The most probable cause is an invalid or incorrect default gateway address on that computer.

Quick Scoop: What’s Going On?

When a computer can talk to devices on the same LAN but not outside it, it usually means local communication is fine, but traffic that should go to other networks never reaches a router.

The device that knows how to reach other networks is the default gateway (typically a router interface).

So if the default gateway is missing, wrong, or on the wrong subnet, the PC has no idea where to send packets destined for other networks.

In exam-style networking questions with options like “invalid IP,” “incorrect subnet mask,” and “invalid default gateway,” the expected answer for this exact symptom is: invalid default gateway address.

Why not the other options?

  • Invalid IP address
    If the IP were invalid or on the wrong network, the computer usually would not be able to talk even to other local devices.
  • Incorrect subnet mask
    A bad subnet mask often breaks both local and remote communication or causes very inconsistent behavior, not “local works, remote doesn’t” in such a clean way.
  • Cable not connected properly
    A bad cable would prevent almost all connectivity, including to same-network devices, which is not the case here.

Mini checklist (real-world angle)

In a real troubleshooting scenario, you would typically verify on the affected PC:

  1. IP address:
    • Is it in the same subnet as the other local devices?
  2. Subnet mask:
    • Does it match the rest of the network?
  3. Default gateway (most important here):
    • Is it set?
    • Is it the router’s correct IP on that subnet?
    • Can you ping it?

If 1 and 2 are fine and only off-network access fails, an incorrect default gateway setting is the classic root cause, and that matches how this question is typically answered in networking quizzes and exams.

TL;DR:
For the question:

“A computer can access devices on the same network but cannot access devices on other networks. What is the probable cause of this problem?”

The expected and technically correct answer is: The computer has an invalid default gateway address.

Information gathered from public forums or data available on the internet and portrayed here.