CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. 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.
Exhibit
Refer to the exhibit.
$$$ START CONFIG
crypto isakmp policy 10
encryption aes 256
hash sha256
authentication pre-share
group 14
lifetime 86400
crypto isakmp key cisco123 address 203.0.113.1
!
crypto ipsec transform-set TSET esp-aes 256 esp-sha256-hmac
!
crypto map CMAP 10 ipsec-isakmp
set peer 203.0.113.1
set transform-set TSET
match address 101
!
interface Tunnel0
ip address 10.0.0.1 255.255.255.252
tunnel source GigabitEthernet0/0
tunnel destination 203.0.113.1
crypto map CMAP
$$$ END CONFIG
Refer to the exhibit. The VPN tunnel is not coming up. What is the most likely configuration error?
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 crypto map is applied to the Tunnel interface instead of the physical interface.
The crypto map must be applied to the physical interface (e.g., GigabitEthernet0/0) that connects to the VPN peer, not to the Tunnel interface. The Tunnel interface is a logical construct used for overlay routing (e.g., GRE or IPsec VTI), but the crypto map defines the IPsec security associations on the actual egress interface. Applying it to the Tunnel interface prevents the IPsec process from matching outbound traffic to the correct physical path, so the tunnel never establishes.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 encryption algorithm AES 256 is not supported.
Why it's wrong here
AES 256 is commonly supported.
✓
The crypto map is applied to the Tunnel interface instead of the physical interface.
Why this is correct
Crypto map must be applied to the physical interface that connects to the peer.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The hash algorithm SHA256 is not supported.
Why it's wrong here
SHA256 is supported.
✗
The Diffie-Hellman group 14 is not strong enough.
Why it's wrong here
Group 14 is acceptable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the misconception that the crypto map should be applied to the Tunnel interface (since it 'protects' the tunnel), but the correct placement is always on the physical egress interface where the IPsec packets actually leave the router.
Detailed technical explanation
How to think about this question
In Cisco IOS, the crypto map is applied to the physical interface using the `crypto map <map-name>` command under interface configuration mode. The IPsec process inspects outbound packets on that physical interface and applies encryption based on the crypto map entries. If the crypto map is applied to a Tunnel interface (e.g., for a GRE-over-IPsec topology), the IPsec engine never sees the actual outbound traffic because the Tunnel interface encapsulates packets before they reach the physical interface, breaking the SA negotiation. This is a common misconfiguration when combining tunneling protocols with IPsec.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The crypto map is applied to the Tunnel interface instead of the physical interface. — The crypto map must be applied to the physical interface (e.g., GigabitEthernet0/0) that connects to the VPN peer, not to the Tunnel interface. The Tunnel interface is a logical construct used for overlay routing (e.g., GRE or IPsec VTI), but the crypto map defines the IPsec security associations on the actual egress interface. Applying it to the Tunnel interface prevents the IPsec process from matching outbound traffic to the correct physical path, so the tunnel never establishes.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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