- A
Shielded VMs with Secure Boot enabled
Why wrong: Shielded VMs protect against boot-level attacks using TPM and Secure Boot — they don't encrypt network traffic between VMs.
- B
VPC firewall rules denying all non-encrypted traffic
Why wrong: VPC firewall rules control whether traffic is allowed or denied based on port/protocol/IP — they can't inspect or enforce encryption of allowed traffic.
- C
Mutual TLS (mTLS) enforced at the application layer between VMs
GCP's VPC doesn't automatically encrypt VM-to-VM traffic. mTLS at the application layer (using certificate-based authentication) is the standard method to enforce encrypted communication between services.
- D
Enabling VPC Flow Logs on all subnets
Why wrong: VPC Flow Logs capture traffic metadata for analysis — they don't encrypt traffic.
How to Enforce Encryption in Transit for All VM-to-VM Traffic in GCP
This ACE practice question tests your understanding of mutual tls (mtls). The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: mutual TLS (mTLS). 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 compliance requirement mandates that all VM-to-VM traffic within a GCP project must be encrypted in transit, even for internal VPC traffic. Which feature enforces this for Compute Engine?
Quick Answer
The answer is Mutual TLS (mTLS) enforced at the application layer between VMs. This is the correct choice because mTLS, when enabled on a GCP VPC network, automatically encrypts all VM-to-VM traffic in transit using TLS 1.2 or higher, requiring both sides to present certificates for mutual authentication, which satisfies compliance mandates for encrypting internal VPC traffic without any application-level changes. On the Google Associate Cloud Engineer exam, this question tests your understanding of GCP’s internal mTLS feature as a network-level encryption solution, often appearing as a trap where candidates mistakenly choose VPC firewall rules or Cloud VPN, which do not enforce encryption between internal VMs. A key memory tip: think “mutual handshake” — both VMs must prove identity with certificates before any encrypted data flows, ensuring no plaintext traffic ever passes within the VPC.
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
Mutual TLS (mTLS) enforced at the application layer between VMs
Mutual TLS (mTLS) enforced at the application layer is the correct answer. mTLS requires both client and server to present certificates and establishes a TLS-encrypted session between applications, ensuring encryption in transit for VM-to-VM traffic. In GCP, mTLS must be implemented within the application code or via a service mesh, not as a VPC-level feature. The other options are incorrect: Shielded VMs with Secure Boot protect boot integrity but do not encrypt traffic; VPC firewall rules filter traffic based on IP/port but cannot enforce encryption of the payload; VPC Flow Logs provide network monitoring but no encryption.
Key principle: Mutual TLS (mTLS)
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Shielded VMs with Secure Boot enabled
Why it's wrong here
Shielded VMs protect against boot-level attacks using TPM and Secure Boot — they don't encrypt network traffic between VMs.
- ✗
VPC firewall rules denying all non-encrypted traffic
Why it's wrong here
VPC firewall rules control whether traffic is allowed or denied based on port/protocol/IP — they can't inspect or enforce encryption of allowed traffic.
- ✓
Mutual TLS (mTLS) enforced at the application layer between VMs
- ✗
Enabling VPC Flow Logs on all subnets
Why it's wrong here
VPC Flow Logs capture traffic metadata for analysis — they don't encrypt traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often assume GCP offers a built-in VPC-level feature for automatic encryption of internal VM-to-VM traffic, but no such option exists. Instead, encryption must be implemented at the application layer using mTLS, IPsec tunnels, or similar methods. Firewall rules cannot enforce encryption, only permit or deny traffic.
Detailed technical explanation
How to think about this question
GCP's internal mTLS works by leveraging the Identity and Access Management (IAM) system to issue short-lived certificates to each VM instance, which are then used to establish TLS sessions between VMs on the same VPC network. This encryption is transparent to applications and operates at the network layer, using the gRPC-based Google Network Connectivity Center (NCC) or the internal load balancer infrastructure to enforce encryption without requiring application-layer TLS configuration. In a real-world scenario, if a compliance auditor requires encryption for all east-west traffic (e.g., PCI DSS), enabling internal mTLS ensures that even legacy applications using unencrypted protocols like HTTP or MySQL are automatically encrypted in transit.
KKey Concepts to Remember
- Mutual TLS (mTLS)
- Encryption in transit
- VPC firewall rules
- Application-layer encryption
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Mutual TLS (mTLS)
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Visual reference
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
What to study next
Got this wrong? Here's your next step.
Review mutual TLS (mTLS), then practise related ACE questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this ACE question test?
Mutual TLS (mTLS)
What is the correct answer to this question?
The correct answer is: Mutual TLS (mTLS) enforced at the application layer between VMs — Mutual TLS (mTLS) enforced at the application layer is the correct answer. mTLS requires both client and server to present certificates and establishes a TLS-encrypted session between applications, ensuring encryption in transit for VM-to-VM traffic. In GCP, mTLS must be implemented within the application code or via a service mesh, not as a VPC-level feature. The other options are incorrect: Shielded VMs with Secure Boot protect boot integrity but do not encrypt traffic; VPC firewall rules filter traffic based on IP/port but cannot enforce encryption of the payload; VPC Flow Logs provide network monitoring but no encryption.
What should I do if I get this ACE question wrong?
Review mutual TLS (mTLS), then practise related ACE questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Mutual TLS (mTLS)
About these practice questions
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Last reviewed: Jun 30, 2026
This ACE 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 ACE exam.
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