USG FLEX H Series - Network Trunk Enhancements

Zyxel_Richard Posts: 249  Zyxel Employee
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edited May 17 in Networking

USG FLEX H Series - Network Trunk Enhancements

In firmware version 1.20, several enhancements have been made to the network trunk options for the USG FLEX H Series. These enhancements include new WAN load balancing algorithms and improved load balancing criteria, offering more flexibility and control over network traffic management. This article will cover the new features and explain how to configure and utilize them effectively.

WAN Load Balancing Algorithms

Default Algorithm: Weighted Round Robin (WRR)

The default algorithm, Weighted Round Robin, distributes traffic equally across multiple WAN interfaces in a round-robin fashion. Each session is alternately assigned to the WAN interfaces in sequence, ensuring a balanced distribution.

New Algorithms - Spillover:

  • Primarily uses the main WAN interface until a specified traffic threshold is reached.
  • After reaching the threshold, additional traffic "spills over" to the secondary WAN interface.
  • Ideal for scenarios where the primary WAN interface has unlimited bandwidth and the secondary interface is metered.

New Algorithms - Least Load First:

  • Directs traffic to the WAN interface with the least current load.
  • Balances traffic based on utilization(percentage), ensuring efficient usage of available bandwidth.
  • Useful for maximizing the performance of multiple WAN connections with varying bandwidths.

Load Balancing Index

The load balancing index determines the criteria for measuring bandwidth load usage. It offers three options:

  • Inbound: Measures incoming traffic.
  • Outbound: Measures outgoing traffic.
  • Sum: Measures the total of both inbound and outbound traffic.

Configuring WAN Load Balancing

  • Navigate to Network Interface:
    • Go to the Network section in your firewall’s configuration interface.
    • Select Interface and then Trunk.
  • Create User Defined Trunk:
    • Click on the Add button to create a new trunk.
    • Choose the load balancing algorithm (e.g., Spillover or Least Load First).
  • Set Load Balancing Index:
    • Select the appropriate load balancing index (Inbound, Outbound, or Sum).
  • Add Interfaces:
    • Add the WAN interfaces you want to include in the trunk.
    • Specify the bandwidth limits for each interface.

Practical Scenarios for WAN Load Balancing

Spillover Scenario
  • Primary WAN (WAN1): Unlimited bandwidth, preferred for regular traffic.
  • Secondary WAN (WAN2): Metered connection, used only when primary exceeds 800 Mbps.
  • Outcome: Regular traffic utilizes WAN1, and only excess traffic spills over to WAN2, saving costs on metered usage.
Least Load First Scenario
  • Multiple WAN Connections: Different bandwidth capacities.
  • Outcome: Traffic is dynamically routed to the interface with the least load, optimizing the usage of available bandwidth and improving overall network performance.

Applying User Defined Trunk

Set Default Trunk Routing:
  • After creating a user-defined trunk, go to the Network section and select Interface.
  • Click on Default Trunk and choose the user-defined trunk profile to set it as the default WAN load balancing policy.


The new WAN load balancing algorithms and load balancing index options in the USG FLEX H Series firmware version 1.20 provide enhanced flexibility and efficiency for managing network traffic. By understanding and utilizing these features, administrators can optimize their network performance and ensure efficient use of bandwidth across multiple WAN connections.