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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

    This was true in older IOS, but not in current IOS-XE.

  • Auto-summary is disabled by default, so subnets are advertised without summarization.

    Why this is correct

    Correct: In IOS-XE, auto-summary is off by default, preventing unwanted classful summarization.

  • Auto-summary is enabled only for EIGRP named mode configurations.

    Why it's wrong here

    Auto-summary behavior is not dependent on EIGRP mode; it is disabled by default in both classic and named modes.

  • 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

192.168.1.0 /24 256 addresses (254 usable) 192.168.1.0 /25 Subnet A 128 addr (126 usable) 192.168.1.128 /25 Subnet B 128 addr (126 usable) Borrowing 1 bit from host portion creates 2 subnets (/25)

Quick reference

Routing Protocol Comparison

ProtocolMetricMax HopsAlgorithmType
RIP v2Hop count15Bellman-FordDistance vector
OSPFCost (bandwidth)UnlimitedDijkstra (SPF)Link state
EIGRPComposite metricUnlimitedDUALHybrid
IS-ISCostUnlimitedDijkstraLink state
BGPPolicy / attributesUnlimitedPath vectorPath 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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