Raspberry Pi 3B+ Platform Capabilities

Feature set, performance metrics, and technical capabilities of RPi 3B+ for home and small office routing

Raspberry Pi 3B+ Platform Capabilities

The Raspberry Pi 3B+ provides reliable routing and networking features for home and small office environments. This document details the technical capabilities and realistic performance characteristics of this legacy platform.

Platform Architecture

Core Computational Design

The RPi 3B+ is built on a proven architecture suitable for basic to moderate routing operations:

CPU Architecture:

  • Quad-core ARM Cortex-A53 (ARMv8-A)
  • 1.4 GHz clock speeds
  • 64-bit instruction set support with 32-bit compatibility
  • ~1,800 DMIPS multi-threaded performance
  • Software-only cryptographic operations (no hardware acceleration)

Memory Design:

  • 1GB LPDDR2 SDRAM @ 900 MHz
  • ~7 GB/s memory bandwidth
  • Unified CPU/GPU memory with configurable split
  • Suitable for home and small office routing
  • Limited headroom for advanced features

Network Architecture:

  • Gigabit Ethernet controller via USB 2.0 bus
  • ~300 Mbps practical throughput (bus limitation)
  • Shared bandwidth between Ethernet and USB ports
  • 802.11ac dual-band Wi-Fi (Cypress CYW43455)
  • Bluetooth 4.2 with BLE

Key Limitation: The Ethernet controller shares the USB 2.0 bus with all USB ports, creating a performance ceiling around 300 Mbps for routing operations.

Network Throughput Performance

Routing Performance Capabilities

The RPi 3B+ provides suitable routing performance for home and small office networks:

Basic Routing (with standard Linux kernel):

  • Throughput: Suitable for broadband connections up to the USB 2.0 bus limitation
  • Packet Handling: Capable of processing typical home network traffic patterns
  • Latency: Low latency under normal load conditions
  • Configuration: Efficient nftables/iptables firewall processing

With Filtering and QoS:

  • Throughput: Maintains good performance with DNS filtering and content blocking enabled
  • DNS Filtering: Effective ad-blocking and malware protection with minimal impact
  • Basic QoS: Traffic shaping supported with moderate throughput overhead
  • Performance Margin: Suitable for typical home/small office feature requirements

VPN Server Mode:

  • WireGuard: Suitable for moderate VPN workloads
  • OpenVPN: Supported for compatibility needs
  • Concurrent Clients: Supports multiple simultaneous VPN connections
  • Limitation: CPU-bound due to lack of hardware crypto acceleration

Standard Feature Stack (typical home/small office):

  • Throughput: Appropriate for home broadband and small office internet connections
  • Configuration: Basic VPN + firewall + DNS filtering + monitoring
  • Scalability: Best suited for internet connections within the platform's bus architecture limits
  • Reliability: Stable performance within design constraints

Connection Handling Capacity

Concurrent Connection Support

The RPi 3B+ platform efficiently manages moderate numbers of simultaneous network connections suitable for home and small office deployments:

TCP Connections:

  • Capacity: Supports thousands of established connections
  • Optimal Range: Best performance with typical home/small office connection loads
  • Small Network: Suitable for small networks with dozens of devices
  • Home Network: Appropriate for typical home networks with many connected devices
  • Memory Consideration: Connection tracking is memory-efficient

DHCP Client Support:

  • Capacity: Handles typical home and small office DHCP pool sizes
  • Lease Management: Efficient pool handling
  • Typical Deployment: Well-suited for standard home/office client counts
  • Scalability: Appropriate for environments within the 1GB memory constraint

DNS Query Performance:

  • Query Rate: Handles typical DNS query loads for home and small office networks
  • Concurrent Queries: Efficient parallel query processing
  • Cache Capacity: Configurable cache size appropriate for typical usage patterns
  • Memory for Cache: Scalable cache within available memory limits
  • DNSSEC Validation: Supported with expected cryptographic overhead

Firewall Rules:

  • Rule Capacity: Supports extensive firewall rule sets
  • Processing: Efficient rule matching for typical configurations
  • Types: Stateful and stateless rules supported
  • Matching Speed: Software-based packet filtering

Memory Configuration Analysis

Single 1GB Configuration

The RPi 3B+ has a fixed 1GB LPDDR2 memory configuration requiring careful resource management:

Typical Memory Allocation:

