Network inspection and debugging in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Inspect Docker container network details

You run the command docker network inspect bridge. What key information does this command provide about the Docker bridge network?

A It displays the CPU and memory usage of all running containers.

B It shows the containers connected to the bridge network, their IP addresses, and network settings.

C It lists all Docker images available on the host machine.

D It removes the bridge network and disconnects all containers.

💡 Hint

Think about what 'inspect' means in Docker networking context.

The docker network inspect command shows detailed information about a specific network, including connected containers and their IP addresses.

💻 Command Output

intermediate

Diagnose container connectivity with ping

You have two containers on the same user-defined Docker network. You run docker exec container1 ping -c 3 container2. What output do you expect if the network is correctly configured?

A 3 packets transmitted, 3 received, 0% packet loss, time=XYZ ms

B ping: unknown host container2

C Permission denied

D connect: Network is unreachable

💡 Hint

Successful ping means packets reach the target container.

If containers are on the same network and reachable, ping will show all packets received with no loss.

❓ Troubleshoot

advanced

Troubleshoot Docker container cannot reach external internet

A container cannot access the internet, but other containers on the same host can. Which Docker network setting is most likely causing this?

A The container is connected to a user-defined bridge network without proper DNS or gateway settings.

B The container is running with the <code>--network host</code> option.

C The container has <code>--restart always</code> set.

D The container is using a volume mount for /etc/hosts.

💡 Hint

Check network isolation and DNS configuration.

User-defined bridge networks require proper DNS and gateway settings for internet access. Missing these can block external connectivity.

✅ Best Practice

advanced

Best practice for inspecting live network traffic of a container

You want to capture and analyze live network traffic inside a running Docker container. Which approach is best?

A Modify the container's Dockerfile to add network capture tools and rebuild.

B Restart the container with <code>--net=host</code> to capture traffic on the host.

C Use <code>docker logs</code> to view network packets.

D Use <code>docker exec</code> to run <code>tcpdump</code> inside the container if installed.

💡 Hint

Think about capturing traffic without restarting or rebuilding.

Running tcpdump inside the container via docker exec allows live capture without downtime.

🔀 Workflow

expert

Order the steps to debug a Docker container network issue

Arrange these steps in the correct order to debug why a Docker container cannot connect to another container on the same network.

A 1,3,2,4

B 2,1,3,4

C 1,2,3,4

D 3,1,2,4

💡 Hint

Start with network configuration, then test connectivity, then check host settings, then logs.

First confirm network setup, then test connectivity, then check host firewall, finally check logs for app errors.