- A
Enable Client Certificate Validation on the HTTPS backend service and configure the backend to read the X-Forwarded-Client-Cert header.
This is the correct method for mTLS with the HTTPS load balancer.
- B
Use an SSL policy with mTLS and set the backend service to require client certificates.
Why wrong: SSL policies are for server TLS, not client certificate validation.
- C
Use Cloud Armor with mTLS and configure a custom request header to include the client certificate.
Why wrong: Cloud Armor does not support client certificate validation natively.
- D
Configure the GKE Ingress to use an SSL certificate and set the annotation for client certificate validation.
Why wrong: GKE Ingress annotations for client certificates are not supported by the standard HTTPS load balancer.
Quick Answer
The correct answer is to enable Client Certificate Validation on the HTTPS backend service and configure the backend to read the X-Forwarded-Client-Cert (XFCC) header. This works because Google Cloud’s external HTTPS load balancer terminates TLS, validates the client certificate at the edge, and then injects the certificate details into the XFCC header, passing the client’s identity to the backend without requiring the GKE Ingress or application to handle certificate logic. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how mTLS is offloaded to the load balancer rather than implemented within the cluster, a common trap being confusion with GKE-native mTLS or Istio. Remember that the load balancer acts as the TLS terminator and identity proxy, not the backend. A useful memory tip: think “XFCC = eXternal Forwarded Client Cert” — the load balancer validates, then forwards the cert details in the header.
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 deploys a web application on Google Kubernetes Engine (GKE) with an Ingress resource handled by an external HTTPS load balancer. They want to enforce mutual TLS (mTLS) authentication where the load balancer verifies the client certificate and then passes the client's identity to the backend using a header. Which configuration should be used?
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
Enable Client Certificate Validation on the HTTPS backend service and configure the backend to read the X-Forwarded-Client-Cert header.
Option A is correct because Google Cloud's external HTTPS load balancer supports mTLS by enabling Client Certificate Validation on the backend service. When enabled, the load balancer terminates TLS, validates the client certificate, and injects the client certificate details into the X-Forwarded-Client-Cert (XFCC) header, which the backend application can read to identify the client. This approach offloads certificate validation to the load balancer and passes identity via a standard header, meeting the requirement without modifying the GKE Ingress or backend application logic.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable Client Certificate Validation on the HTTPS backend service and configure the backend to read the X-Forwarded-Client-Cert header.
Why this is correct
This is the correct method for mTLS with the HTTPS load balancer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use an SSL policy with mTLS and set the backend service to require client certificates.
Why it's wrong here
SSL policies are for server TLS, not client certificate validation.
- ✗
Use Cloud Armor with mTLS and configure a custom request header to include the client certificate.
Why it's wrong here
Cloud Armor does not support client certificate validation natively.
- ✗
Configure the GKE Ingress to use an SSL certificate and set the annotation for client certificate validation.
Why it's wrong here
GKE Ingress annotations for client certificates are not supported by the standard HTTPS load balancer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that mTLS can be configured directly on the Ingress resource or via SSL policies, when in fact it requires enabling Client Certificate Validation on the backend service and using the XFCC header to pass client identity.
Detailed technical explanation
How to think about this question
The X-Forwarded-Client-Cert (XFCC) header is defined in RFC 7239 and carries the client certificate in a URI-encoded PEM format. When Client Certificate Validation is enabled on the backend service, the load balancer performs full certificate chain validation and only forwards the request if the certificate is valid; the backend can then parse the XFCC header to extract fields like Subject, Issuer, and Serial Number. In a real-world scenario, this is critical for zero-trust architectures where the backend must authenticate the client without re-negotiating TLS, reducing latency and complexity.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable Client Certificate Validation on the HTTPS backend service and configure the backend to read the X-Forwarded-Client-Cert header. — Option A is correct because Google Cloud's external HTTPS load balancer supports mTLS by enabling Client Certificate Validation on the backend service. When enabled, the load balancer terminates TLS, validates the client certificate, and injects the client certificate details into the X-Forwarded-Client-Cert (XFCC) header, which the backend application can read to identify the client. This approach offloads certificate validation to the load balancer and passes identity via a standard header, meeting the requirement without modifying the GKE Ingress or backend application logic.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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