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CV0-002 · 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. When two virtual machines (VMs) are located within the same subnet but cannot communicate, a common cause is an incorrect firewall configuration. Firewalls, whether host-based or network-based, can block traffic between endpoints despite proper network configuration.

Troubleshooting

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

(40 responses)
  • A
    8% (3)
  • B
    5% (2)
  • C
    3% (1)
  • D
    85% (34)

Why each option

When two virtual machines (VMs) are located within the same subnet but cannot communicate, a common cause is an incorrect firewall configuration. Firewalls, whether host-based or network-based, can block traffic between endpoints despite proper network configuration.

APrivate IP addresses are not routable

Private IP addresses are perfectly routable and communicable within a private network and its subnets; the issue of non-routability applies mainly to routing over the public internet.

BIncorrect VLAN tagging

While incorrect VLAN tagging could separate VMs at Layer 2, preventing communication, an incorrect firewall configuration is a more direct and common reason for communication failure between VMs assumed to be correctly connected at Layer 2 and Layer 3.

CIncorrect subnetting

The question explicitly states the VMs are in the 'same subnet 10.120.10.x/24', indicating the subnetting itself is understood to be correct, thus ruling out incorrect subnetting as the problem.

DIncorrect firewall configurationCorrect

Even if two VMs are in the same subnet and have correct IP configurations, their host-based firewalls (e.g., Windows Firewall, iptables) or network security groups/virtual firewalls can be configured to block traffic between them, preventing communication.

Concept tested: Firewall rules and network connectivity

Topics

#network troubleshooting#VM networking#firewall rules#subnet communication

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