We can recreate this exact switch-trunking lab in Cisco Packet Tracer. The key concept is:

Access ports connect end devices to one VLAN. Trunk port carries multiple VLANs between switches.

One small correction in the image: the SW2 configuration appears to show vlan 18 and vlan 38, but based on the topology it should be VLAN 10, 20, and 30.

why a company needs trunking.

Let's forget Packet Tracer for a moment and look at an actual corporate office.

Imagine your Cubic office

Suppose an office has 200 employees and one switch has 48 ports.
The company doesn't want every device to be in the same network.

They may create:

• VLAN 10 → Employees
• VLAN 20 → IT/Servers
• VLAN 30 → Guest Wi-Fi
• VLAN 40 → CCTV
• VLAN 50 → Voice/IP Phones

So physically you might have:

Now comes the important question:

Why do we need a TRUNK?

Imagine SW1 and SW2 are on different floors.

But users on both floors need access to the same VLANs.

For example:

 
SW1                          SW2

Employee VLAN 10 ─────────── VLAN 10
IT VLAN 20      ─────────── VLAN 20
Guest VLAN 30   ─────────── VLAN 30
Voice VLAN 40   ─────────── VLAN 40

Do we need four physical cables?

SW1 ================= SW2   VLAN 10

SW1 ================= SW2   VLAN 20

SW1 ================= SW2   VLAN 30

SW1 ================= SW2   VLAN 40

That would be inefficient.

Instead, we use one trunk link:

That's the main reason for trunking.

1. Create the topology

In Packet Tracer, add:

2 × 2960 switches
4 × PCs


Arrange them:  

 More precisely:

Connections

     
 Device	   Port	               Device	     Port	Type
  PC1	   FastEthernet0	SW1	     Fa0/1	Copper Straight-Through
  PC2	   FastEthernet0	SW1	     Fa0/2	Copper Straight-Through
  SW1	   Fa0/24	        SW2          Fa0/24	Copper Cross-Over*
  PC3	   FastEthernet0	SW2	     Fa0/1	Copper Straight-Through
  PC4	   FastEthernet0	SW2	     Fa0/2	Copper Straight-Through


                         www.kumaratuljaiswal.in

2. Create VLANs on SW1

Click SW1 → CLI. 

enable
configure terminal

vlan 10
name VLAN10
exit

vlan 20
name VLAN20
exit

vlan 30
name VLAN30
exit

So SW1 now has:

• VLAN 10
• VLAN 20
• VLAN 30 

3. Configure PC1 port as VLAN 10

PC1 is connected to SW1 Fa0/1.


This means:

interface fa0/1
switchport mode access
switchport access vlan 10
exit

  

4. Configure PC2 port as VLAN 20

interface fa0/2
switchport mode access
switchport access vlan 20
exit

5. Configure SW1-to-SW2 as a trunk

This is the most important part.

On SW1: 

interface fa0/24
switchport mode trunk
switchport trunk allowed vlan 10,20
exit

Notice:

allowed vlan 10,20

We are not allowing VLAN 30.

Therefore:

• VLAN 10 → Allowed
• VLAN 20 → Allowed
• VLAN 30 → Blocked 

6. Configure SW2

Go to SW2 → CLI.

Create the same VLANs:
 

enable
configure terminal

vlan 10
name VLAN10
exit

vlan 20
name VLAN20
exit

vlan 30
name VLAN30
exit

7. Configure PC3 as VLAN 10

PC3 is connected to SW2 Fa0/1:
 

interface fa0/1
switchport mode access
switchport access vlan 10
exit

8. Configure PC4 as VLAN 20

interface fa0/2
switchport mode access
switchport access vlan 20
exit

9. Configure SW2 trunk 

interface fa0/24
switchport mode trunk
switchport trunk allowed vlan 10,20
exit

Now both sides of the trunk agree: 

SW1 Fa0/24
      ||
      ||  802.1Q TRUNK
      ||
SW2 Fa0/24


Allowed VLANs:
10
20

VLAN 30:
NOT ALLOWED 

10. Configure PC IP addresses

Go to each PC:

PC → Desktop → IP Configuration


PC1

• IP Address: 192.168.10.10
• Subnet Mask: 255.255.255.0

PC2

• IP Address: 192.168.20.10
• Subnet Mask: 255.255.255.0

PC3

• IP Address: 192.168.10.20
• Subnet Mask: 255.255.255.0

PC4

• IP Address: 192.168.20.20
• Subnet Mask: 255.255.255.0

You don't need a default gateway for this particular lab because we're only testing Layer-2 communication within the same VLAN.

