This 300-410 practice question tests your understanding of ipsec site-to-site vpn. 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 runs the following command to troubleshoot an IPsec Site-to-Site VPN issue:
R1# show crypto ipsec transform-set
Transform set combined-des-sha: { esp-des esp-sha-hmac }
will negotiate = { Tunnel, },
Transform set myset: { esp-3des esp-sha-hmac }
will negotiate = { Tunnel, },
Transform set strong: { esp-aes 256 esp-sha-hmac }
will negotiate = { Tunnel, },
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The transform set 'combined-des-sha' uses DES, which is not recommended due to security vulnerabilities.
The output shows three transform sets, including 'combined-des-sha', which uses DES (Data Encryption Standard) with a 56-bit key. DES is considered cryptographically weak and has been deprecated due to known vulnerabilities, such as susceptibility to brute-force attacks. Cisco recommends using AES or 3DES as a minimum for production IPsec VPNs, making option B correct.
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.
✗
All transform sets are using strong encryption and are acceptable for production.
Why it's wrong here
DES is considered weak and should not be used.
✓
The transform set 'combined-des-sha' uses DES, which is not recommended due to security vulnerabilities.
Why this is correct
DES is deprecated and insecure; AES should be used instead.
Related concept
Read the scenario before looking for a memorised answer.
✗
The transform sets are not configured correctly because they do not specify the mode.
Why it's wrong here
The mode is shown as Tunnel, which is correct for site-to-site VPN.
✗
The transform set 'strong' is not supported because it uses AES 256.
Why it's wrong here
AES 256 is supported and recommended.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the candidate's awareness of deprecated or weak cryptographic algorithms (like DES) versus strong ones (like AES), and the trap here is assuming that all listed transform sets are equally valid or that the missing mode keyword indicates a misconfiguration.
Trap categories for this question
Command / output trap
The mode is shown as Tunnel, which is correct for site-to-site VPN.
Detailed technical explanation
How to think about this question
DES (56-bit key) can be broken in under 24 hours with modern hardware, which is why it is deprecated in favor of AES (128/256-bit) or 3DES (168-bit effective). The 'show crypto ipsec transform-set' command displays the configured transform sets and their negotiated mode; the absence of a mode keyword in the output simply means the default 'tunnel' mode is used, not that the configuration is incomplete. In real-world scenarios, using DES in a Site-to-Site VPN could expose sensitive data to interception, especially over untrusted networks like the internet.
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 practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
IPsec Site-to-Site VPN — This question tests IPsec Site-to-Site VPN — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The transform set 'combined-des-sha' uses DES, which is not recommended due to security vulnerabilities. — The output shows three transform sets, including 'combined-des-sha', which uses DES (Data Encryption Standard) with a 56-bit key. DES is considered cryptographically weak and has been deprecated due to known vulnerabilities, such as susceptibility to brute-force attacks. Cisco recommends using AES or 3DES as a minimum for production IPsec VPNs, making option B correct.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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