Linux Network Infrastructure Automation

Context

This project represents a complete refactoring of a first-year university networking assignment. While the initial topology was designed in a pair programming setting, I rebuilt the entire implementation individually to modernize the deployment process.

I replaced the original manual configuration steps with robust, idempotent Bash scripts, demonstrating Infrastructure as Code (IaC) practices to ensure consistency and reliability.

Architecture Overview

The infrastructure simulates a segmented corporate network using Debian virtual machines, divided into two security zones:

1. VLAN Zone (ID 117): Isolated internal network for Client workstations and the DHCP Server.
2. LAN Zone (Management): Host for core services including the SMTP Mail Server and DNS Authority.
3. Router Node: A central gateway managing NAT (Masquerade), Stateful Firewall rules (iptables), and inter-VLAN routing.

Technical Implementation

Automation & Scripting

I developed a unified orchestration script (network-config.sh) that automates the provisioning of any node in the network.

• Idempotency: The script uses checks (e.g., iptables -C, ip link show) to prevent duplicate configurations, allowing safe re-execution.
• Persistence: It configures netfilter-persistent and sysctl.d to ensure routing tables and security rules survive system reboots.
• Dynamic Config: It automatically generates configuration files for isc-dhcp-server and postfix based on the environment variables.

Network Analysis

To validate the integrity of the network, I performed deep packet analysis using Wireshark:

• Verified 802.1Q VLAN tagging in ICMP frames.
• Analyzed the 4-step DHCP DORA handshake (Discover, Offer, Request, Acknowledge).
• Traced DNS resolution and TCP handshakes for SMTP traffic.

Key Outcomes

• Transitioned from manual, error-prone setup to a single-command deployment.
• Implemented Stateful Firewalling to allow established return traffic while blocking unauthorized access.
• Produced professional technical documentation and architectural diagrams.