Base Operating System:    230 MB (23%)
Pimeleon Router Core:      65 MB (7%)
Network Buffers:          300 MB (30%)
Connection State Table:   100 MB (10%)
DNS Cache:               50-100 MB (5-10%)
Available for Growth:    200-300 MB (20-30%)

Memory Constraints:

  • Total Available: ~1024 MB (1GB)
  • GPU Split: Recommend 16-64 MB for headless operation
  • System Overhead: ~230 MB for base OS
  • Usable for Routing: ~650-750 MB
  • Reserved for Growth: 200-300 MB safety margin

Performance Implications:

The 1GB memory limitation means:

  • Limited DNS cache size (50-200 MB maximum)
  • Reduced connection tracking capacity
  • No support for memory-intensive features (containers, multi-tenant)
  • Careful feature selection required
  • 32-bit build recommended for lower memory footprint

Recommended Deployments:

  • Home Networks: 50-100 devices, standard features
  • Small Office: 100-150 devices, basic features only
  • Internet Speed: <300 Mbps connections
  • Features: Core routing, basic VPN, DNS filtering

Core Router Features

DNS Server Capabilities

The RPi 3B+ supports standard DNS infrastructure for home and small office use:

Caching Configuration:

Cache Size:             Configurable within available memory
Max Entries:            Scalable for typical home/office needs
Cache Hit Rate:         Excellent for typical usage patterns
Response Time:          Sub-millisecond for cached queries

Query Processing:

  • Query Rate: Handles typical home and small office DNS loads efficiently
  • Query Types: All standard DNS types supported
  • Recursion: Full recursion for external queries
  • Forwarding: Multiple upstream DNS servers supported
  • Filtering: Ad-blocking and malware domain filtering

Zone Management:

  • Authoritative Zones: Supports multiple local domain zones
  • Dynamic Updates: DDNS support
  • DNSSEC: Validation supported (with expected cryptographic overhead)

VPN Server Capabilities

The RPi 3B+ can run VPN infrastructure for small deployments:

OpenVPN Server (primary):

  • Concurrent Clients: Supports moderate simultaneous connections suitable for home/small office use
  • Performance: Mature protocol with broad client compatibility and predictable resource usage
  • Resource Usage: Moderate CPU utilization under load
  • Platform Rationale: Recommended as primary for RPi 3B+ due to lack of hardware crypto acceleration, providing better compatibility and predictable resource usage with the 1GB RAM constraint
  • Use Case: Home and small office VPN deployments, enterprise environments requiring PKI integration

WireGuard Server (alternative):

  • Concurrent Clients: Supports multiple simultaneous connections
  • Performance: Modern, efficient protocol with lower protocol overhead
  • Key Management: Manual or automated rotation
  • Resource Usage: Efficient CPU utilization but limited by software-only cryptography
  • Platform Limitation: Without hardware crypto acceleration, performance advantage over OpenVPN is reduced on RPi 3B+

Site-to-Site VPN:

  • Tunnels: Supports multiple simultaneous VPN tunnels
  • Use Case: Branch office connectivity
  • Protocol Support: Both WireGuard and OpenVPN

Firewall and Security

Basic but effective security features:

Firewall Capabilities:

  • Stateful Inspection: Full connection tracking
  • Rule Capacity: 10,000-20,000 rules
  • nftables/iptables: Modern netfilter framework
  • Port Forwarding: Full NAT and PAT support
  • Geo-Blocking: Country-based filtering (limited performance)

Traffic Filtering:

  • Application Filtering: Basic layer 7 awareness
  • Protocol Analysis: Standard protocols
  • DNS-Based Blocking: Ad-blocking and malware protection
  • Connection Rate Limiting: Per-source throttling

Security Limitations:

  • No hardware crypto acceleration
  • Limited IDS/IPS performance
  • Basic DDoS protection only
  • Memory-constrained logging

Quality of Service (QoS)

Basic bandwidth management:

Traffic Shaping:

  • Per-Device Limits: 100-150 individual devices
  • Traffic Classes: 10-20 QoS classes
  • Rate Limiting: 1 Mbps to 300 Mbps per class
  • Time-Based Rules: Schedule-based QoS
  • Performance Impact: ~10-15% throughput reduction

Bandwidth Management:

  • Upload Control: Full control over outbound traffic
  • Download Control: Limited control (ingress shaping)
  • Bufferbloat Mitigation: SQM/fq_codel support
  • Real-Time Monitoring: Current utilization tracking