11. Test the important part

From PC1:

• ping 192.168.10.20

Expected:

• Reply from 192.168.10.20

Why? 

PC1
VLAN 10
   ↓
SW1
   ↓
TRUNK
   ↓
SW2
   ↓
VLAN 10
   ↓
PC3

So PC1 → PC3 should work.

Now from PC2:

ping 192.168.20.20

Expected:

Reply from 192.168.20.20

Because both are VLAN 20. 

12. Test between different VLANs


From PC1:

ping 192.168.20.20

This should fail.

Why?

PC1 → VLAN 10
             X
         VLAN 20

A Layer-2 switch does not route between VLAN 10 and VLAN 20. You would need a router or Layer-3 switch for inter-VLAN routing.

13. Verify the VLANs

On SW1:

• show vlan brief

You should see something similar to:

VLAN Name       Status    Ports

10   VLAN10     active    Fa0/1
20   VLAN20     active    Fa0/2
30   VLAN30     active

On SW2:

• show vlan brief

10   VLAN10     active    Fa0/1
20   VLAN20     active    Fa0/2
30   VLAN30     active  
  

  
| Test          | Expected                              |
| ------------- | ------------------------------------- |
| PC1 → PC3     | ✅ Works — same VLAN 10                |
| PC2 → PC4     | ✅ Works — same VLAN 20                |
| PC1 → PC2/PC4 | ❌ Fails — different VLANs, no routing |

  

Multi-Container Applications in Docker: A Beginner's Guide

Modern applications rarely run inside a single container. In real-world production environments, different components of an application are separated into multiple containers. This approach improves scalability, maintainability, security, and performance.

In this guide, you'll learn what multi-container applications are, why they are important, and how Docker Networks and Docker Volumes help containers communicate and store data efficiently.

What Are Multi-Container Applications?

A multi-container application consists of multiple Docker containers working together to provide a complete service.

For example, a typical web application may have:

• React Frontend
• Node.js Backend API
• MongoDB Database

Instead of running everything inside one container, each service runs in its own container. 

React Frontend
      │
      ▼
Node.js Backend
      │
      ▼
MongoDB Database

This architecture follows the principle of separation of concerns, making applications easier to manage and scale.

 

Example Multi-Container Architecture

A typical Docker application may look like this:

Container 1: Frontend
Technology: React
Port: 3000

Container 2: Backend
Technology: Node.js
Port: 5000

Container 3: Database
Technology: MongoDB
Port: 27017

Frontend Container (React)
         │
         ▼
Backend Container (Node.js)
         │
         ▼
Database Container (MongoDB)

 
All containers communicate through a Docker Network.

Why Use Multiple Containers?

Using separate containers provides several advantages:

Better Scalability

You can scale only the service that needs additional resources.


Example:

• 1 MongoDB container
• 3 Backend containers
• 2 Frontend containers

Easier Maintenance

If the backend crashes, you can restart only the backend container without affecting the frontend or database.

Improved Security

Each service runs in an isolated environment.

Independent Updates

Frontend, backend, and database can be updated separately. 

Creating a MongoDB Container

Start a MongoDB container:

docker run -d --name mongodb mongo

Docker downloads the MongoDB image and runs it in the background.

Creating a Custom Docker Network

Starting the Backend Container

Run the backend container on the custom network:

• docker run -d --name backend --network mynetwork node

The backend can now communicate with other containers attached to the same network.


Starting the Frontend Container

Run the frontend container:

• docker run -d --name frontend --network mynetwork react-app

Now all services are connected through the Docker network.

Docker Volumes for Persistent Data
Containers are temporary by nature. If a database container is deleted, its data may be lost.
Docker Volumes solve this problem.

Create a Volume

• docker volume create mydata

List available volumes:

• docker volume ls
• Attach Volume to a Container
• docker run -v mydata:/app/data nginx

 
Benefits of Docker Volumes:

• Persistent storage
• Data survives container deletion
• Easy backup and migration
• Real-World Example: hackingtruth.org

Imagine hosting hackingtruth.org using Docker.

