easyMultiple Choice
300-410 Practice Question: Which statement correctly describes the default…
Which statement correctly describes the default behavior of EIGRP auto-summary on Cisco IOS-XE?
⚠ Common exam trap
Cisco often tests the change in default behavior between older IOS and IOS-XE, where candidates may incorrectly assume auto-summary is still enabled by default based on legacy knowledge.
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, so subnets are advertised without summarization.
In Cisco IOS-XE, EIGRP auto-summary is disabled by default. This means that EIGRP advertises subnets without summarizing them to their classful boundaries, preserving the original prefix lengths. This behavior changed from older IOS versions where auto-summary was enabled by default, which could cause routing issues 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, summarizing classful boundaries.
Why it's wrong here
On Cisco IOS-XE, EIGRP auto-summary is disabled by default; summarisation at classful boundaries must be enabled manually. It is tempting because older IOS releases did enable it by default, but IOS-XE changed that default, so the statement describes legacy behaviour.
- ✓
Auto-summary is disabled by default, so subnets are advertised without summarization.
Why this is correct
Cisco IOS-XE ships with EIGRP auto-summary disabled, so classful boundary summarisation never occurs unless explicitly enabled with the auto-summary command. This default satisfies the stem's requirement for accurate subnet advertisement, since each subnet is propagated individually rather than collapsed into its major classful network.
- ✗
Auto-summary is enabled only for EIGRP named mode configurations.
Why it's wrong here
Auto-summary defaults to enabled on IOS-XE for classic EIGRP configuration mode as well, so restricting it to named mode misstates the behaviour. It is tempting because named mode is the modern configuration style, yet the default applies across both modes unless explicitly disabled with no auto-summary.
- ✗
Auto-summary is disabled by default, but only for IPv6 EIGRP.
Why it's wrong here
This applies to both IPv4 and IPv6; auto-summary is IPv4-specific and disabled by default.
Visual reference
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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