CV0-003 · Question #152
Two VMs are in the same subnet 10.120.10.x/24, but the VMs cannot communicate with each other. Which of the following could be causing this problem?
The correct answer is D. Incorrect firewall configuration. Two VMs sharing the same /24 subnet can still fail to communicate if a firewall or security policy is blocking traffic between them at the host or network level.
Question
Two VMs are in the same subnet 10.120.10.x/24, but the VMs cannot communicate with each other. Which of the following could be causing this problem?
Options
- APrivate IP addresses are not routable
- BIncorrect VLAN tagging
- CIncorrect subnetting
- DIncorrect firewall configuration
How the community answered
(42 responses)- A2% (1)
- B12% (5)
- C5% (2)
- D81% (34)
Why each option
Two VMs sharing the same /24 subnet can still fail to communicate if a firewall or security policy is blocking traffic between them at the host or network level.
Private RFC 1918 IP addresses are fully routable within a local network and are the standard addressing scheme used for VMs on the same subnet - they do not prevent communication.
VLAN tagging issues would prevent layer 2 reachability entirely, but the question already confirms both VMs share the same subnet, making this an unlikely cause for intra-segment communication failure.
Both VMs are explicitly stated to reside in the same 10.120.10.x/24 subnet, ruling out incorrect subnetting as the cause.
When VMs are confirmed to be on the same subnet, IP routing and addressing are not barriers - traffic stays local at layer 2/3. Firewall rules, host-based firewalls, or cloud security groups can still block intra-subnet traffic regardless of subnet membership, making misconfigured firewall policy the most likely culprit.
Concept tested: Intra-subnet VM traffic blocked by firewall policy
Source: https://learn.microsoft.com/en-us/azure/virtual-network/network-security-groups-overview
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