Creating custom bridge networks in Docker - Practice Exercises

Challenge - 5 Problems

💻 Command Output

intermediate

Output of creating a custom bridge network

What is the output when you run the command to create a custom bridge network named my_bridge?

Docker

docker network create --driver bridge my_bridge

A a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9t0u1v2w3x4y5z6

B Error: network driver not found

C Network my_bridge already exists

D 1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef

💡 Hint

The command returns a network ID which is a long hexadecimal string.

When you create a custom bridge network, Docker returns the network ID, which is a 64-character hexadecimal string. The output confirms successful creation.

🧠 Conceptual

intermediate

Purpose of custom bridge networks

Why would you create a custom bridge network instead of using the default bridge network in Docker?

A To isolate containers and control communication between them

B To increase container CPU usage automatically

C To disable container networking completely

D To allow containers to use host network interfaces directly

💡 Hint

Think about network isolation and container communication control.

Custom bridge networks allow you to isolate containers and control how they communicate, unlike the default bridge network which is shared by all containers.

❓ Configuration

advanced

Correct Docker network create command with subnet

Which command correctly creates a custom bridge network named custom_net with subnet 192.168.100.0/24?

A docker network create --driver bridge --subnet=192.168.100.0/24 custom_net

B docker network create --subnet 192.168.100.0/24 --driver=bridge custom_net

C docker network create custom_net --driver bridge --subnet 192.168.100.0/24

D docker network create --driver=bridge custom_net --subnet=192.168.100.0/24

💡 Hint

The subnet option uses an equals sign and comes after the driver option.

The correct syntax requires the --subnet option with an equals sign and the network name last. Option A follows the correct order and syntax.

❓ Troubleshoot

advanced

Troubleshooting network creation failure

You run docker network create --driver bridge --subnet=192.168.1.0/24 mynet but get the error: Error response from daemon: Pool overlaps with other one on this address space. What is the most likely cause?

A The network name mynet is invalid

B The subnet 192.168.1.0/24 is already used by another Docker network

C The bridge driver is not installed

D The Docker daemon is not running

💡 Hint

The error mentions overlapping address space.

Docker prevents creating networks with overlapping subnets to avoid IP conflicts. The error means the subnet is already in use by another network.

🔀 Workflow

expert

Order of commands to create and use a custom bridge network

Put these steps in the correct order to create a custom bridge network and run a container attached to it:

A 2,4,3,1

B 3,2,4,1

C 2,3,4,1

D 1,2,3,4

💡 Hint

You must create the network before running containers on it.

First create the network (2), then list networks to confirm (3), inspect details (4), and finally run the container attached to it (1).

Practice

1. What is the main purpose of creating a custom bridge network in Docker?

easy

A. To increase the CPU usage of containers

B. To allow containers to communicate privately and securely

C. To automatically update container images

D. To create a backup of container data

Solution

1. Step 1: Understand Docker networking basics

   Docker uses networks to connect containers. The default bridge network is shared and less secure.

2. Step 2: Purpose of custom bridge networks

   Custom bridge networks isolate containers, allowing private and secure communication between them.

3. Final Answer:

   To allow containers to communicate privately and securely -> Option B

4. Quick Check:

   Custom bridge network = private container communication [OK]

Hint: Custom bridge = private container communication [OK]

Common Mistakes:

• Thinking custom bridge increases CPU usage
• Confusing network creation with image updates
• Assuming it creates data backups

2. Which of the following is the correct command to create a custom bridge network named my_bridge?

easy

A. docker network create --driver bridge my_bridge

B. docker create network bridge my_bridge

C. docker network new --type bridge my_bridge

D. docker bridge create network my_bridge

Solution

1. Step 1: Recall Docker network creation syntax

   The correct syntax is docker network create --driver bridge NETWORK_NAME.

2. Step 2: Match the command with the syntax

   docker network create --driver bridge my_bridge matches the correct syntax exactly for creating a bridge network named my_bridge.

3. Final Answer:

   docker network create --driver bridge my_bridge -> Option A

4. Quick Check:

   Correct syntax = docker network create --driver bridge [OK]

Hint: Use 'docker network create --driver bridge NAME' [OK]

Common Mistakes:

• Using wrong command order
• Missing --driver flag
• Using 'new' or 'create' incorrectly

3. Given the command docker network create --driver bridge isolated_net, what will be the output of docker network ls related to this network?

medium

A. No change; the network list remains the same

B. An error message saying 'driver not found' will appear

C. The default bridge network will be removed

D. A new network named 'isolated_net' with driver 'bridge' will appear in the list

Solution

1. Step 1: Understand the effect of the create command

   The command creates a new bridge network named 'isolated_net'.

2. Step 2: Check the network list after creation

   Running docker network ls shows all networks including the newly created 'isolated_net' with driver 'bridge'.

3. Final Answer:

   A new network named 'isolated_net' with driver 'bridge' will appear in the list -> Option D

4. Quick Check:

   New bridge network appears in list [OK]

Hint: New bridge network shows in 'docker network ls' [OK]

Common Mistakes:

• Expecting an error for valid driver
• Thinking default bridge is removed
• Assuming no change in network list

4. You ran docker network create --driver bridge without specifying a network name. What is the likely result?

medium

A. Docker creates a network named 'bridge' by default

B. Docker creates a network with a random generated name

C. Docker throws an error about missing network name

D. Docker creates the default bridge network again

Solution

1. Step 1: Check required arguments for network creation

   The docker network create command requires a network name after options.

2. Step 2: Result of missing network name

   Omitting the network name causes Docker to throw an error indicating the missing argument.

3. Final Answer:

   Docker throws an error about missing network name -> Option C

4. Quick Check:

   Missing name causes error [OK]

Hint: Always specify network name after options [OK]

Common Mistakes:

• Assuming Docker auto-generates network name
• Thinking 'bridge' is default name created
• Confusing with default bridge network

5. You want two containers to communicate only with each other and not with other containers on the host. Which steps correctly create and use a custom bridge network named private_net?

hard

A. Create network with docker network create --driver bridge private_net and run containers with --network private_net

B. Run containers with --link option without creating a network

C. Use default bridge network and assign static IPs manually

D. Create network with docker network create private_net without specifying driver

Solution

1. Step 1: Create a custom bridge network

   Use docker network create --driver bridge private_net to create an isolated network.

2. Step 2: Run containers attached to this network

   Start containers with --network private_net so they communicate only within this network.

3. Final Answer:

   Create network with 'docker network create --driver bridge private_net' and run containers with '--network private_net' -> Option A

4. Quick Check:

   Custom bridge + --network = isolated container communication [OK]

Hint: Create bridge network then run containers with --network [OK]

Common Mistakes:

• Using --link which is deprecated
• Relying on default bridge for isolation
• Omitting --driver option causing default driver