 

Application Stack:

• React Frontend
• Node.js Backend
• MongoDB Database

Production Architecture:

Frontend Container
        │
        ▼
Backend Container
        │
        ▼
MongoDB Container

Supporting Components:

Docker Network → Container communication
Docker Volume → Database storage
Multi-Container Architecture → Service separation


This setup closely resembles how modern applications are deployed in cloud environments.

Essential Commands

Create Volume
docker volume create mydata

List Volumes
docker volume ls

Create Network
docker network create mynetwork

List Networks
docker network ls

Run Container with Volume
docker run -v mydata:/app/data nginx

Run Container on a Network
docker run --network mynetwork nginx

Benefits of Multi-Container Applications

• Better scalability
• Easier troubleshooting
• Improved security
• Independent deployments
• Simplified maintenance
• Production-ready architecture

These advantages make multi-container applications the preferred approach in modern DevOps and cloud-native environments.

Conclusion

Multi-container applications are a fundamental concept in Docker and modern application deployment. By separating frontend, backend, and database services into individual containers, organizations achieve better scalability, reliability, and maintainability.

Combined with Docker Networks and Docker Volumes, multi-container architecture provides the foundation for deploying professional-grade applications in production environments. Learning these concepts is essential for anyone pursuing a career in DevOps, Cloud Engineering, System Administration, or Software Development.

Docker Compose, React & Node.js Deployment, and Container Troubleshooting Guide

As applications grow, managing multiple Docker containers manually becomes difficult. Imagine starting separate containers for React, Node.js, MongoDB, Redis, and Nginx every time you want to run your project.

Docker Compose solves this problem by allowing you to define and manage multi-container applications using a single configuration file.

In this guide, you'll learn Docker Compose, deploying React and Node.js applications, and common container troubleshooting techniques.

What is Docker Compose?

Docker Compose is a tool that allows you to define and run multiple Docker containers using a single YAML configuration file.

Instead of running multiple commands manually:

  
docker run ...
docker run ...
docker run ...

  

You can define everything inside a single file:

docker-compose.yml

and start all services with one command. 

Why Use Docker Compose?

Benefits include:

• Simplified container management
• Easy multi-container deployments
• Better configuration management
• Consistent development environments
• Faster application startup

Docker Compose is commonly used for:

• React Applications
• Node.js APIs
• MongoDB Databases
• Redis Caching
• Nginx Reverse Proxies

Understanding docker-compose.yml

A basic Docker Compose file looks like this:

In this example:

frontend runs the React application
backend runs the Node.js API
database runs MongoDB

All services are automatically connected through an internal Docker network.

version: '3'

services:
  frontend:
    image: react-app

  backend:
    image: node-app

  database:
    image: mongo

 In this example:

• frontend runs the React application
• backend runs the Node.js API
• database runs MongoDB

All services are automatically connected through an internal Docker network. Learn Docker Compose, deploy React and Node.js applications, and master container troubleshooting with practical examples. A beginner-friendly guide for DevOps and System Engineers.

Starting Docker Compose

Run:

• docker compose up

Docker will:

• Create networks
• Create containers
• Start services
• Connect containers

To run in the background:

• docker compose up -d
• Stopping Docker Compose

Stop all services:

• docker compose down

Docker removes containers and networks created by Compose.

 Deploying a React Application

  
FROM node:22

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

EXPOSE 3000

CMD ["npm","start"]
  

Build the image:

• docker build -t react-app .

Run the container:

• docker run -d -p 3000:3000 react-app

Open:

• http://localhost:3000

Your React application should now be accessible.

Deploying a Node.js Application

Create a Dockerfile:

Build the image:

  
  FROM node:22

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

EXPOSE 5000

CMD ["node","server.js"]
  

• docker build -t node-app .

Run the application:

• docker run -d -p 5000:5000 node-app

Access:

• http://localhost:5000

Deploying React, Node.js, and MongoDB Together

A production application often contains:



Docker Compose makes managing these services much easier.

