• Thursday, August 21, 2025

UniFi Dual WAN Setup: Step-by-Step Guide for Load Balancing & Failover

 

Introduction: Understanding UniFi Dual WAN for Network Resilience

Network downtime costs businesses an average of $5,600 per minute, making redundant internet connections a critical investment for operational continuity. Multi-WAN networking involves using multiple internet connections simultaneously to eliminate single points of failure and optimize network performance. WAN redundancy can boost network availability by up to 85%, providing essential protection against service provider outages, equipment failures, and bandwidth constraints.

Understanding the three primary multi-WAN strategies is crucial for effective implementation:

  • Failover maintains one active connection while keeping backup connections on standby. When the primary WAN fails, traffic automatically switches to the secondary connection, ensuring continuity but not utilizing backup bandwidth during normal operations.
  • Load Balancing distributes traffic across multiple active connections simultaneously, maximizing available bandwidth and providing automatic failover. This approach optimizes performance by utilizing all connections but requires careful configuration to prevent session disruptions.
  • Bonding combines multiple connections into a single logical interface, aggregating bandwidth and providing redundancy. However, UniFi gateways support up to eight WAN interfaces with failover and load balancing capabilities, but lack native WAN bonding functionality.

UniFi's implementation focuses on per-session load balancing rather than true bonding, meaning individual connections remain on single WANs while new sessions distribute across available interfaces. This approach works well for most business scenarios but may not provide the seamless bandwidth aggregation some users expect. Understanding these limitations helps set realistic expectations and guides proper configuration strategies for optimal network resilience.

From Experience

In our experience working with small and midsize businesses, implementing UniFi Dual WAN setups has proven invaluable for reducing costly downtime during ISP outages. We've tested both failover and load balancing strategies in real-world deployments, and clients often find that policy-based routing provides a balanced approach for managing costs and performance. Real-world results show that proactive SLA monitoring and ongoing maintenance can prevent most common configuration issues before they impact users. By tailoring multi-WAN strategies to specific business needs, we've helped organizations maintain resilient, high-availability networks—even in areas with inconsistent broadband service.

Dual WAN Setup: Physical Configuration and Port Assignment

Setting up dual WAN on UniFi gateways begins with understanding your hardware capabilities. The UXG-Pro supports up to eight WAN interfaces, while the UDM Pro/SE can utilize any of its ports for WAN connections, including the dedicated WAN port plus configurable LAN ports. The UXG-Max features five 2.5 Gbps ports with dual-WAN capability.

Physical Connection Steps:

  1. Connect your primary ISP to the default WAN port (Port 1 on most models)
  2. Connect your secondary ISP to a designated LAN port that you'll reconfigure as WAN2
  3. Ensure both connections are active and receiving IP addresses from their respective ISPs

UniFi Network Application Configuration:

  1. Navigate to UniFi Devices in your Network application
  2. Select your gateway device to open the device panel
  3. Click Ports tab to access port configuration
  4. Select the LAN port you want to convert to WAN2
  5. Change the port profile from LAN to WAN
  6. Configure the network settings (DHCP, Static IP, or PPPoE based on your ISP requirements)
  7. Apply changes and wait for the connection to establish

Initial Network Settings:

For each WAN interface, configure the appropriate connection type. Most residential connections use DHCP, but business connections may require static IP configuration. UniFi supports up to eight WAN interfaces total, limited only by available physical ports while reserving at least one for LAN connectivity.

Verify both WAN connections show as "Connected" in the Network application before proceeding to load balancing or failover configuration.

Failover vs Load Balancing: Choosing Your WAN Strategy

When designing your Dual WAN strategy, choosing between failover and load balancing depends on your connection types, budget, and business requirements. Each approach serves distinct purposes and configuration scenarios.

Failover: Your Safety Net Strategy

Failover mode keeps your primary WAN active while the secondary remains standby, only engaging when the primary connection fails. This strategy works best when:

  • Your secondary connection is expensive or metered (like LTE)
  • You have significantly different connection speeds (fiber primary, DSL backup)
  • Cost control is critical for your business budget

Configure failover by setting your primary WAN as the default route and enabling SLA monitoring to detect outages quickly.

