Question 606 of 989
easyMultiple ChoiceObjective-mapped
200-901 Practice Question: Refer to the exhibit
Network Topology
Refer to the exhibit. A developer builds this Docker image and runs it. The container starts but cannot be accessed on port 5000 from the host. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the misconception that EXPOSE publishes the port, when in fact it only documents the port and requires `-p` or `-P` for actual host access.
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 EXPOSE instruction does not publish the port; the container was run without -p.
The EXPOSE instruction in a Dockerfile is documentation only; it does not actually publish the container's port to the host. For the container to be accessible on port 5000 from the host, the container must be run with the `-p` (or `--publish`) flag (e.g., `docker run -p 5000:5000 ...`). Without this, the container's port 5000 is only reachable from within the Docker network, not from the host.
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 requirements.txt is missing Flask.
Why it's wrong here
If Flask were missing, the application would fail to start, not just be unreachable.
- ✗
The Python application is not listening on 0.0.0.0.
Why it's wrong here
While possible, this is less likely than the port not being published; the default Flask server listens on 0.0.0.0.
- ✗
The container is using a different port inside.
Why it's wrong here
The Dockerfile exposes port 5000, and the CMD runs app.py, typically on port 5000.
- ✓
The EXPOSE instruction does not publish the port; the container was run without -p.
Why this is correct
EXPOSE is documentation; without -p, no port is published to the host.
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Last reviewed: Jun 24, 2026
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