Network Architecture

13 min read

Updated Jun 19, 2025

Network Architecture Overview

A well-designed network architecture is the foundation of secure, scalable, and resilient infrastructure. This guide covers enterprise network design patterns, security considerations, and implementation best practices for modern cloud and hybrid environments.

Prerequisites: Understanding of TCP/IP, subnetting, routing protocols, and basic security concepts. Familiarity with cloud networking services (AWS VPC, Azure VNet, GCP VPC) is recommended.

Core Network Design Principles

1. Defense in Depth

Implement multiple layers of security controls throughout your network:

Perimeter Security: Firewalls, IDS/IPS, DDoS protection
Network Segmentation: VLANs, subnets, security groups
Access Control: NACLs, security groups, microsegmentation
Encryption: TLS/SSL, IPSec VPNs, encrypted tunnels
Monitoring: Flow logs, packet capture, anomaly detection

2. Zero Trust Architecture

# Zero Trust Network Principles:
1. Never trust, always verify
2. Assume breach - design for compromise
3. Verify explicitly - authenticate and authorize every transaction
4. Use least privilege access
5. Inspect and log all traffic

3. Scalability and Performance

Horizontal Scaling: Design for distributed load across multiple paths
Redundancy: No single points of failure
Caching: Strategic placement of caching layers
CDN Integration: Global content distribution
Traffic Engineering: QoS, traffic shaping, load balancing

Virtual Private Cloud (VPC) Architecture

Multi-Tier VPC Design

# Example: AWS VPC with public/private/database tiers

VPC CIDR: 10.0.0.0/16

Public Subnets (Internet-facing):
- us-east-1a: 10.0.1.0/24
- us-east-1b: 10.0.2.0/24
- us-east-1c: 10.0.3.0/24

Private Subnets (Application tier):
- us-east-1a: 10.0.11.0/24
- us-east-1b: 10.0.12.0/24
- us-east-1c: 10.0.13.0/24

Database Subnets (Data tier):
- us-east-1a: 10.0.21.0/24
- us-east-1b: 10.0.22.0/24
- us-east-1c: 10.0.23.0/24

Management Subnets (Bastion/VPN):
- us-east-1a: 10.0.31.0/24

Network Access Control Lists (NACLs)

Implement stateless subnet-level security:

# Public Subnet NACL
Rule | Type    | Protocol | Port Range | Source      | Allow/Deny
100  | Inbound | TCP      | 80         | 0.0.0.0/0   | ALLOW
110  | Inbound | TCP      | 443        | 0.0.0.0/0   | ALLOW
120  | Inbound | TCP      | 22         | 10.0.31.0/24| ALLOW
200  | Inbound | TCP      | 1024-65535 | 0.0.0.0/0   | ALLOW
*    | Inbound | ALL      | ALL        | 0.0.0.0/0   | DENY

# Private Subnet NACL
Rule | Type    | Protocol | Port Range | Source      | Allow/Deny
100  | Inbound | TCP      | 3000-3100  | 10.0.1.0/23 | ALLOW
110  | Inbound | TCP      | 22         | 10.0.31.0/24| ALLOW
*    | Inbound | ALL      | ALL        | 0.0.0.0/0   | DENY

Security Groups

Stateful instance-level firewalls with explicit allow rules:

# Web Server Security Group
resource "aws_security_group" "web_sg" {
  name_prefix = "web-servers-"
  vpc_id      = aws_vpc.main.id

  ingress {
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
    description = "HTTPS from anywhere"
  }

  ingress {
    from_port       = 22
    to_port         = 22
    protocol        = "tcp"
    security_groups = [aws_security_group.bastion_sg.id]
    description     = "SSH from bastion only"
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
    description = "Allow all outbound"
  }

  lifecycle {
    create_before_destroy = true
  }
}

Hybrid Cloud Networking

Site-to-Site VPN Configuration

Connect on-premises networks to cloud VPCs:

# IPSec VPN Configuration Example
Customer Gateway:
- IP Address: 203.0.113.10
- BGP ASN: 65000
- Routing: Dynamic (BGP) or Static

Virtual Private Gateway:
- Amazon Side ASN: 64512
- Attached to VPC: vpc-12345678

VPN Connection:
- Tunnel 1: 169.254.10.0/30 (Inside IP CIDR)
- Tunnel 2: 169.254.11.0/30 (Inside IP CIDR)
- Pre-shared Keys: Generate unique 64-character keys
- DPD Timeout: 30 seconds
- IKE Version: IKEv2

