PCNSE Decryption and SSL Inspection Practice Question
You are a network security engineer at a multinational corporation. The company has a main data center and three branch offices connected via MPLS. The firewall at the data center is a PA-5250 running PAN-OS 10.2. The firewall is configured for SSL Forward Proxy decryption of all outbound HTTPS traffic from internal users to the internet. Recently, users in Branch Office A report that they cannot access several external HTTPS websites, while users at other branches and the data center have no issues. The decryption policy for Branch Office A is identical to the others. You check the decryption statistics and see that for Branch Office A, the number of 'SSL handshake failures' is high. You also notice that the firewall's system log shows errors like 'peer certificate chain validation failure' for sessions from Branch Office A. The firewall has a forward trust certificate issued by an internal CA, and the internal CA certificate is installed on all clients. What is the most likely cause of this issue?
⚠ Common exam trap
The trap here is that candidates often blame certificate trust or decryption profile misconfigurations first, overlooking that asymmetric routing is a common network-layer cause of SSL decryption failures even when all security policies and certificates are correctly configured.
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
✓
Traffic from Branch Office A is asymmetrically routed, causing the TLS handshake to be incomplete.
C is correct because asymmetric routing causes the firewall to see only one side of the TCP handshake, preventing it from completing the TLS handshake. When traffic from Branch Office A takes a different return path (e.g., via another MPLS link or direct internet breakout), the firewall cannot associate the server's SYN-ACK with the original client SYN, leading to SSL handshake failures and 'peer certificate chain validation failure' errors in the logs. The decryption policy and certificates are identical across branches, so the issue is specific to the network path.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The forward trust certificate has expired or is not trusted by the clients in Branch Office A.
Why it's wrong here
Certificate expiration or trust issues would affect all users, not just Branch Office A, and would typically result in certificate warnings, not handshake failures.
- ✗
The decryption profile for Branch Office A is configured with an incorrect cipher suite that is not supported by the external websites.
Why it's wrong here
Incorrect cipher suites would cause different errors, and the profile is identical to working branches.
- ✓
Traffic from Branch Office A is asymmetrically routed, causing the TLS handshake to be incomplete.
Why this is correct
Asymmetric routing can cause the firewall to see only one side of the TCP handshake, leading to SSL handshake failures.
- ✗
The decryption policy rule for Branch Office A is missing the 'ssl-decrypt' action.
Why it's wrong here
The policy is identical to others that work, so this is unlikely.
Visual reference
Quick reference
Asymmetric Encryption Algorithm Comparison
| Algorithm | Key Exchange | Signatures | Equivalent Security Key | Notes |
|---|---|---|---|---|
| RSA-3072 | Yes | Yes | 128-bit | Widely deployed; slow for bulk data |
| ECDSA P-256 | No | Yes | 128-bit | Fast signatures; standard TLS certs |
| ECDH / ECDHE | Yes | No | 128-bit | Perfect forward secrecy in TLS 1.3 |
| DH / DHE | Yes | No | 128-bit (3072-bit key) | Replaced by ECDHE in modern TLS |
| Ed25519 | No | Yes | ~128-bit | SSH keys, modern PKI |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.