Override Default Route for S3: Internet Gateway vs Direct Connect
A company has a Direct Connect connection with a private VIF to a VPC. The VPC has a virtual private gateway (VGW) attached. The on-premises network advertises a prefix 10.0.0.0/8 over BGP. The VPC has subnets with CIDR 10.0.1.0/24 and 10.0.2.0/24. The company wants to ensure that traffic to on-premises uses Direct Connect. However, traffic to an S3 bucket uses the internet. What route configuration is required?
Quick Answer
The correct answer is to add specific routes for S3 public IP prefixes pointing to the internet gateway. This works because of the longest prefix match rule in AWS route tables: a more specific route to the S3 prefixes (e.g., a /32 or a range from the S3 IP list) will override the general 10.0.0.0/8 route learned over Direct Connect via the virtual private gateway, forcing S3 traffic out to the internet instead. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how to selectively override default or BGP-advertised routes without breaking connectivity to on-premises networks. A common trap is assuming you can simply delete the Direct Connect route or change the VPC CIDR, but neither is valid—you must add explicit, more specific routes. Memory tip: think of it as "specific beats general"—the IGW route for S3 is the narrowest path, so it wins every time.
⚠ Common exam trap
The trap is assuming that a default route (0.0.0.0/0) to the internet gateway is sufficient, but that would also send all non-matching traffic (e.g., to the internet) via IGW, which might be undesirable. The correct approach is to add specific routes for S3 public IP prefixes to the IGW, leaving the propagated 10.0.0.0/8 route for on-premises traffic.
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
✓
Add specific routes for S3 public IP prefixes pointing to the internet gateway.
S3 public IP prefixes are not within the on-premises advertised prefix 10.0.0.0/8. Without explicit routes for S3, traffic to S3 would use the default route (if any) or be dropped. By adding specific routes for S3 public IP prefixes pointing to the internet gateway, S3 traffic is forced over the internet while all other traffic (including to on-premises) uses the Direct Connect private VIF via the propagated 10.0.0.0/8 route.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the VPC CIDR to avoid overlap with on-premises.
Why it's wrong here
Overlap is not the issue; routing decision is.
- ✓
Add specific routes for S3 public IP prefixes pointing to the internet gateway.
Why this is correct
More specific routes override the general route to VGW, directing S3 traffic to IGW.
- ✗
Add a static route for 0.0.0.0/0 pointing to the internet gateway.
Why it's wrong here
This sends all internet traffic via IGW, but on-premises traffic would also go to IGW, not Direct Connect.
- ✗
Add a static route in the VPC route table for 0.0.0.0/0 pointing to the VGW.
Why it's wrong here
This sends all traffic including S3 through Direct Connect.
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Same concept, more angles
1 more way this is tested on ANS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a Direct Connect connection with a private VIF to a VPC. The on-premises network is advertising a default route (0.0.0.0/0) over BGP. The VPC has an internet gateway attached. When an EC2 instance in the VPC sends traffic to an internet destination, which path does it take by default?
hard- A.Traffic goes to the on-premises network only if there is a static route.
- B.Traffic is dropped because there is no route.
- C.Traffic goes to the internet via the internet gateway.
- ✓ D.Traffic goes to the on-premises network via Direct Connect.
Why D: When an on-premises network advertises a default route (0.0.0.0/0) over BGP via a Direct Connect private VIF, that route is propagated into the VPC route tables as a static route. By default, the most specific route (longest prefix match) is preferred, but since both the internet gateway and the BGP-advertised route are for 0.0.0.0/0, the BGP route takes precedence because it is learned via a more specific path (Direct Connect) and is considered a static route in the VPC route table, overriding the internet gateway's implicit route.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.