black holes that classful summarisation caused in discontiguous networks.
- ✗
Auto-summary is enabled only for EIGRP named mode.
Why it's wrong here
Named mode does not enable auto-summary; it is disabled there too, so this states the reverse of actual behaviour. It is tempting because named mode is the modern configuration style, but auto-summary defaults off in both classic and named modes on IOS-XE 15.0 and later.
- ✗
Auto-summary is disabled only for EIGRP classic mode.
Why it's wrong here
Auto-summary is disabled in both classic and named EIGRP modes on IOS-XE 15.0 and later, so restricting the change to classic mode is factually wrong. It is tempting because classic mode is where the historical enabled default applied, but the newer default covers both modes.
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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JA
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
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.