ANS-C01 Network Management and Operations Practice Question
Network Topology
An engineer is troubleshooting connectivity from on-premises to a VPC via Direct Connect private VIF. The BGP session is up, traffic is flowing, but the on-premises network cannot reach some subnets in the VPC. The VPC CIDR is 10.0.0.0/16. What is the most likely cause based on the exhibit?
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 security groups or network ACLs in the VPC are blocking traffic to those subnets.
The BGP session being up and traffic flowing indicates that routing is properly configured between on-premises and the VPC. The inability to reach only some subnets suggests the issue is at the network security layer within the VPC. Security groups and network ACLs can block traffic to specific subnets while routing remains intact. Therefore, the most likely cause based on the exhibit is that security groups or NACLs are filtering traffic to those subnets.
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 BGP session is up, but the on-premises router is not receiving the VPC CIDR route due to missing route propagation on the virtual private gateway.
Why it's wrong here
Route propagation is enabled by default on the VGW, so this is unlikely.
- ✗
The customer router configuration snippet is missing the BGP configuration for those subnets.
Why it's wrong here
The customer router config is not shown in detail.
- ✓
The security groups or network ACLs in the VPC are blocking traffic to those subnets.
Why this is correct
Since the VPC CIDR is advertised, reachability issues within the VPC are more likely due to security group or NACL rules.
- ✗
The route filter prefixes only allow the VPC CIDR 10.0.0.0/16, but the VPC has additional CIDRs that are not being advertised.
Why it's wrong here
The question states VPC CIDR is /16, but it could have multiple CIDRs; however, the exhibit shows only one prefix.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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