Load Balancing: Maximizing Your Investment

Load balancing distributes traffic across multiple active connections simultaneously. UniFi supports up to eight WAN interfaces in load balancing mode, making it ideal when:

  • Both connections have unlimited data plans
  • Similar connection speeds and reliability
  • You need maximum bandwidth utilization
  • Business operations require consistent high throughput

Real-World Decision Framework

  • Choose Failover if:
    • Secondary WAN has data caps or high costs
    • Connections have vastly different speeds
    • Minimal complexity is preferred
  • Choose Load Balancing if:
    • Both connections are unlimited and reliable
    • You need maximum bandwidth aggregation
    • Traffic distribution improves performance

Pro Tip: Consider policy-based routing for hybrid approaches—route critical traffic through your premium connection while using the secondary for general browsing or guest networks. This gives you both cost control and performance optimization without choosing a single strategy.

Advanced Configuration: SLA Monitoring and Policy-Based Routing

SLA Monitoring Configuration

Service Level Agreements (SLAs) provide precise WAN health monitoring by continuously testing connection quality through ping and DNS requests. Navigate to Settings > Internet in your UniFi Network console, then select your WAN interface to configure SLA monitoring.

Configure ping targets using reliable servers like 8.8.8.8 or 1.1.1.1, setting latency thresholds between 50-100ms and packet loss limits at 5-10% based on your network requirements. UniFi's SLA monitoring supports both ping and DNS-based health checks to ensure accurate failover detection, preventing false positives from temporary network hiccups.

Set monitoring intervals to 30-60 seconds for responsive failover without overwhelming your connection. Enable jitter monitoring for VoIP or real-time applications that require consistent latency performance.

Policy-Based Routing Setup

Policy-Based Routing directs specific traffic through designated WAN connections, optimizing bandwidth usage and controlling costs. Access Routing > Policy Routes in your UniFi console to create traffic rules based on source devices, destinations, or applications.

Configure device-specific routing by creating policies that match client MAC addresses or IP ranges. For example, route streaming devices through your unlimited connection while directing IoT devices through a secondary link. UniFi's Policy-Based Routing supports destination-based rules, allowing you to route cloud services or specific websites through particular WAN connections.

Create application-specific policies using port numbers or protocol types. Route VoIP traffic (ports 5060-5061) through your primary low-latency connection while sending backup traffic through secondary links during off-peak hours. This granular control prevents unexpected overage charges on metered connections while maintaining optimal performance for critical applications.

Troubleshooting and Best Practices for UniFi Multi-WAN Networks

When your UniFi multi-WAN setup isn't performing as expected, systematic troubleshooting can quickly identify and resolve common issues.

Common Configuration Problems

The most frequent issue is improper SLA (Service Level Agreement) settings. Default ping intervals may be too aggressive for some connections, causing false positives. Configure SLA monitoring with 5-second intervals and 3-packet loss tolerance for stable failover detection.

Static IP configurations often cause failover failures. Ensure both WAN connections have proper gateway settings and DNS servers configured. Test connectivity using the UniFi console's built-in ping tools to verify each WAN path independently.

Diagnostic Steps

  1. Check WAN Status: Navigate to Network → Internet and verify both connections show "Connected" status
  2. Test SLA Response: Monitor the SLA graphs for consistent ping responses and packet loss patterns
  3. Verify Routing Tables: Use SSH access to check routing priorities with ip route show
  4. Review Logs: Examine system logs for WAN transition events and error messages

Best Practices for Monitoring

Implement proactive monitoring by setting SLA targets to reliable external hosts (8.8.8.8, 1.1.1.1) rather than ISP gateways. Configure failover sensitivity to avoid unnecessary switching during minor ISP hiccups.

For metered connections, create traffic policies that route high-bandwidth applications (streaming, backups) exclusively through unlimited connections. Set bandwidth limits on metered WANs to prevent overage charges.

Optimal failover response times typically range from 30-90 seconds. Faster switching may cause connection instability, while slower responses impact user experience. Monitor failover events regularly and adjust SLA thresholds based on your network's specific requirements and ISP reliability patterns.

Sources

Written by Alex Barreras, an IT solutions expert and the founder of Barreras IT Corp, a Miami-based managed service provider. With extensive experience in networking, cybersecurity, cloud hosting, and ERP systems like Odoo, he helps businesses streamline operations and strengthen their digital infrastructure. Alex specializes in delivering tailored IT support, web hosting, and automation solutions that balance performance, security, and cost efficiency.

 

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