uOS -Default Trunk Algorithm

Zyxel_Lynn

Overview

In the latest firmware release, Zyxel firewalls introduce an important change to the default WAN trunk configuration.
The default trunk algorithm has been updated to Least Load First, replacing the previous default of Weighted Round Robin.

This change improves load distribution efficiency and ensures consistent behavior with other ZLD firewall.

1.Default Trunk Algorithm Change

Firmware Version	Default Algorithm	Behavior
Previous Versions	Weighted Round Robin (WRR)	Sessions distributed evenly by count, regardless of link bandwidth.
Latest Version	Least Load First (LLF)	Sessions distributed based on real-time WAN utilization.

Reason for the Change

• Aligns trunk behavior across all Zyxel firewall product lines.
• Prevents Link Sticking from unintentionally locking sessions to slower WANs when using Weighted Round Robin.
• Ensures better performance in mixed-bandwidth environments (e.g., WAN1 = 100 Mbps, WAN2 = 1 Gbps).

In short, the new default setting makes WAN utilization smarter, fairer, and more efficient.

2.Configuration Behavior and Flexibility

Editable Default Trunk

In earlier firmware versions, the Default Trunk was fixed and could not be modified.
With this release, the Default Trunk Algorithm is now configurable.

Administrators can select any of the supported algorithms:

Algorithm	Description
Least Load First	Distributes sessions based on current WAN usage. Ideal for dynamic load balancing.
Weighted Round Robin	Distributes sessions by weight ratio. Suitable for equal-bandwidth WANs.
Spillover	Sends traffic through the primary WAN until its threshold is reached, then overflows to others.

How to Change the Default Trunk Algorithm

1. Go to Network > Interface > Trunk.
2. Select the Default WAN Trunk.
3. Click Edit and choose your preferred Algorithm from the dropdown list.
4. Click Apply to save changes.

⚠️ Note:
The parameter settings (e.g., bandwidth limit, weights) cannot be modified in the Default Trunk itself.
If customization is required, create a User-Defined Trunk.

3.Recommended Usage

Deployment Type	Recommended Algorithm	Notes
Mixed-speed WANs	Least Load First	Balances usage based on load; prevents session bias.
Equal-bandwidth WANs	Weighted Round Robin	Simple and predictable; good for symmetric links.
Priority-based backup link	Spillover	Ensures backup WAN is only used when primary link is full.

4.Summary

Aspect	Description
Feature	Default WAN Trunk Algorithm
Previous Default	Weighted Round Robin
New Default	Least Load First
Purpose	Align with other Zyxel models and improve bandwidth fairness
Configurable	Yes (can switch to WRR or Spillover)
Custom Parameters	Only available via User-Defined Trunk
Effect on Link Sticking	Prevents slow-link bias in multi-WAN environments

Key Takeaway

The Default Trunk Algorithm has been modernized to Least Load First, providing more intelligent and bandwidth-aware load balancing. This adjustment ensures smoother traffic distribution, better multi-WAN utilization, and alignment with other Zyxel firewall families.