Quick Answer
The answer is that the EDL cache time is set higher than the refresh interval. This occurs because the firewall’s cache time dictates how long it holds a downloaded list before requesting a fresh copy from the server; if the cache time is configured to 10 minutes while the server updates every 5 minutes, the firewall will not poll for the new list until its local cache expires, causing it to serve stale data. On the Palo Alto Networks PCNSA exam, this scenario tests your understanding of how External Dynamic List (EDL) cache time and refresh intervals interact—a common trap is assuming the firewall checks the server at the same rate the server updates, when in reality the cache time overrides that frequency. A helpful memory tip is to think of the cache time as a “stale buffer”: if it’s longer than the server’s update cycle, the firewall is always one refresh behind.
This PCNSA practice question tests your understanding of managing objects. 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.
An organization uses an External Dynamic List (EDL) to block IP addresses. The EDL is updated every 5 minutes on the server, but the firewall still uses the old list even after the refresh interval. What is the most likely cause?
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.
The EDL URL is invalid
Why wrong: An invalid URL would prevent retrieval entirely.
The EDL is not registered as a dynamic list
Why wrong: If not registered, the firewall would not attempt to retrieve it.
The firewall's DNS resolution fails
Why wrong: DNS failure would cause an error, not stale data.
The EDL cache time is set higher than the refresh interval
The cache time instructs the firewall to keep the old list until it expires.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The EDL cache time is set higher than the refresh interval
The External Dynamic List (EDL) cache time on the firewall determines how long the firewall retains the downloaded list before requesting a fresh copy from the server. If the cache time is set higher than the server's update interval (e.g., 10 minutes vs. 5 minutes), the firewall will continue using the old list even after the server has updated, because it does not re-fetch the list until the cache expires. This is the most likely cause of the observed behavior.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
The EDL URL is invalid
Why it's wrong here
An invalid URL would prevent retrieval entirely.
The EDL is not registered as a dynamic list
Why it's wrong here
If not registered, the firewall would not attempt to retrieve it.
The firewall's DNS resolution fails
Why it's wrong here
DNS failure would cause an error, not stale data.
The EDL cache time is set higher than the refresh interval
Why this is correct
The cache time instructs the firewall to keep the old list until it expires.
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.
Common exam traps
The trap here is that candidates often assume the issue is with connectivity or registration (options A, B, or C), but the real cause is a misalignment between the firewall's cache time and the server's update frequency, which is a subtle but critical configuration detail.
Detailed technical explanation
The firewall's EDL cache time is configured in minutes and controls the Time-To-Live (TTL) for the downloaded list. When the cache time expires, the firewall sends an HTTP GET request to the EDL URL and compares the response's Last-Modified header or ETag to determine if the list has changed. If the cache time is longer than the server's update interval, the firewall will skip the refresh even though the server has new data, leading to stale IP addresses being used for policy enforcement. This is a common misconfiguration in environments where the EDL is updated frequently (e.g., threat intelligence feeds).
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the PCNSA 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.
What to study next
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FAQ
Managing Objects — This question tests Managing Objects — Read the scenario before looking for a memorised answer..
The correct answer is: The EDL cache time is set higher than the refresh interval — The External Dynamic List (EDL) cache time on the firewall determines how long the firewall retains the downloaded list before requesting a fresh copy from the server. If the cache time is set higher than the server's update interval (e.g., 10 minutes vs. 5 minutes), the firewall will continue using the old list even after the server has updated, because it does not re-fetch the list until the cache expires. This is the most likely cause of the observed behavior.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
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Variation 1. An organization uses multiple firewalls and wants to share dynamic address groups across them. Which feature should be used?
hardWhy D: External Dynamic Lists (EDLs) allow dynamic address groups to be shared across multiple firewalls by referencing a common external source, such as a URL or file hosted on a web server. This enables consistent, real-time updates to address objects across the entire firewall fleet without manual intervention, making it the correct choice for sharing dynamic address groups.
Last reviewed: Jun 25, 2026
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