Designing a Secure Network

This final lesson brings together all the concepts from the course into a practical framework for designing a secure network from the ground up. Whether you are building a new network or re-architecting an existing one, the process follows the same structured approach.

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The Design Process

Phase	Activity	Output
1. Requirements Gathering	Understand business needs, compliance, and risk appetite	Requirements document
2. Asset and Data Classification	Identify what needs protecting and its sensitivity	Asset register, data classification
3. Architecture Design	Create the network topology, zones, and control placement	Architecture diagrams
4. Control Selection	Choose specific security controls for each layer	Control matrix
5. Implementation	Build the network according to the design	Configured infrastructure
6. Validation	Test through penetration testing and review	Validation report
7. Operations	Monitor, maintain, and continuously improve	Operational procedures

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Phase 1: Requirements Gathering

Business Requirements

Requirement	Questions to Ask
Users	How many users? Where are they located? Remote or on-site?
Applications	What applications must be accessible? Internal or external?
Performance	What throughput, latency, and availability levels are required?
Growth	What is the expected growth over 3-5 years?
Budget	What is the available budget for security infrastructure?

Compliance Requirements

Standard	Key Network Requirements
PCI DSS	Segmentation of cardholder data environment, firewall rules, logging
ISO 27001	Documented network security policy, access controls, monitoring
HIPAA	Encryption of health data in transit, access controls, audit logging
GDPR	Data protection by design, encryption, access controls
SOC 2	Logical access controls, monitoring, incident response

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Phase 2: Asset and Data Classification

Data Classification Levels

Level	Description	Example	Controls Required
Public	No impact if disclosed	Marketing materials	Basic availability
Internal	Minor impact if disclosed	Internal policies	Access controls
Confidential	Significant impact if disclosed	Customer data, financial records	Encryption, strict access, DLP
Restricted	Severe impact if disclosed	Passwords, cryptographic keys, health records	Maximum controls, audit logging

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Phase 3: Architecture Design

Reference Architecture

                         Internet
                            │
                            ▼
                    [DDoS Mitigation]
                            │
                            ▼
                    [Border Router / ACLs]
                            │
                            ▼
                    [External Firewall]
                            │
               ┌────────────┼────────────┐
               │            │            │
               ▼            ▼            ▼
          [DMZ Zone]   [VPN Gateway]  [Email GW]
          Web, DNS     Remote Access  Mail Relay
               │            │            │
               └────────────┼────────────┘
                            │
                    [Internal Firewall]
                            │
          ┌─────────────────┼─────────────────┐
          │                 │                 │
          ▼                 ▼                 ▼
    [User Zone]      [Server Zone]     [Management Zone]
    Workstations     App + DB Servers   Network Mgmt
          │                 │                 │
          └─────────────────┼─────────────────┘
                            │
                    [SIEM / Monitoring]
                    (collects from all zones)

Zone Design Decisions

Zone	Purpose	Key Controls
DMZ	Public-facing services	NGFW, WAF, IDS/IPS, hardened servers
User Zone	Employee workstations	NAC (802.1X), EDR, DNS filtering
Server Zone	Application and database servers	Microsegmentation, encryption, access controls
Management Zone	Network device administration	Jump box, PAM, MFA, strict ACLs
Guest Zone	Visitor internet access	Isolated VLAN, captive portal, no internal access
IoT Zone	Cameras, sensors, smart devices	Dedicated VLAN, strict ACLs, monitoring
Cloud Zone	Cloud workloads	VPC, security groups, flow logs, CSPM

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Phase 4: Control Selection

Control Matrix