Example:

React Frontend
       │
       ▼
Node.js Backend
       │
       ▼
MongoDB Database

 
Start everything:

docker compose up -d

Now all services run together.

version: '3'

services:
  frontend:
    image: react-app
    ports:
      - "3000:3000"

  backend:
    image: node-app
    ports:
      - "5000:5000"

  mongodb:
    image: mongo
    ports:
      - "27017:27017"

Container Troubleshooting

Troubleshooting is an essential Docker skill for System Engineers and DevOps Engineers.

Check Running Container

• docker ps

View all containers:

• docker ps -a 

Check Container Logs

Logs help identify startup issues.

docker logs container_name

Example:

• docker logs backend

Access Container Shell

Enter a running container:

• docker exec -it container_name bash

Example:

• docker exec -it backend bash

This is useful for checking:

• Application files
• Environment variables
• Network connectivity
• Installed packages

Inspect Container Details

View container configuration:

docker inspect container_name

This displays:

• IP Address
• Volumes
• Networks
• Environment Variables
• Mount Points
• Monitor Resource Usage

Check CPU and Memory:

• docker stats

Useful for identifying performance bottlenecks.

 Restart a Container

docker restart container_name

Example:

• docker restart backend

Common Docker Issues

Port Already in Use

Error:

• Bind for 0.0.0.0 failed

Solution:

• docker ps

Find the conflicting container and stop it.

Container Exits Immediately

Check logs:

• docker logs container_name

Usually caused by:

• Incorrect CMD
• Missing dependencies
• Application errors
• Cannot Access Application

Verify:

• docker ps

Check:

• Port mapping
• Firewall settings
• Container status 

Network Communication Issues

Inspect network:

• docker network ls
• Inspect container:
• docker inspect container_name
• Ensure containers are connected to the same Docker network.

Essential Commands

Start Compose:

• docker compose up -d
• Stop Compose:
• docker compose down
• View Containers:
• docker ps
• View Logs:
• docker logs container_name
• Enter Container:
• docker exec -it container_name bash
• Inspect Container:
• docker inspect container_name
• Monitor Resources:
• docker stats

Conclusion

Docker Compose simplifies the management of multi-container applications by allowing developers and system administrators to define services in a single configuration file.

Combined with React, Node.js, and MongoDB deployments, Docker Compose enables efficient application management and scalable infrastructure. Understanding container troubleshooting techniques further prepares you for real-world DevOps, Cloud Engineering, and System Administration roles.

Mastering Docker Compose and troubleshooting skills is a significant step toward becoming a proficient System Engineer or DevOps Engineer.

Docker Networking 

Docker networks allow containers to communicate with each other.

Example :

Frontend Container
        │
        ▼
Backend Container
        │
        ▼
Database Container
  

Without networking:

❌ Containers cannot easily communicate.

With networking:

✅ Containers communicate securely.



In docker networks there are 6 types of networks - 

1) bridge
2) host
3) overlay
4) ipvlan
5) macvlan
6) none


so steps by steps we will learn each and every docker networks.


1. Bridge - Its a default network as a bridge and if we will make container and don't make any other networks so its use by default network as a bridge from our host machine.

So let's see how to verify we have connected through bridge while making container.  if you are followed our docker's blog continuously then you know we have already images ,  container that we are already uploaded.

So, here we will run our docker desktop from our system (in windows search bar search docker desktop) are using our first command  

• docker run -it --name server1 ubuntu bash

Here:

• server1  = Container Name
• ubuntu   = Image Name
• bash     = Command to run

Here a ubuntu server is running even you can verify container name via 

• docker ps

Lets verify this docker container is connected via internet.

So as you can see the old one images and in that container we are facing some problems to apt-get or apt install iputils-ping -y because we are unable to use ping command.

So we will create new one file, docker images and install manually so follow the steps and do with scratch. 

Step 1: Create a folder

networking-dev/
├── Dockerfile

Step 2: Create Dockerfile

So go to your desire directory in your local machine and then create a folder

mkdir networking-dev

cd networking-dev  

and inside the folder open vs code editor  so type a file name without any extension.

code Dockerfile 

add this command and save it simple.

FROM ubuntu:24.04

RUN apt-get update && \
    apt-get install -y \
    iputils-ping \
    net-tools \
    iproute2 \
    dnsutils

CMD ["bash"]

This installs:

ping
ifconfig
ip
nslookup
other networking tools

Step 3: Build your image

Go inside the folder containing the Dockerfile: 

• docker build -t atul/networking-dev .

