The answer is a missing access list to define the traffic selector. In GETVPN, the key server (KS) uses an access list to specify which traffic should be encrypted by the group members (GMs); without this traffic selector, the KS cannot push the encryption policy to the GMs, so traffic between them remains unencrypted even though registration succeeds. On the ENCOR 350-401 exam, this concept tests your understanding that GETVPN relies on a centralized policy definition—the KS defines the “interesting traffic” via an access list, and GMs simply apply it. A common trap is assuming the transform set or group name alone is sufficient, but the access list is the critical missing piece that triggers encryption. Memory tip: “No ACL, no encrypt—GETVPN needs a traffic selector to protect.”
CCNP VPN Technologies Practice Question
This 350-401 practice question tests your understanding of vpn technologies. 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.
A network engineer is configuring a GETVPN solution for a large enterprise with many remote sites. The engineer wants to ensure that all traffic between sites is encrypted using a common group key. The key server (KS) is a Cisco ASR 1000. After configuration, the group members (GMs) can register with the KS, but traffic between GMs is not encrypted. The engineer checks the KS configuration and sees that the crypto gdoi group has been defined with a transform set and a security association. What is the most likely missing configuration?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The KS is missing an access list to define the traffic to encrypt.
In GETVPN, the KS must define a traffic selector (access list) that specifies which traffic to encrypt. Without a proper access list, the KS will not send the policy to the GMs, and traffic will pass in the clear. Option A is correct because the access list is missing. Option B is incorrect because the group name is not the issue. Option C is incorrect because the KS does not need an IPsec profile. Option D is incorrect because GMs can be in different subnets.
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 KS is missing an access list to define the traffic to encrypt.
Why this is correct
Correct because the traffic selector is required for GETVPN policy.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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 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 350-401 subnetting questions on CIDR, address ranges, and subnet selection.
VPN Technologies — This question tests VPN Technologies — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The KS is missing an access list to define the traffic to encrypt. — In GETVPN, the KS must define a traffic selector (access list) that specifies which traffic to encrypt. Without a proper access list, the KS will not send the policy to the GMs, and traffic will pass in the clear. Option A is correct because the access list is missing. Option B is incorrect because the group name is not the issue. Option C is incorrect because the KS does not need an IPsec profile. Option D is incorrect because GMs can be in different subnets.
What should I do if I get this 350-401 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 350-401 subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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