Bridge network default behavior in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to list all Docker networks.

Docker

docker network [1]

Drag options to blanks, or click blank then click option'

Als

Binspect

Crm

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'create' instead of 'ls' will try to make a new network.

'rm' deletes a network, not lists it.

The docker network ls command lists all Docker networks on your system.

2fill in blank

medium

Complete the command to create a new bridge network named 'mybridge'.

Docker

docker network create --driver [1] mybridge

Drag options to blanks, or click blank then click option'

Ahost

Bnone

Cbridge

Doverlay

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'host' connects containers directly to the host network.

'overlay' is for multi-host networking.

The bridge driver creates a bridge network, which is the default network type in Docker.

3fill in blank

hard

Fix the error in the command to inspect the default bridge network.

Docker

docker network [1] bridge

Drag options to blanks, or click blank then click option'

Ainspect

Brm

Cls

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ls' lists networks but does not show details.

'rm' deletes the network, which is not intended here.

The docker network inspect command shows detailed information about a network, such as the default bridge.

4fill in blank

hard

Fill both blanks to create a container named 'web' attached to the default bridge network.

Docker

docker run --name [1] --network [2] -d nginx

Drag options to blanks, or click blank then click option'

Aweb

Bhost

Cbridge

Dmybridge

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'host' network changes container networking behavior.

Using 'mybridge' is a custom network, not default.

The container is named 'web' and attached to the 'bridge' network, which is the default Docker bridge network.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps container names to their IP addresses from a list 'containers'.

Docker

container_ips = {{ [1]: [2] for [3] in containers }}

Drag options to blanks, or click blank then click option'

Acontainer.name

Bcontainer.attrs['NetworkSettings']['IPAddress']

Ccontainer

Dcontainer.id

Attempts:

3 left

💡 Hint

Common Mistakes

Using container.id as key instead of name.

Using wrong attribute for IP address.

This comprehension creates a dictionary where keys are container names and values are their IP addresses, iterating over each container in 'containers'.

Practice

1. What is the default behavior of Docker's bridge network regarding container communication?

easy

A. Containers can communicate by container name without extra setup.

B. Containers cannot communicate with each other at all.

C. Containers can communicate with each other by IP address only.

D. Containers share the host network directly.

Solution

1. Step 1: Understand bridge network basics

   The default bridge network connects containers on the same Docker host and allows communication by IP address.

2. Step 2: Analyze name resolution behavior

   By default, containers on the bridge network cannot resolve each other's names without a custom network.

3. Final Answer:

   Containers can communicate with each other by IP address only. -> Option C

4. Quick Check:

   Bridge network communication = IP only [OK]

Hint: Default bridge allows IP communication, not name resolution [OK]

Common Mistakes:

• Assuming container names resolve by default
• Thinking containers share host network directly
• Believing containers cannot communicate at all

2. Which Docker command shows the default bridge network details?

easy

A. docker info bridge

B. docker network ls

C. docker container ls

D. docker network inspect bridge

Solution

1. Step 1: Identify command to inspect networks

   To see details of a specific network, use docker network inspect <network-name>.

2. Step 2: Apply to default bridge network

   The default bridge network is named "bridge", so the command is docker network inspect bridge.

3. Final Answer:

   docker network inspect bridge -> Option D

4. Quick Check:

   Inspect bridge network = docker network inspect bridge [OK]

Hint: Inspect networks with 'docker network inspect <name>' [OK]

Common Mistakes:

• Using 'docker container ls' to see networks
• Trying 'docker info bridge' which is invalid
• Confusing 'docker network ls' with inspect

3. Given two containers on the default bridge network, what happens if you try to ping one container by its name from the other?

medium

A. Ping fails because default bridge does not support container name resolution.

B. Ping fails unless containers are on a custom network.

C. Ping succeeds only if containers share the same image.

D. Ping succeeds because default bridge supports name resolution.

Solution

1. Step 1: Recall default bridge network name resolution

   The default bridge network does not provide automatic DNS resolution for container names.

2. Step 2: Understand ping behavior by name

   Trying to ping by container name will fail because the name cannot be resolved to an IP address.

3. Final Answer:

   Ping fails because default bridge does not support container name resolution. -> Option A

4. Quick Check:

   Default bridge name resolution = no [OK]

Hint: Default bridge lacks DNS for container names [OK]

Common Mistakes:

• Assuming ping by name works by default
• Confusing image sharing with network name resolution
• Thinking custom networks are not needed

4. You created two containers on the default bridge network and tried to connect them by name, but it failed. What is the likely cause?

medium

A. The containers are not running.

B. You forgot to create a user-defined bridge network.

C. The Docker daemon is not started.

D. You used the wrong container names.

Solution

1. Step 1: Understand default bridge limitations

   Default bridge network does not support container name resolution for communication.

2. Step 2: Identify solution for name-based communication

   Creating a user-defined bridge network enables automatic DNS resolution of container names.

3. Final Answer:

   You forgot to create a user-defined bridge network. -> Option B

4. Quick Check:

   Name resolution needs user-defined bridge [OK]

Hint: Use user-defined bridge for name resolution [OK]

Common Mistakes:

• Blaming container state without checking network
• Assuming Docker daemon is stopped without evidence
• Ignoring network type for name resolution

5. You want two containers to communicate by name and also access the internet. Which approach using Docker's networking should you take?

hard

A. Connect both containers to a user-defined bridge network which supports name resolution and NAT for internet access.

B. Use the default bridge network and manually edit /etc/hosts in each container.

C. Connect containers to the host network to share internet and name resolution.

D. Create a macvlan network to enable name resolution and internet access.

Solution

1. Step 1: Identify network supporting name resolution and NAT

   User-defined bridge networks provide automatic DNS for container names and NAT for internet access.

2. Step 2: Evaluate other options

   Default bridge lacks name resolution; host network shares host IP but no DNS; macvlan isolates containers and does not provide NAT by default.

3. Final Answer:

   Connect both containers to a user-defined bridge network which supports name resolution and NAT for internet access. -> Option A

4. Quick Check:

   User-defined bridge = name resolution + NAT [OK]

Hint: User-defined bridge = name resolution + internet [OK]

Common Mistakes:

• Editing /etc/hosts manually is error-prone
• Assuming host network provides container DNS
• Using macvlan without NAT causes no internet