Question 988 of 2,152

VRF-Lite →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the summary route 10.0.0.0/8 is leaked into the global table without the specific 10.1.1.0/24 route, causing traffic to be dropped. This occurs because the route-map only matches the summary prefix via the prefix-list, so the more specific subnet remains isolated within VRF-A. When the global routing table installs the summary, it may point to a discard interface or simply lack the granularity to forward packets to 10.1.1.0/24, resulting in a VRF-Lite route leak of summary without specific route scenario. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding that route leaking requires explicit matching of each prefix; a summary does not automatically carry its constituent subnets. A common trap is assuming a summary provides recursive reachability, but without the specific route leaked, the global table cannot forward to the exact subnet. Memory tip: “Summary leaks are like a map with a state outline but no city streets—you’ll never find the house.”

300-410 VRF-Lite Practice Question

This 300-410 practice question tests your understanding of vrf-lite. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

Router R1 is leaking a summary route 10.0.0.0/8 from VRF-A into the global routing table, but hosts in the global table cannot reach subnet 10.1.1.0/24 within VRF-A. R1 configuration: ip vrf VRF-A, rd 100:1, route-target export 100:1, route-target import 100:1. Interface Gig0/0 in VRF-A has ip address 10.1.1.1 255.255.255.0. The leaking is done via route-map: route-map LEAK permit 10, match ip address prefix-list SUMMARY, set global. Prefix-list SUMMARY permits 10.0.0.0/8. What is the root cause?

Question 1hardmultiple choice

Read the full VRF explanation →

A
The summary route 10.0.0.0/8 is being installed in the global table, but the more specific route 10.1.1.0/24 is not leaked, causing traffic to be dropped.
Correct: The summary lacks the specific route; traffic to 10.1.1.0/24 matches the summary but may be discarded if the summary points to null or is not resolved.
B
The route-map should use match ip address prefix-list SPECIFIC instead of SUMMARY.
Why wrong: Incorrect: The intent is to leak a summary, but the specific route also needs to be leaked or the summary must point to a valid next-hop.
C
The VRF must have a default route to reach the global table.
Why wrong: Incorrect: The issue is about leaking from VRF to global, not the other direction.
D
The prefix-list should permit 10.1.1.0/24 only.
Why wrong: Incorrect: The summary is intended, but it fails to provide reachability to the specific subnet.

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

✓

The summary route 10.0.0.0/8 is being installed in the global table, but the more specific route 10.1.1.0/24 is not leaked, causing traffic to be dropped.

The summary route 10.0.0.0/8 covers the more specific subnet 10.1.1.0/24, but the route-map only leaks the summary, not the specific. When the global table has the summary, traffic to 10.1.1.0/24 is forwarded based on the summary, but since the specific route is not leaked, the packet may be dropped or sent to a null interface if the summary points to a discard. The issue is that the summary route does not provide reachability to the specific subnet because the specific route is not leaked.

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.

✓
The summary route 10.0.0.0/8 is being installed in the global table, but the more specific route 10.1.1.0/24 is not leaked, causing traffic to be dropped.
Why this is correct
Correct: The summary lacks the specific route; traffic to 10.1.1.0/24 matches the summary but may be discarded if the summary points to null or is not resolved.
Related concept
CIDR notation defines the prefix length.
✗
The route-map should use match ip address prefix-list SPECIFIC instead of SUMMARY.
Why it's wrong here
Incorrect: The intent is to leak a summary, but the specific route also needs to be leaked or the summary must point to a valid next-hop.
✗
The VRF must have a default route to reach the global table.
Why it's wrong here
Incorrect: The issue is about leaking from VRF to global, not the other direction.
✗
The prefix-list should permit 10.1.1.0/24 only.
Why it's wrong here
Incorrect: The summary is intended, but it fails to provide reachability to the specific subnet.

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.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

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?

VRF-Lite — This question tests VRF-Lite — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The summary route 10.0.0.0/8 is being installed in the global table, but the more specific route 10.1.1.0/24 is not leaked, causing traffic to be dropped. — The summary route 10.0.0.0/8 covers the more specific subnet 10.1.1.0/24, but the route-map only leaks the summary, not the specific. When the global table has the summary, traffic to 10.1.1.0/24 is forwarded based on the summary, but since the specific route is not leaked, the packet may be dropped or sent to a null interface if the summary points to a discard. The issue is that the summary route does not provide reachability to the specific subnet because the specific route is not leaked.

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.

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