You decide to set up Cloud NAT. After completing the configuration, you find that one of your instances is not using the Cloud NAT for outbound NAT. What is the most likely cause of this problem?
A.
The instance has been configured with multiple interfaces.
B.
An external IP address has been configured on the instance.
C.
You have created static routes that use RFC1918 ranges.
D.
The instance is accessible by a load balancer external IP address.
The most likely cause of the problem is B. An external IP address has been configured on the instance. Cloud NAT is used for instances without external IP addresses. If the instance has an external IP, it will bypass Cloud NAT for outbound traffic.
B. An external IP address has been configured on the instance.
Explanation:
Cloud NAT and Instances: Cloud NAT is used for instances without external IP addresses that need to initiate outbound connections. If an instance has an external IP address, it may use that IP address for outbound connections instead of going through Cloud NAT.
Instance Configuration: If an external IP address is configured directly on the instance, the instance may use that IP address for outbound traffic, bypassing Cloud NAT.
To resolve the issue and ensure that the instance uses Cloud NAT for outbound NAT, you can either remove the external IP address from the instance or adjust the instance's routing configuration.
B is right The existence of an external IP address on an interface always takes precedence and always performs one-to-one NAT, without using Cloud NAT.
This is why https://cloud.google.com/nat/docs/overview#specifications
"The existence of an external IP address on an interface always takes precedence and always performs one-to-one NAT, without using Cloud NAT."
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