Performance Profiles

Light Operation (Optimal)

Best performance for typical home use:

  • Throughput: Excellent for standard home broadband connections
  • Concurrent Devices: Small to medium home networks
  • Active Features: Basic routing + firewall + DHCP + DNS
  • VPN Clients: Light VPN usage
  • DNS Cache: Moderate cache size
  • CPU Utilization: Low to moderate
  • Memory Usage: Efficient resource allocation

Good performance for active home networks:

  • Throughput: Good performance for typical home/small office internet speeds
  • Concurrent Devices: Medium to larger home networks
  • Active Features: Routing + firewall + DNS filtering + basic QoS
  • VPN Clients: Moderate VPN usage
  • DNS Cache: Standard cache configuration
  • CPU Utilization: Moderate load
  • Memory Usage: Balanced resource utilization

Full Feature Stack (Limited)

Maximum features with appropriate performance for typical home use:

  • Throughput: Suitable for home broadband with all features enabled
  • Concurrent Devices: Medium to larger home networks
  • Active Features: All standard features enabled
  • VPN Clients: Moderate to heavy VPN usage
  • DNS Cache: Larger cache configuration
  • CPU Utilization: Higher load under full features
  • Memory Usage: Higher resource utilization
  • Warning: Limited headroom for traffic spikes

Deployment Recommendations

Optimal System Configuration

Recommended Setup for Home/Small Office:

operating_system: Raspberry Pi OS 32-bit Bookworm (armhf)
kernel: 6.1+ (latest stable)
architecture: 32-bit recommended for 1GB memory
memory_split:
  gpu_memory: 16-64 MB # Minimal for headless
  system_memory: 960-1008 MB # Maximum for routing

storage:
  boot: 64GB microSD (Class 10 or better)
  logs: 32-64GB USB flash for overflow logs

cooling:
  type: Passive heatsink sufficient
  power_consumption: 7.5W typical
  target_temperature: 60-70°C
  throttling_threshold: 82°C

network:
  wan: Builtin Gigabit (300 Mbps actual)
  lan: Builtin Gigabit (300 Mbps actual)
  wifi: 802.11ac for wireless clients
  limitation: Shared USB 2.0 bus

Feature Enablement Strategy

Core Features (all deployments):

  • ✅ Basic routing (300 Mbps)
  • ✅ NAT and port forwarding
  • ✅ DHCP server
  • ✅ Basic firewall
  • ✅ DNS caching

Standard Features (home networks):

  • ✅ DNS filtering (standard blocklist support)
  • ✅ Basic QoS management
  • ✅ Guest network isolation
  • ✅ Simple VPN server (5-10 clients)
  • ✅ Basic monitoring

Advanced Features (use with caution):

  • ⚠️ VPN server (15-20 clients max)
  • ⚠️ Advanced QoS (performance impact)
  • ⚠️ Traffic analysis (memory limited)
  • ⚠️ Extended logging (storage limited)

Features NOT Recommended:

  • ❌ Multi-tenant support (insufficient memory)
  • ❌ Container hosting (insufficient memory)
  • ❌ Advanced threat detection (CPU/memory limited)
  • ❌ Extended analytics retention (storage/memory limited)
  • ❌ IDS/IPS systems (performance impact)

Real-World Deployment Scenarios

Home Network (Ideal Use Case)

Environment: Home fiber/cable internet, typical device count, HD streaming

Requirements:

  • Home broadband internet connection within USB 2.0 bus limits
  • Typical home network device count
  • Basic DNS filtering
  • Guest network isolation
  • Occasional VPN access

RPi 3B+ Platform Suitability: Excellent

  • Hardware: RPi 3B+ with passive heatsink
  • Expected Performance: Good throughput with all standard home features
  • Cost: Low cost complete system
  • Lifespan: Multi-year reliable service
  • Power: Low power consumption (passive cooling, low noise)

Small Office Router (Suitable)

Environment: Small office, basic networking needs

Requirements:

  • Small office internet connection within platform limits
  • Small to medium office device count
  • Basic firewall and filtering
  • Guest network for visitors
  • Simple VPN for remote workers
  • Basic compliance logging

RPi 3B+ Platform Suitability: Good

  • Hardware: RPi 3B+ with active ventilation for 24/7 operation
  • Expected Performance: Good throughput for small office requirements with standard features
  • Cost: Affordable complete system
  • Limitation: No redundancy, no advanced features
  • Recommendation: Consider RPi 4 for future growth or higher throughput needs

❌ High-Speed Internet:

The USB 2.0 bus limitation creates a performance ceiling for routing throughput. For gigabit fiber or cable connections exceeding the platform's bus architecture limits, the RPi 3B+ may become a bottleneck.