 
Notice the . at the end.

Docker will:

• Read the Dockerfile
• Download Ubuntu 24.04
• Install ping, net-tools, iproute2, dnsutils
• Create image atul/networking-dev

Verify:

docker images

You should see:

REPOSITORY           TAG
atul/networking-dev  latest

Run container

Now lets move into our real purpose of this blog docker networking via bridge

So, here we will run our docker desktop from our system (in windows search bar search docker desktop) are using our first command  

• docker run -it --name server1 atul/networking-dev

Previously we have server1 in container docker desktop so delete it. 

Inside container test:

ping google.com
ifconfig
ip addr
nslookup google.com

All should work.

• docker ps 

C:\Users\user\Desktop\app>docker ps
CONTAINER ID   IMAGE                 COMMAND   CREATED         STATUS         PORTS     NAMES
98acba8d0340   atul/networking-dev   "bash"    4 minutes ago   Up 4 minutes             server1

C:\Users\user\Desktop\app>

Verify which network a container is using

Run:

• docker inspect server1

Large output will appear.

To see only network information:

• docker inspect server1 --format='{{json .NetworkSettings.Networks}}'

Output:

{"bridge":{"IPAddress":"172.17.0.1"}}

This means:

Container: server1
Network: bridge
IP: 172.17.0.1

Practical Demo

Create two containers:

• docker run -dit --name server1  atul/networking-dev
• docker run -dit --name server2  atul/networking-dev

Check:

docker ps

After creating server in another terminal lets check IP address even try to ping each other

hostname -I 

ping 172.17.0.2 

We are able because both are connected with docker network by default bridge.

Enter server1:

docker exec -it server1 bash

Try:

ping server2

On the default bridge network, name resolution may not work as expected.

root@98acba8d0340:/# ping server2
ping: server2: Name or service not known
root@98acba8d0340:/#

we are not able to ping because of they are only default network as an IP address.

 A better practice is creating your own network: so for this open new terminal and run this command 

• docker network create mynetwork

open another terminal and type this command with server3 and --network mynetwork

hostname -I 

you can see the IP there is -  172.18.0.2 but this is in another class - 18 and previous one are in 17 class

Now we want to connect server 1 with my network mynetwork

and you can see in server1 having two different class IP

now we are able to run using name 

These are commands that we have used 

docker network ls
docker inspect server1
docker network create mynetwork
docker run --network mynetwork ...

Conclusion

Understanding Dockerfiles, custom image creation, and environment variables is essential for anyone learning Docker, DevOps, Cloud Computing, or System Administration.

By mastering these concepts, you'll be able to create reusable Docker images, automate deployments, and configure applications efficiently. These skills are widely used in real-world production environments and are frequently asked about in DevOps and System Engineer interviews.

Docker Volumes

What is a Docker Volume?

A Docker Volume is used to store data permanently, even if the container is deleted.


Without a volume:

Container Deleted
      ↓
Data Deleted
  

With a volume:

Container Deleted
      ↓
Data Remains Safe  

Why Do We Need Volumes?

Imagine a MySQL container:

• docker run mysql

All database data is inside the container.


If the container is removed:

• docker rm mysql-container

Your database is gone. 

Docker local file to docker container

How to use docker volume inside the docker ?


First we will create a file or file with code in local machine and then mount with docker and run nodejs code with nodemon and we will see live code's output in docker.

In our local machine --> go to desktop --> creating new folder --> then open in vs code --> then mount it

• cd Desktop
• mkdir app
• code app

Mount it 

• docker run -it node:latest

 Now we will mount from in our local machine's folder that we have created a folder name is app wtih node folder. so for this you can check our folder is there - docker container ls -a 

 use this command - docker run -it -v 

• -it -> interactive mode
• -v -> volume (with which you can attach any volume from your own machine to our docker container).
• copy of address of my folder 
• :   -> then mount with my container's address 

then you can see the above image and if we type uname there is linux and we will go docker container's directory cd home then ls for list directory.

 cd app

ls

there is a file called index.js  

index.js file is coming from our local machine. 

 you can check here cat index.js 

Now we will nodemon in our container and will run our node js file and if we try to change from our local machine then it will effect in our container where as we did run nodemon index.js file.

