The answer is that a short IKE phase 1 lifetime of 3600 seconds can cause frequent reauthentication and potential service disruption. This is because IKE phase 1 establishes the secure, authenticated control channel used to negotiate subsequent IKE phase 2 security associations; a one-hour lifetime forces both VPN peers to re-authenticate and re-establish this channel every hour, and if the rekeying process fails due to transient network issues or resource exhaustion, active tunnels can drop and impact production traffic. On the CISSP exam, this tests your understanding of the trade-off between security and availability in cryptographic protocol design—a common trap is assuming shorter lifetimes are always better for security, when in fact they can degrade availability. For a memory tip, think of IKE phase 1 as the "master lock" on a secure door: changing it too often risks jamming the mechanism, so balance is key.
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. 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.
Exhibit
Refer to the exhibit. The following output is from a Cisco router:
crypto isakmp policy 10
hash sha256
authentication pre-share
group 14
lifetime 3600
A security engineer notices that the IKE phase 1 lifetime is set to 3600 seconds. What is a potential security implication?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Short lifetimes may cause frequent reauthentication and potential disruption
IKE phase 1 establishes a secure authenticated channel for subsequent IKE phase 2 negotiations. A lifetime of 3600 seconds (1 hour) is relatively short, causing frequent reauthentication. This can lead to service disruption if the rekeying process fails or if the VPN peers experience transient network issues, potentially dropping active tunnels and impacting production traffic.
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.
✗
Longer lifetimes reduce rekeying overhead
Why it's wrong here
This is true, but the question asks about a security implication of the short lifetime.
✗
Shorter lifetimes increase performance
Why it's wrong here
Shorter lifetimes increase CPU usage due to frequent rekeying.
✓
Short lifetimes may cause frequent reauthentication and potential disruption
Why this is correct
Frequent rekeying increases overhead and risk of disruption if rekey fails.
Related concept
Read the scenario before looking for a memorised answer.
✗
The lifetime should be at least 86400 seconds
Why it's wrong here
There is no mandatory minimum; 3600 seconds is acceptable but more frequent.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the trade-off between security and availability: candidates may incorrectly assume shorter lifetimes are always more secure without considering the operational risk of frequent reauthentication causing tunnel drops.
Detailed technical explanation
How to think about this question
IKE phase 1 uses either Main Mode or Aggressive Mode to establish an ISAKMP SA, with authentication methods like pre-shared keys or certificates. The lifetime is negotiated during this phase; if peers have mismatched lifetimes, the shorter one is used. In real-world scenarios, a 3600-second lifetime on a busy VPNgateway can cause all tunnels to rekey simultaneously, leading to a thundering herd problem that overwhelms the CPU and causes temporary connectivity loss.
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: Short lifetimes may cause frequent reauthentication and potential disruption — IKE phase 1 establishes a secure authenticated channel for subsequent IKE phase 2 negotiations. A lifetime of 3600 seconds (1 hour) is relatively short, causing frequent reauthentication. This can lead to service disruption if the rekeying process fails or if the VPN peers experience transient network issues, potentially dropping active tunnels and impacting production traffic.
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.
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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