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CV0-004 Practice Question: A cloud administrator is troubleshooting a…

A cloud administrator is troubleshooting a connectivity issue between two virtual machines in the same VPC but different subnets. Both VMs have security groups that allow all traffic from the VPC CIDR. What should the administrator check first?

⚠ Common exam trap

It's easy for candidates to assume security groups alone control all traffic, forgetting that NACLs are stateless and must be configured for both inbound and outbound directions on each subnet involved.

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 network ACLs for both subnets.

Network ACLs are stateless and evaluate traffic entering and leaving a subnet. Even if security groups allow all traffic from the VPC CIDR, a default or custom NACL rule might implicitly deny traffic between subnets. Since the VMs are in different subnets, the NACL for each subnet must be checked first to ensure inbound and outbound rules permit the traffic.

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 VPC flow logs.

    Why it's wrong here

    Flow logs are useful for diagnosis but not the first thing to check; checking NACLs is more direct.

  • The network ACLs for both subnets.

    Why this is correct

    NACLs are stateless and may be blocking traffic even if security groups allow it.

  • The route tables for both subnets.

    Why it's wrong here

    VPC automatically adds a local route, so route tables are unlikely to be the issue.

  • The DHCP option set.

    Why it's wrong here

    DHCP options are for DNS and domain, not connectivity between subnets.

Visual reference

192.168.1.0 /24 256 addresses (254 usable) 192.168.1.0 /25 Subnet A 128 addr (126 usable) 192.168.1.128 /25 Subnet B 128 addr (126 usable) Borrowing 1 bit from host portion creates 2 subnets (/25)

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This CV0-004 practice question is part of Courseiva's free CompTIA 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 CV0-004 exam.