Question 1,187 of 2,152

Route Summarization →hardMultiple SelectObjective-mapped

Quick Answer

The correct answer is that manual summarization can be configured using the 'ip summary-address eigrp' command under interface configuration, while automatic summarization is enabled by default only for classful major network boundaries. This distinction is critical because EIGRP’s automatic summarization does not apply to all networks—it only summarizes routes at the classful boundary when the network is contiguous, and it is disabled by default in newer IOS versions. On the Cisco CCNP ENARSI 300-410 exam, this topic tests your ability to differentiate between the two methods and avoid the common trap of assuming automatic summarization works for all subnets or that manual summarization requires a route-map. Remember that manual summarization can be applied on any interface, not just serial links, and it creates a discard route to prevent routing loops. A helpful memory tip: “Auto is classful, manual is any interface—use the ‘summary-address’ command to take control.”

300-410 Route Summarization Practice Question

This 300-410 practice question tests your understanding of route summarization. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 TWO statements about route summarization in EIGRP are true? (Choose TWO.)

Question 1hardmulti select

Study the full EIGRP explanation →

A
EIGRP automatic summarization is enabled by default for classful networks.
By default, EIGRP summarizes routes at classful boundaries when automatic summarization is enabled.
B
Manual summarization can be configured using the 'ip summary-address eigrp' command under interface configuration.
This command is used to configure manual route summarization on a specific interface in EIGRP.
C
EIGRP supports automatic summarization for all types of networks, including discontiguous subnets.
Why wrong: Automatic summarization only works for classful boundaries and can cause issues with discontiguous subnets.
D
Route summarization in EIGRP requires the use of a route-map to define the summary prefix.
Why wrong: No route-map is required; the summary address is specified directly in the command.
E
Manual summarization can only be applied to serial interfaces.
Why wrong: Manual summarization can be applied to any interface, including Ethernet, FastEthernet, and others.

Full breakdown with real-world context →

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

✓

EIGRP automatic summarization is enabled by default for classful networks.

EIGRP supports manual summarization on any interface using the 'ip summary-address eigrp' command, and automatic summarization is enabled by default for classful networks. EIGRP does not support automatic summarization at the classful boundary for all networks; it is only for major network boundaries. Summarization in EIGRP does not require a route-map, and it can be configured on any interface, not just serial interfaces.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
EIGRP automatic summarization is enabled by default for classful networks.
Why this is correct
By default, EIGRP summarizes routes at classful boundaries when automatic summarization is enabled.
Related concept
CIDR notation defines the prefix length.
✓
Manual summarization can be configured using the 'ip summary-address eigrp' command under interface configuration.
Why this is correct
This command is used to configure manual route summarization on a specific interface in EIGRP.
Related concept
CIDR notation defines the prefix length.
✗
EIGRP supports automatic summarization for all types of networks, including discontiguous subnets.
Why it's wrong here
Automatic summarization only works for classful boundaries and can cause issues with discontiguous subnets.
✗
Route summarization in EIGRP requires the use of a route-map to define the summary prefix.
Why it's wrong here
No route-map is required; the summary address is specified directly in the command.
✗
Manual summarization can only be applied to serial interfaces.
Why it's wrong here
Manual summarization can be applied to any interface, including Ethernet, FastEthernet, and others.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Trap categories for this question

Command / output trap
No route-map is required; the summary address is specified directly in the command.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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.

What to study next

Got this wrong? Here's your next step.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this 300-410 question test?

Route Summarization — This question tests Route Summarization — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: EIGRP automatic summarization is enabled by default for classful networks. — EIGRP supports manual summarization on any interface using the 'ip summary-address eigrp' command, and automatic summarization is enabled by default for classful networks. EIGRP does not support automatic summarization at the classful boundary for all networks; it is only for major network boundaries. Summarization in EIGRP does not require a route-map, and it can be configured on any interface, not just serial interfaces.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

About these practice questions

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Same concept, more angles

2 more ways this is tested on 300-410

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. In EIGRP, what is the default administrative distance of a summary route created with the 'ip summary-address eigrp' command?

easy

✓ A.5
B.90
C.170
D.1

Why A: By default, EIGRP summary routes have an administrative distance of 5, which is lower than the default distance of 90 for internal EIGRP routes.

Variation 2. EIGRP stuck-in-active (SIA) is occurring due to route summarization. Router R1 is the hub in a hub-and-spoke topology with R2 and R3 as spokes. R1's configuration: interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.0 ip summary-address eigrp 100 10.0.0.0 255.255.252.0 ! router eigrp 100 network 10.0.0.0 ! R2 and R3 are connected via Frame Relay. R2 shows: R2# show ip eigrp topology 10.0.1.0/24 P 10.0.1.0/24, 1 successors, FD is 30720 via 10.0.0.1 (30720/28160), GigabitEthernet0/0 R3 has a similar entry. However, when R1's summary is active, R2 and R3 go into active state for the summary. What is the root cause?

hard

✓ A.The summary route causes EIGRP queries to loop between spokes when one loses connectivity, leading to SIA.
B.The Frame Relay network is not supporting multicast, so EIGRP hello packets are lost.
C.The summary route metric is too high, causing EIGRP to not install it.
D.EIGRP is not enabled on the spoke interfaces.

Why A: The summary route 10.0.0.0/22 is advertised by R1 to both spokes. If one spoke loses connectivity to R1, it queries the other spoke for the summary. The spoke may not have a route to the summary, causing it to query R1 again, leading to a query loop and SIA. The summary should be configured with a leak-map to allow specific routes, or the query scope should be limited.

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