The answer is that IKEv2 can authenticate using EAP and it uses UDP port 500 for initial IKE SA establishment with port 4500 for NAT traversal. These are correct because IKEv2, defined in RFC 7296, was designed with built-in support for EAP to allow advanced authentication methods like certificates or pre-shared keys, while the dual UDP port system ensures IPsec traffic survives NAT devices by encapsulating packets in UDP when a NAT is detected. On the Cisco CCNP ENARSI 300-410 exam, this question tests your understanding of IKEv2’s enhanced flexibility over IKEv1, often appearing as a trap where candidates confuse IKEv2’s mandatory NAT traversal with IKEv1’s optional NAT-T. A common memory tip: remember “500 for start, 4500 for smart” — IKEv2 starts on port 500, then smartly switches to 4500 when NAT is in the path.
300-410 IPsec Site-to-Site VPN Practice Question
This 300-410 practice question tests your understanding of ipsec site-to-site vpn. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 correctly describe the use of IKEv2 for IPsec site-to-site VPNs? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
IKEv2 uses UDP port 500 and 4500 for NAT traversal.
Option A is correct because IKEv2 uses UDP port 500 for initial IKE SA establishment and port 4500 for NAT traversal (encapsulating IPsec packets in UDP to pass through NAT devices). This is a standard behavior defined in RFC 7296, ensuring compatibility with NAT environments.
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.
✓
IKEv2 uses UDP port 500 and 4500 for NAT traversal.
Why this is correct
Correct. IKEv2 uses UDP 500 for initial exchanges and UDP 4500 when NAT is detected.
Related concept
Read the scenario before looking for a memorised answer.
✗
IKEv2 supports only pre-shared keys for authentication.
Why it's wrong here
Incorrect. IKEv2 supports pre-shared keys, digital certificates, and EAP.
✗
IKEv2 uses aggressive mode to establish the IKE SA.
Why it's wrong here
Incorrect. Aggressive mode is a feature of IKEv1; IKEv2 uses a different exchange mechanism.
✓
IKEv2 can authenticate using EAP (Extensible Authentication Protocol).
Why this is correct
Correct. IKEv2 supports EAP, which allows integration with authentication servers like RADIUS.
Related concept
Read the scenario before looking for a memorised answer.
✗
The default IKEv2 SA lifetime is 3600 seconds.
Why it's wrong here
Incorrect. The default IKEv2 SA lifetime is 86400 seconds (24 hours).
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that IKEv2 uses aggressive mode (like IKEv1) or that its default SA lifetime is 3600 seconds, when in fact IKEv2 uses a simpler exchange and a 24-hour default lifetime.
Detailed technical explanation
How to think about this question
IKEv2's use of UDP port 4500 for NAT traversal involves encapsulating ESP packets in UDP headers to avoid NAT issues, and it also supports MOBIKE (RFC 4555) for dynamic IP address changes. In real-world deployments, this allows VPNs to survive WAN failovers or mobile client IP changes without re-establishing the entire IKE SA. Additionally, EAP authentication in IKEv2 enables integration with AAA servers like RADIUS for certificate-less user authentication.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: IKEv2 uses UDP port 500 and 4500 for NAT traversal. — Option A is correct because IKEv2 uses UDP port 500 for initial IKE SA establishment and port 4500 for NAT traversal (encapsulating IPsec packets in UDP to pass through NAT devices). This is a standard behavior defined in RFC 7296, ensuring compatibility with NAT environments.
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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