PCNSE Practice Question: Managing Troubleshooting and High Availability
An HA pair is configured with active/active mode and session sync enabled. After a failover, a network administrator notices that some new TCP connections fail. The firewall logs show no drops. What is the most likely issue?
⚠ Common exam trap
Watch out — candidates often assume session sync covers all TCP packets, including the initial handshake, but in reality, session sync only replicates established sessions, not half-open ones, making asymmetric routing during the handshake a critical failure point.
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
✓
Asymmetric routing is causing the SYN packet to be processed by one firewall and the SYN-ACK by the other
In an active/active HA pair with session sync enabled, asymmetric routing can occur after a failover if the traffic flow changes such that the SYN packet is processed by one firewall and the SYN-ACK by the other. Since session sync only synchronizes established sessions, not half-open ones, the firewall receiving the SYN-ACK does not have a session entry for the SYN, causing it to drop the SYN-ACK as a non-SYN packet without a session. The firewall logs show no drops because the drop occurs at the session lookup stage and may not be logged by default, or the drop counter is not incremented for this specific scenario.
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 ARP cache on the firewalls is stale
Why it's wrong here
ARP would cause drops, not connection failures.
- ✗
Flow-based routing is misconfigured
Why it's wrong here
Flow-based routing is not a feature; policy-based routing is.
- ✗
Session synchronization is not functioning for TCP
Why it's wrong here
Session sync is enabled and TCP is synced.
- ✓
Asymmetric routing is causing the SYN packet to be processed by one firewall and the SYN-ACK by the other
Why this is correct
Active/active requires careful design to ensure symmetric traffic flows.
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.