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300-410 Practice Question: The default behavior of EIGRP auto-summary in…
What is the default behavior of EIGRP auto-summary in IOS-XE 15.x and later?
⚠ Common exam trap
Cisco often tests the misconception that auto-summary remains enabled by default in newer IOS versions, as it was in older releases, leading candidates to incorrectly select Option A.
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
In IOS-XE 15.x and later, EIGRP auto-summary is disabled by default. This change was introduced to align with modern network designs that require classless routing and to prevent unintended route summarization at classful boundaries, which can cause routing loops or suboptimal path selection in discontiguous networks.
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 is disabled by default in EIGRP on IOS-XE 15.x and later versions. This change was implemented to prevent potential routing black holes and suboptimal pathing issues arising from discontiguous networks, encouraging more precise manual summarisation. The option is tempting because auto-summary *was* enabled by default in older Cisco IOS releases, prior to IOS 15.x, where it automatically summarised routes at classful network boundaries, which many network engineers still recall as the traditional behaviour.
- ✓
Auto-summary is disabled by default
Why this is correct
Correct. IOS-XE 15.x and later disable auto-summary by default to avoid suboptimal routing.
- ✗
Auto-summary is enabled only for connected routes
Why it's wrong here
Incorrect. Auto-summary applies to all EIGRP routes when enabled.
- ✗
Auto-summary is disabled only for point-to-point links
Why it's wrong here
Incorrect. The default is global, not interface-specific.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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