Networking on My IT Journal

DMZ Network Lab - Firewall, Routing, and nftables

Tue, 16 Jun 2026 00:00:00 +0000

Objective

The goal of this lab is to design and implement a basic DMZ (Demilitarized Zone) network using Linux virtual machines, understand routing between network segments, and apply nftables as a stateful firewall.

Network Topology

LAN (User Network)		DMZ (Service Network)
192.168.10.0/24			192.168.20.0/24
__________________		_____________________

Client VM			Server VM
192.168.10.101			192.168.20.10
	|				|
	|				|
	________ Firewall VM ___________
		(Router + Firewall)

VM & Routing Configuration

Client VM

sudo netplan try
sudo netplan apply

Firewall VM (Core Router)

Linux nftables Firewall Fundamentals Lab

Mon, 15 Jun 2026 00:00:00 +0000

Objective

Lab Environment

Client VM 1 - 192.168.10.101 Client VM 2 - 192.168.10.102 Server VM - 192.168.10.10

Server Setup

Step 1 - Run web server

python3 -m http.server 8080
ss -tln | grep :8080

Step 2 - Base firewall configuration

sudo nft add table inet filter
sudo nft add chain inet filter input \
'{ type filter hook input priority 0; policy drop; }'
sudo nft add rule inet filter input iif lo accept
sudo nft add rule inet filter input ct state established,related accept

DHCP Lab: Setup, Failure Scenarios & Debugging Workflow

Thu, 23 Apr 2026 00:00:00 +0000

🧪 DHCP Lab

📌 Objective

Understand how DHCP works in real network environment and how to debug common failure scenarios using a structured top-to-bottom approach.

⚙️ Environment

Virtualization: VirtualBox
OS: Ubuntu Server (1 DHCP Server VM & 2 Client VMs)
Network mode: Internal Network + NAT (enp0s3 ignored for DHCP lab)

🛠️ Network Setup

Interfaces

DHCP Server

enp0s8 -> 192.168.10.10/24 (Lab network)
enp0s3 -> NAT

Clients

enp0s8 -> DHCP assigned IPs
enp0s3 -> NAT (not used)

⚙️ Network Configuration (Netplan)

Both server and clients are configured using Netplan, which defines interface behavior before DHCP starts.

Basic Network Setup & Connectivity

Wed, 22 Apr 2026 00:00:00 +0000

🧪 Basic Network Setup & Connectivity Lab

📌 Objective

Understand how IP addressing, subnetting, and basic connectivity work in a controlled virtual environment.

⚙️ Environment

Virtualization: VirtualBox
OS: Ubuntu Server (2 VMs)
Network mode: Internal Network + NAT

VMs

VM	IP Address	Role
VM1	192.168.10.10/24	Client
VM2	192.168.10.20/24	Server

🛠️ Setup

Step 1 - Create Virtual Machines

Create two Linux virtual machines:

server_01
server_02

Recommended specs:

1 CPU
1-2 GB RAM
10+ GB disk

Step 2 - Configure Network

Both VMs must use the same Internal Network This ensures both machines are on the same isolated Layer 2 network.