Inspecting container network settings in Docker - Step-by-Step Execution

Process Flow - Inspecting container network settings

Start: Docker container running

↓

Run 'docker network ls'

↓

List all networks

↓

Run 'docker network inspect <network>'

↓

View detailed network info

↓

Identify container's IP, gateway, subnet

↓

Use info for troubleshooting or config

This flow shows how to list Docker networks and inspect details of a specific network to see container IPs and settings.

Execution Sample

Docker

docker network ls
docker network inspect bridge

List all Docker networks, then inspect the default 'bridge' network to see container network details.

Process Table

Step	Command Run	Action	Output Summary
1	docker network ls	List all Docker networks	Shows networks: bridge, host, none
2	docker network inspect bridge	Inspect 'bridge' network details	JSON with containers, IP ranges, gateway
3	Locate container info in JSON	Find container's IP and settings	Container ID, IPv4Address, MacAddress shown
4	Use info for troubleshooting	Check connectivity or config	Confirm container IP and subnet
5	End	Finished inspection	Ready for next steps

💡 Inspection complete after viewing container network details in the bridge network

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
networks_list	empty	[bridge, host, none]	[bridge, host, none]	[bridge, host, none]
network_details	none	JSON data of bridge network	Parsed container IP and MAC	Parsed container IP and MAC
container_ip	unknown	unknown	172.17.0.2/16	172.17.0.2/16

Key Moments - 3 Insights

Why do we run 'docker network ls' before inspecting a network?

Because 'docker network ls' shows all available networks so you know which network name to inspect, as seen in step 1 of the execution table.

How do we find the container's IP address in the inspect output?

The IP is inside the JSON under 'Containers' with the key 'IPv4Address', shown in step 3 of the execution table.

What if the container is not listed in the network inspect output?

It means the container is not connected to that network; you should check other networks or container settings.

Visual Quiz - 3 Questions

Look at the execution table, what command lists all Docker networks?

A docker network inspect bridge

B docker ps

C docker network ls

D docker container ls

💡 Hint

See Step 1 in the execution table where 'docker network ls' lists networks.

At which step do we find the container's IP address?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Step 3 shows locating container info including IP in the JSON output.

If the container IP was not found in 'bridge' network inspect, what should you do?

A Inspect other networks

B Remove the container

C Restart Docker daemon

D Run 'docker ps' again

💡 Hint

Key moment 3 explains checking other networks if container is missing.

Concept Snapshot

docker network ls  # Lists all Docker networks

docker network inspect <network>  # Shows detailed info of a network

Look inside 'Containers' section for container IPs and MACs

Use this info to troubleshoot container connectivity

If container missing, check other networks

Full Transcript

To inspect container network settings in Docker, first list all networks using 'docker network ls'. This shows available networks like bridge, host, and none. Next, run 'docker network inspect <network>' to see detailed info about that network. The output is JSON containing IP ranges, gateways, and connected containers. Find your container's ID under 'Containers' and note its IPv4Address and MacAddress. This info helps verify container IP and troubleshoot network issues. If the container is not listed, it may be connected to a different network. Repeat inspection for other networks as needed.

Practice

1. Which Docker command shows detailed information about a specific network, including connected containers?

easy

A. docker ps

B. docker container inspect <container_id>

C. docker network inspect <network_name>

D. docker network ls

Solution

1. Step 1: Understand the purpose of docker network inspect

   This command provides detailed info about a Docker network, including which containers are connected.

2. Step 2: Compare with other commands

   docker container inspect shows container details, docker ps lists running containers, and docker network ls lists networks without details.

