ANS-C01 Network Management and Operations Practice Question
A company is using AWS CloudFormation to deploy a VPC with public and private subnets, an internet gateway, and a NAT gateway. The deployment fails with the error: 'Route table rtb-12345678 already has a route with destination 0.0.0.0/0'. The network engineer reviews the template and sees that the public route table has a route to the internet gateway and the private route table has a route to the NAT gateway. Both route tables are defined in the same template. What is the most likely cause of this error?
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
✓
The public and private route tables are the same resource due to a typo in the template.
The error indicates that the same route table is being used for both routes, which happens when both resources reference the same route table ID. Option A is wrong because a route table can have multiple routes, but only one default route. Option C is wrong because the error is specific to duplicate routes, not a missing route. Option D is wrong because internet and NAT gateways can coexist in the same VPC.
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 internet gateway and NAT gateway cannot exist in the same VPC simultaneously.
Why it's wrong here
Incorrect: They can coexist; one is for public subnets, the other for private.
- ✓
The public and private route tables are the same resource due to a typo in the template.
Why this is correct
Correct: Using the same route table ID for both routes causes duplicate route error.
- ✗
The public route table already has a route to the internet gateway, and adding another default route is not allowed.
Why it's wrong here
Incorrect: A route table can have only one default route, but the error shows the same route table is being used.
- ✗
The NAT gateway route is missing a destination CIDR block.
Why it's wrong here
Incorrect: The error is about duplicate route, not missing destination.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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