This PCNSE practice question tests your understanding of troubleshoot. 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 company with multiple branch offices connects to headquarters using IPSec VPN tunnels terminated on PA-220 firewalls. Users at one branch report intermittent connectivity issues when accessing critical applications hosted at HQ. Ping tests to HQ servers succeed consistently, but TCP-based applications (e.g., file transfers, web access) frequently drop connections after a few seconds, particularly when transferring large data. The VPN tunnel status shows 'active' with no rekeys. Security policies are configured to allow all required application traffic. Interface statistics show no discards or errors. Which action should be taken to resolve the issue?
Why wrong: Checksum offloading might cause corruption but not typical symptom of intermittent mid-transfer drops.
B
Change the IPSec encryption algorithm from AES-256 to AES-128.
Why wrong: Encryption algorithm does not affect packet size significantly and is unlikely to fix fragmentation.
C
Increase the TCP timeout value in the security policy.
Why wrong: Timeout would not cause failures mid-transfer but after idle periods.
D
Reduce the MTU on the branch firewall's WAN interface to 1400.
MTU mismatch across VPN can cause packet fragmentation and reassembly issues, leading to drops for large packets. Reducing MTU ensures packets fit within the tunnel.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Reduce the MTU on the branch firewall's WAN interface to 1400.
Option A is correct because the symptoms (TCP connections dropping mid-transfer, ping success) strongly suggest an MTU issue across the VPN tunnel. Reducing the MTU on the branch firewall's WAN interface to 1400 bytes often resolves fragmentation problems without disabling TCP MSS clamping. Option B is wrong because increasing TCP timeouts would delay disconnections but not prevent them; the drops are likely due to packet fragmentation. Option C is wrong because changing encryption algorithms does not significantly affect packet size and is unlikely to fix fragmentation. Option D is wrong because disabling TCP checksum offloading on clients might help if checksum offload were causing corruption, but the described symptoms point to MTU issues.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Disable TCP checksum offloading on the clients.
Why it's wrong here
Checksum offloading might cause corruption but not typical symptom of intermittent mid-transfer drops.
✗
Change the IPSec encryption algorithm from AES-256 to AES-128.
Why it's wrong here
Encryption algorithm does not affect packet size significantly and is unlikely to fix fragmentation.
✗
Increase the TCP timeout value in the security policy.
Why it's wrong here
Timeout would not cause failures mid-transfer but after idle periods.
✓
Reduce the MTU on the branch firewall's WAN interface to 1400.
Why this is correct
MTU mismatch across VPN can cause packet fragmentation and reassembly issues, leading to drops for large packets. Reducing MTU ensures packets fit within the tunnel.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNSE NAT questions on configuration and troubleshooting.
Troubleshoot — This question tests Troubleshoot — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Reduce the MTU on the branch firewall's WAN interface to 1400. — Option A is correct because the symptoms (TCP connections dropping mid-transfer, ping success) strongly suggest an MTU issue across the VPN tunnel. Reducing the MTU on the branch firewall's WAN interface to 1400 bytes often resolves fragmentation problems without disabling TCP MSS clamping. Option B is wrong because increasing TCP timeouts would delay disconnections but not prevent them; the drops are likely due to packet fragmentation. Option C is wrong because changing encryption algorithms does not significantly affect packet size and is unlikely to fix fragmentation. Option D is wrong because disabling TCP checksum offloading on clients might help if checksum offload were causing corruption, but the described symptoms point to MTU issues.
What should I do if I get this PCNSE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCNSE NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This PCNSE practice question is part of Courseiva's free Palo Alto Networks 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 PCNSE exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.