3. Final Answer:

   docker network inspect <network_name> -> Option C

4. Quick Check:

   Network details = docker network inspect [OK]

Hint: Use docker network inspect for network details [OK]

Common Mistakes:

• Confusing container inspect with network inspect
• Using docker ps to get network info
• Using docker network ls for detailed info

2. Which of the following commands correctly shows the IP address of a running container named webapp using docker container inspect with formatting?

easy

A. docker container inspect --format '{{.NetworkSettings.IPAddress}}' webapp

B. docker container inspect --format '{{.Network.IP}}' webapp

C. docker inspect --format '{{.NetworkSettings.IP}}' webapp

D. docker container inspect --format '{{.IPAddress}}' webapp

Solution

1. Step 1: Identify correct JSON path for IP address

   The IP address is under .NetworkSettings.IPAddress in container inspect output.

2. Step 2: Check command syntax

   docker container inspect --format '{{.NetworkSettings.IPAddress}}' webapp uses correct command and format string. Others use incorrect paths or omit 'container'.

3. Final Answer:

   docker container inspect --format '{{.NetworkSettings.IPAddress}}' webapp -> Option A

4. Quick Check:

   IP address path = .NetworkSettings.IPAddress [OK]

Hint: Use .NetworkSettings.IPAddress to get container IP [OK]

Common Mistakes:

• Using wrong JSON path like .Network.IP
• Omitting 'container' in the command
• Using '{{.IPAddress}}' which is invalid

3. Given a container named db connected to a network backend_net, what will the command docker network inspect backend_net show about the container?

medium

A. It lists the container ID and its IPv4 address inside the network.

B. It shows only the container name without IP details.

C. It shows the container's CPU and memory usage.

D. It shows the container's logs.

Solution

1. Step 1: Understand output of docker network inspect

   This command shows network details including connected containers with their IDs and IP addresses.

2. Step 2: Eliminate incorrect options

   It does not show CPU/memory usage or logs, and it includes IP info, not just names.

3. Final Answer:

   It lists the container ID and its IPv4 address inside the network. -> Option A

4. Quick Check:

   Network inspect shows container IDs and IPs [OK]

Hint: Network inspect shows container IDs and IPs connected [OK]

Common Mistakes:

• Expecting resource usage info from network inspect
• Thinking it shows logs
• Assuming only container names appear

4. You run docker container inspect --format '{{.NetworkSettings.IPAddress}}' myapp but get an empty output. What is the most likely reason?

medium

A. The container myapp is not connected to the default bridge network.

B. Docker daemon is not running.

C. The command syntax is incorrect.

D. The container myapp is stopped.

Solution

1. Step 1: Understand when IPAddress is empty

   If a container is stopped, it has no active network interface, so IPAddress is empty.

2. Step 2: Check other options

   Not connected to default network still shows IP if connected elsewhere; syntax is correct; daemon not running causes errors, not empty output.

3. Final Answer:

   The container myapp is stopped. -> Option D

4. Quick Check:

   Stopped container IP is empty [OK]

Hint: Empty IP means container likely stopped [OK]

Common Mistakes:

• Assuming wrong syntax causes empty output
• Thinking network choice causes empty IP
• Ignoring container running state

5. You want to list all containers connected to a custom network mynet and show their names and IP addresses in a simple table. Which approach is best?

hard

A. Run docker ps and guess which containers belong to mynet.

B. Use docker network inspect mynet and parse the JSON to extract container names and IPs.

C. Use docker container inspect --format '{{.Name}} {{.NetworkSettings.IPAddress}}' on all containers and filter manually.

D. Restart Docker daemon to refresh network info.

Solution

1. Step 1: Identify command that shows network container info

   docker network inspect mynet lists all containers connected with their IPs.

2. Step 2: Understand why other options are less effective

   docker ps doesn't show network info; inspecting all containers is manual and error-prone; restarting daemon is unrelated.

3. Final Answer:

   Use docker network inspect mynet and parse the JSON to extract container names and IPs. -> Option B

4. Quick Check:

   Network inspect shows connected containers best [OK]

Hint: Use docker network inspect to get connected containers easily [OK]

Common Mistakes:

• Using docker ps to find network info
• Inspecting containers individually without filtering
• Restarting daemon unnecessarily