easyMultiple ChoiceObjective-mapped
CISSP Practice Question: Notices that the IKE phase 1 lifetime is set to…
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?
⚠ Common exam trap
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.
Answer choices
Why each option matters
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.
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
While it is true that longer IKE Phase 1 lifetimes reduce the frequency of rekeying, thereby lowering CPU and network overhead, this statement does not address the specific security implication of a *short* lifetime. The question seeks to identify a negative consequence or risk associated with a short lifetime, not a general benefit of a long one. Therefore, while factually correct, it fails to answer the prompt's core inquiry about the implications of a short lifetime.
- ✗
Shorter lifetimes increase performance
Why it's wrong here
Shorter IKE Phase 1 lifetimes actually decrease, rather than increase, performance due to the heightened computational demands of frequent rekeying. Each rekeying event requires significant CPU cycles for cryptographic operations, including Diffie-Hellman key exchanges and hashing. Consequently, a short lifetime leads to more frequent re-establishment of the Phase 1 Security Association, consuming more resources and potentially introducing latency and reducing overall throughput.
- ✓
Short lifetimes may cause frequent reauthentication and potential disruption
Why this is correct
Short IKE Phase 1 lifetimes necessitate frequent reauthentication, which significantly increases the operational overhead and the potential for service disruption. Each rekeying attempt presents an opportunity for failure due to network issues, misconfigurations, or resource exhaustion on either endpoint. Such frequent re-establishment of the secure channel can lead to intermittent connectivity problems or complete outages if the reauthentication process repeatedly fails, impacting availability and user experience.
- ✗
The lifetime should be at least 86400 seconds
Why it's wrong here
There is no universally mandated minimum lifetime for IKE Phase 1 Security Associations, such as 86400 seconds (24 hours). The optimal lifetime is a policy decision based on an organization's specific security requirements, risk tolerance, and network environment. While longer lifetimes reduce overhead, shorter ones enhance forward secrecy, making the choice a balance between security posture and operational efficiency, not adherence to an arbitrary minimum value.
Go deeper
Related to this question
Learn chapter
Security Governance and Principles
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
Key term
VPN
A VPN (Virtual Private Network) creates a secure, encrypted tunnel between your device and a remote server, protecting your data and hiding your online activity.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.