The answer is that the new route's destination range is not set to 0.0.0.0/0. In Google Cloud, a custom route can only override the default internet gateway route if it matches the same destination prefix, because route priority only applies when two routes have identical destination ranges. Since the default route already covers all egress traffic with a destination of 0.0.0.0/0, a new route with a different destination range—even with a higher priority (lower numerical value)—will not match general internet-bound traffic, leaving the default route as the active path. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of VPC route matching logic and the common trap of assuming priority alone dictates behavior; the exam often presents a custom route with a specific CIDR block like 10.0.0.0/8, which will only redirect traffic to that subnet, not all egress. A useful memory tip: "Priority picks the winner, but only if the destination is a twin."
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 has a VPC network with a default route to the internet gateway. They want all egress traffic to go through a firewall appliance instead. They create a new route with a next hop to the appliance and a priority of 500. However, traffic is still going through the internet gateway. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The new route's destination range is not 0.0.0.0/0
The default route to the internet gateway has a destination of 0.0.0.0/0. For the new route to override it, the new route must also have a destination of 0.0.0.0/0 (or a more specific prefix). If the new route's destination range is not 0.0.0.0/0, it will not match all egress traffic, and the existing default route with a lower priority (higher numerical value) will still be used for traffic that does not match the new route's destination.
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.
✗
The new route has a higher tag specification that overrides
Why it's wrong here
Tags are optional; if the new route has no tags, it applies to all instances. The default route has no tags, so no conflict.
✓
The new route's destination range is not 0.0.0.0/0
Why this is correct
The default route covers all destinations; the new route must also be 0.0.0.0/0 with a higher priority to override.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The appliance does not have IP forwarding enabled
Why it's wrong here
IP forwarding is needed for the appliance to forward traffic, but if the route is not applied, it doesn't matter.
✗
The firewall appliance is in a different network
Why it's wrong here
Routes are intra-VPC; if the appliance is in the same VPC, it works.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that a lower priority number always overrides a higher priority number, but the trap here is that the route must also have the same destination prefix (0.0.0.0/0) to override the default route; otherwise, the default route remains active for all unmatched traffic.
Detailed technical explanation
How to think about this question
In Google Cloud VPC (and similar cloud networking), route selection is based on the longest prefix match; if two routes have the same destination prefix, the route with the lower priority (numerical value) wins. The default route 0.0.0.0/0 with priority 1000 (or similar) will always be used for all egress traffic unless a more specific route (e.g., 0.0.0.0/0 with a lower priority) or a route with a more specific destination prefix exists. A route with destination 10.0.0.0/8 would only match traffic to that range, not all egress traffic.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Configuring network security — This question tests Configuring network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The new route's destination range is not 0.0.0.0/0 — The default route to the internet gateway has a destination of 0.0.0.0/0. For the new route to override it, the new route must also have a destination of 0.0.0.0/0 (or a more specific prefix). If the new route's destination range is not 0.0.0.0/0, it will not match all egress traffic, and the existing default route with a lower priority (higher numerical value) will still be used for traffic that does not match the new route's destination.
What should I do if I get this PCSE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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