so first we will install nodemon as a globally.

npm install -g nodemon

then we will run nodemon index.js  

 if we change anything in our file index.js in our local machine then it will changes effect here because both are pointing same memory location and so if you are unable to changes anything as a output so run this command.

nodemon -L index.js 

Second way to create docker volume

This is the way to mount any file to docker container and now we will try to create a docker volume so for this  type this command and as well as open docker desktop that we have installed in previous blog article - check out Here - 

CLICK HERE

docker volume create data 

data -> is the name of volume 

Now you can check here if we type this command - docker volume ls

here it is showing  local as a our Driver local machine 

and

Volume name as a data that we have created just now 

Now we will attach our data volume to our docker container 

use this command - 

docker run -it -v data:/data node bash 

Here you can check here is a folder called as data so go to this data folder and again type ls command and nothing is there 

so we will create a file or folder atul.js for data volume and you can use this command mkdir atul.js and type again ls atul.js

so now we can say that what we have created a data volume that its attached with our local file. so for this you see this

open another terminal and type this command - 

docke run -it -v data:/myapp ubuntu 

go to this this directory

cd myapp

ls

and you can see that there is same atul.js is there   

lets say if we create a another file or folder in previous container terminal so we are able to see in another same file in our data volume because we have create a volume called as data and each and every container file pushed in volume data.

Conclusion

Understanding Dockerfiles, custom image creation, and environment variables is essential for anyone learning Docker, DevOps, Cloud Computing, or System Administration.

By mastering these concepts, you'll be able to create reusable Docker images, automate deployments, and configure applications efficiently. These skills are widely used in real-world production environments and are frequently asked about in DevOps and System Engineer interviews.

How to identify my wbs chargecode in powershell

A WBS (Work Breakdown Structure) / Charge code is usually not something Powershell can 'discover' automatically from your system because it's company-specific financial/project data (Stored in tools like SAP, ServiceNow, internal portals, or time-tracking systems).

1. Check Environment Variables (if your organization uses them)

Some companies push project/charge codes as environment variables.

Get-ChildItem Env:

Look for anything like:

• WBS
• CHARGECODE
• PROJECT
• COSTCENTER

2. Check Active Directory (if stored in AD)

Sometimes WBS/cost center is stored as a user attribute.

Get-ADUser -Identity $env:USERNAME -Properties *

Look for fields like:

• department
• extensionAttributeX
• employeeID
• costCenter

Filter only relevant fields:

Get-ADUser -Identity $env:USERNAME -Properties  department,extensionAttribute1,extensionAttribute2

If you got error like as you can see the image below so in screenshot, the error is very clear:

Get-ADUser : The term 'Get-ADUser' is not recognized

✅ What this means

Your PowerShell does not have the Active Directory module installed or loaded.

Get-ADUser comes from the ActiveDirectory module, which is:

• ✅ Available on domain-joined machines with RSAT installed
• ❌ Not available by default on normal Windows installs

✅ Fix it (step-by-step)

🔹 Option 1: Check if module exists but not loaded

Get-Module -ListAvailable ActiveDirectory

👉 If you see output well and good but if you are not seeing then leave it as of now.

Then just import it:

Import-Module ActiveDirectory

Option 2: Install RSAT (Most likely needed)

Since you’re a IT Support Engineer, this is probably your case.

Run:

Get-WindowsCapability -Name RSAT.ActiveDirectory* -Online

Install it:

Add-WindowsCapability -Online -Name RSAT.ActiveDirectory.DS-LDS.Tools~~~~0.0.1.0

Option 3: If installation is blocked

In many corporate environments:

❌ You may NOT have permission to install RSAT

👉 Then:

Ask IT:

"Please enable RSAT Active Directory PowerShell module on my machine"

✅ After fixing

Use this correct command 

👉 Environment variables cannot start with numbers

✅ Correct version:

If your username is your ID:

Get-ADUser -Identity $env:USERNAME -Properties *

Or explicitly:

Get-ADUser -Identity 221843 -Properties *

Filter WBS / Charge info (after it works)

Get-ADUser -Identity $env:USERNAME -Properties * |
Select-Object Name, Department, Title, extensionAttribute1, extensionAttribute2

Disclaimer