# strongSwan Configuration (Customer Side)
conn AWS-VPC-TUNNEL-1
    type=tunnel
    auto=start
    keyexchange=ikev2
    ike=aes256-sha256-modp2048
    esp=aes256-sha256
    ikelifetime=28800s
    lifetime=3600s
    dpddelay=30s
    dpdtimeout=120s
    dpdaction=restart
    left=%defaultroute
    leftid=203.0.113.10
    leftsubnet=192.168.0.0/16
    right=52.84.123.45
    rightsubnet=10.0.0.0/16
    authby=secret

AWS Direct Connect / Azure ExpressRoute

Dedicated network connections for predictable performance:

Bandwidth Options: 50 Mbps to 100 Gbps
VLAN Support: 802.1Q VLAN tagging
BGP Routing: Dynamic route advertisement
Redundancy: Multiple connections across different locations
Virtual Interfaces: Multiple VIFs per physical connection

Transit Gateway Architecture

# Hub-and-Spoke Network Topology
Transit Gateway (TGW):
- Region: us-east-1
- ASN: 64512
- Default Route Table: Enabled
- DNS Support: Enabled
- Multicast Support: Disabled

Attachments:
1. Production VPC (10.1.0.0/16)
2. Development VPC (10.2.0.0/16)
3. Shared Services VPC (10.3.0.0/16)
4. VPN Connection (On-premises)
5. Direct Connect Gateway

Route Tables:
- Production Routes: 0.0.0.0/0 → NAT Gateway
- Dev Routes: 10.0.0.0/8 → Local
- On-Prem Routes: 192.168.0.0/16 → VPN

Load Balancing Architecture

Application Load Balancer (Layer 7)

# ALB Configuration with SSL/TLS
resource "aws_lb" "application" {
  name               = "app-alb"
  internal           = false
  load_balancer_type = "application"
  security_groups    = [aws_security_group.alb_sg.id]
  subnets           = aws_subnet.public[*].id

  enable_deletion_protection = true
  enable_http2              = true
  enable_cross_zone_load_balancing = true

  access_logs {
    bucket  = aws_s3_bucket.alb_logs.bucket
    prefix  = "alb"
    enabled = true
  }
}

# HTTPS Listener with SSL Policy
resource "aws_lb_listener" "https" {
  load_balancer_arn = aws_lb.application.arn
  port              = "443"
  protocol          = "HTTPS"
  ssl_policy        = "ELBSecurityPolicy-TLS-1-2-2017-01"
  certificate_arn   = aws_acm_certificate.cert.arn

  default_action {
    type = "forward"
    target_group_arn = aws_lb_target_group.app.arn
  }
}

# Path-based routing
resource "aws_lb_listener_rule" "api" {
  listener_arn = aws_lb_listener.https.arn
  priority     = 100

  action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.api.arn
  }

  condition {
    path_pattern {
      values = ["/api/*"]
    }
  }
}

Network Load Balancer (Layer 4)

For high-performance, low-latency requirements:

Ultra-low latency: Single-digit millisecond latency
Static IP addresses: Elastic IPs per AZ
Preserve source IP: No proxy protocol needed
Million+ requests/second: Extreme performance
TLS termination: Optional TLS offload

Global Load Balancing

# Route 53 Geolocation Routing
resource "aws_route53_record" "www" {
  zone_id = aws_route53_zone.primary.zone_id
  name    = "www.example.com"
  type    = "A"

  set_identifier = "US"
  geolocation_routing_policy {
    continent = "NA"
  }

  alias {
    name                   = aws_lb.us_east_1.dns_name
    zone_id                = aws_lb.us_east_1.zone_id
    evaluate_target_health = true
  }
}

# Health checks
resource "aws_route53_health_check" "primary" {
  fqdn              = aws_lb.us_east_1.dns_name
  port              = 443
  type              = "HTTPS"
  resource_path     = "/health"
  failure_threshold = "3"
  request_interval  = "30"
}

Network Security Best Practices

WAF Implementation

# AWS WAF Rules
{
  "Name": "RateLimitRule",
  "Priority": 1,
  "Statement": {
    "RateBasedStatement": {
      "Limit": 2000,
      "AggregateKeyType": "IP",
      "ScopeDownStatement": {
        "ByteMatchStatement": {
          "SearchString": "/api/",
          "FieldToMatch": {
            "UriPath": {}
          },
          "TextTransformations": [{
            "Priority": 0,
            "Type": "NONE"
          }],
          "PositionalConstraint": "STARTS_WITH"
        }
      }
    }
  },
  "Action": {
    "Block": {
      "CustomResponse": {
        "ResponseCode": 429,
        "CustomResponseBodyKey": "rate-limit-exceeded"
      }
    }
  }
}