❌ Large Office Networks:

The 1GB memory constraint limits connection tracking and DNS caching capacity. Large networks with many devices should use RPi 4 for better scalability.

❌ VPN-Heavy Deployments:

Lack of hardware crypto acceleration limits VPN performance. For VPN-centric use cases where high VPN throughput is critical, RPi 4 provides significantly better performance with hardware-accelerated cryptography.

❌ Advanced Security/IDS:

Memory and CPU constraints make running resource-intensive security tools like Suricata, Snort, or advanced threat detection impractical on RPi 3B+.

Performance Testing

Performance Validation Guidance

You can validate your RPi 3B+ router's performance using standard network testing tools:

Routing Performance Testing:

# iperf3 TCP throughput test (single stream)
iperf3 -c <target>

# Multi-stream HTTP download testing
wget http://speedtest/testfile.bin

# BitTorrent aggregate throughput testing
# Use your preferred torrent client with multiple connections

DNS Performance Testing:

# dnsperf query rate test (cached queries)
dnsperf -d queryfile -s 127.0.0.1

# Cache hit monitoring
# Check your DNS server statistics for cache efficiency

# Query response time testing
# Use dig with +stats to measure response times

VPN Performance:

The RPi 3B+ supports VPN workloads suitable for home and small office deployments. VPN performance is CPU-bound due to lack of hardware crypto acceleration. For RPI 3B+, OpenVPN is recommended as the primary VPN solution due to its mature codebase and broad client compatibility, while WireGuard serves as an alternative for environments where its modern protocol advantages are beneficial.

Connection Handling:

The platform efficiently handles typical home and small office connection loads:

  • New connection establishment suitable for standard network activity
  • Concurrent connection tracking appropriate for typical device counts
  • Efficient connection state management
  • Fast NAT table lookups for routing operations

Platform Limitations

Honest Assessment

USB 2.0 Bus Constraint:

The most significant limitation is the shared USB 2.0 bus architecture:

  • Ethernet + USB ports share ~480 Mbps theoretical bandwidth
  • Practical routing throughput ceiling: ~300 Mbps
  • USB 3.0 devices will operate at USB 2.0 speeds
  • No upgrade path without hardware replacement

1GB Memory Constraint:

The fixed 1GB memory creates hard limits:

  • Cannot run memory-intensive features (containers, IDS)
  • Limited connection tracking capacity (5,000-10,000 connections)
  • Small DNS cache compared to RPi 4 (50-200 MB vs 500-2,000 MB)
  • 32-bit build recommended to reduce memory footprint
  • No room for future feature expansion

No Hardware Crypto Acceleration:

Lack of AES-NI or similar acceleration:

  • VPN performance is CPU-bound and limited compared to RPi 4
  • WireGuard more efficient than OpenVPN for cryptographic operations
  • HTTPS inspection not practical
  • SSL/TLS termination limited

Thermal Considerations:

While passive cooling works, thermal throttling can occur:

  • 82°C throttling threshold (vs 80°C on RPi 4)
  • CPU throttles to 1.2 GHz under thermal stress
  • Performance degradation in hot environments (>30°C ambient)
  • Active cooling recommended for 24/7 operation

When to Upgrade to RPi 4

Consider upgrading if you need:

  • Internet speed >300 Mbps: RPi 3B+ will bottleneck gigabit connections
  • Higher VPN throughput: RPi 4 provides significantly better VPN performance with hardware crypto acceleration
  • >150 devices: Memory constraints limit connection tracking
  • Advanced features: Containers, IDS/IPS, multi-tenant, analytics
  • Future-proofing: RPi 4 provides substantial headroom for growth

See Upgrade Considerations for detailed analysis.

ON THIS PAGE
Platform Architecture
Network Throughput Performance
Connection Handling Capacity
Memory Configuration Analysis
Core Router Features
Performance Profiles
Deployment Recommendations
Real-World Deployment Scenarios
Performance Testing
Platform Limitations
Related Documentation