PCNE Practice Question: Managing, Monitoring, and Optimising Network Operations
A network engineer notices asymmetric routing between two VPCs connected via VPC peering. Traffic from VPC A to VPC B flows correctly, but return traffic from VPC B to VPC A drops. What is the most likely cause?
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
✓
Overlapping CIDR ranges in the peered VPCs
Asymmetric routing in VPC peering often occurs when VPCs have overlapping CIDR ranges or when one VPC has a default route that points to another peering, causing the return traffic to take a different path that may be blocked by firewall rules or not have a route.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
MTU mismatch between VPCs
Why it's wrong here
MTU mismatch causes fragmentation but not asymmetric routing.
- ✗
BGP session flaps on Cloud Router
Why it's wrong here
BGP flaps affect dynamic routes, but VPC peering uses static routes, not BGP.
- ✓
Overlapping CIDR ranges in the peered VPCs
Why this is correct
Overlapping CIDRs can cause asymmetric routing because a more specific route may not be present, leading to different paths.
- ✗
Firewall rules blocking ICMP
Why it's wrong here
ICMP blocking would drop ping but not necessarily asymmetric routing of TCP traffic.
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 PCNE practice question is part of Courseiva's free Google Cloud 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 PCNE exam.