DDoS Protection

AWS Shield Standard: Automatic protection against common attacks
AWS Shield Advanced: Enhanced DDoS protection with 24x7 DRT support
CloudFlare: Global anycast network with DDoS mitigation
Rate Limiting: API Gateway throttling, WAF rate rules
Auto Scaling: Absorb traffic spikes automatically

Network Monitoring and Logging

# VPC Flow Logs Configuration
resource "aws_flow_log" "vpc_flow_log" {
  iam_role_arn    = aws_iam_role.flow_log.arn
  log_destination = aws_cloudwatch_log_group.flow_log.arn
  traffic_type    = "ALL"
  vpc_id          = aws_vpc.main.id

  tags = {
    Name = "vpc-flow-logs"
  }
}

# Sample Flow Log Entry
2 123456789010 eni-abc123de 172.31.16.139 172.31.16.21 20641 22 6 20 4249 1418530010 1418530070 ACCEPT OK

# Fields: version account-id interface-id srcaddr dstaddr srcport dstport protocol packets bytes start end action log-status

Content Delivery Network (CDN) Architecture

CloudFront Distribution

# CloudFront with S3 Origin
resource "aws_cloudfront_distribution" "cdn" {
  enabled             = true
  is_ipv6_enabled     = true
  default_root_object = "index.html"
  price_class         = "PriceClass_All"

  origin {
    domain_name = aws_s3_bucket.static_assets.bucket_regional_domain_name
    origin_id   = "S3-${aws_s3_bucket.static_assets.id}"

    s3_origin_config {
      origin_access_identity = aws_cloudfront_origin_access_identity.oai.cloudfront_access_identity_path
    }
  }

  origin {
    domain_name = aws_lb.application.dns_name
    origin_id   = "ALB-${aws_lb.application.id}"

    custom_origin_config {
      http_port              = 80
      https_port             = 443
      origin_protocol_policy = "https-only"
      origin_ssl_protocols   = ["TLSv1.2"]
    }
  }

  default_cache_behavior {
    allowed_methods  = ["GET", "HEAD", "OPTIONS"]
    cached_methods   = ["GET", "HEAD"]
    target_origin_id = "ALB-${aws_lb.application.id}"

    forwarded_values {
      query_string = true
      cookies {
        forward = "none"
      }
      headers = ["Host", "Accept", "Accept-Language", "CloudFront-Viewer-Country"]
    }

    viewer_protocol_policy = "redirect-to-https"
    min_ttl                = 0
    default_ttl            = 86400
    max_ttl                = 31536000
    compress               = true
  }

  # Static assets behavior
  ordered_cache_behavior {
    path_pattern     = "/static/*"
    allowed_methods  = ["GET", "HEAD"]
    cached_methods   = ["GET", "HEAD"]
    target_origin_id = "S3-${aws_s3_bucket.static_assets.id}"

    forwarded_values {
      query_string = false
      cookies {
        forward = "none"
      }
    }

    viewer_protocol_policy = "redirect-to-https"
    min_ttl                = 86400
    default_ttl            = 604800
    max_ttl                = 31536000
    compress               = true
  }

  restrictions {
    geo_restriction {
      restriction_type = "none"
    }
  }

  viewer_certificate {
    acm_certificate_arn = aws_acm_certificate_validation.cert.certificate_arn
    ssl_support_method  = "sni-only"
  }
}

Network Troubleshooting Guide

Common Network Issues

Issue	Symptoms	Diagnosis	Resolution
Connectivity Failure	Cannot reach instances	Check Security Groups, NACLs, Route Tables	Update rules, verify routes
High Latency	Slow response times	Traceroute, MTR, Flow Logs	Optimize routing, use CDN
Packet Loss	Intermittent failures	Ping tests, packet capture	Check bandwidth, QoS settings
DNS Resolution	Name resolution fails	nslookup, dig commands	Verify DNS settings, TTLs

Diagnostic Commands

# Network connectivity test
$ nc -zv hostname 443
Connection to hostname 443 port [tcp/https] succeeded!

# DNS troubleshooting
$ dig +trace example.com

# Path MTU discovery
$ ping -M do -s 1472 hostname

# TCP connection analysis
$ ss -tan | grep ESTABLISHED

# Packet capture for deep analysis
$ tcpdump -i eth0 -w capture.pcap port 443

# AWS VPC Reachability Analyzer
$ aws ec2 create-network-insights-path \
    --source i-0123456789abcdef0 \
    --destination i-0fedcba9876543210 \
    --protocol tcp \
    --destination-port 443