In the world of SD-WAN, businesses are moving beyond single-link dependencies and embracing bonding technology to improve performance, resilience, and reliability.
Bonding multiple internet links together allows organisations to combine bandwidth from different sources, creating a more stable and performant network connection.
However, bonding isn’t just about slapping multiple links together and expecting magic to happen. Not all link pairings are equal, and if one of your links is significantly weaker than the other, your aggregated bandwidth will not be as efficient as you might hope.
Let’s break it down!
How SD-WAN Bonding Works
SD-WAN bonding (also called link aggregation) takes multiple network links—be it fibre , LTE , wireless , or satellite —and combines them into a single logical connection. This allows traffic to be distributed across all available links in a way that maximises bandwidth and reduces packet loss.
Types of SD-WAN Bonding:
1. Packet-Level Bonding
- Splits packets across multiple links, ensuring full utilisation of available bandwidth.
- Requires careful packet reordering and jitter compensation.
2. Flow-Based Load Balancing
- Assigns different traffic flows (e.g., VoIP vs. file transfers) to different links based on performance.
- Less efficient than true bonding but simpler to implement.
3. Application-Aware Aggregation
- Uses Deep Packet Inspection (DPI) to intelligently route specific applications over the best-performing links.
- Can dynamically adjust based on link health and congestion levels.
The Limitations of Unequal Link Bonding
The dream scenario is to double or triple your bandwidth by bonding multiple links together. The reality? If one link is significantly slower than the others, it becomes a bottleneck that limits the overall benefit.
Why is this the case?
The 30% Rule: If one link is less than 30% of the bandwidth of the other, it struggles to contribute effectively in a bonded scenario.
- Example: If you bond a 200 Mbps fibre link with a 20 Mbps LTE link, the LTE connection barely adds value because packet distribution cannot be even.
- High-speed packets on the fibre link will arrive much faster than those on LTE, causing jitter and packet reordering issues.
Packet Fragmentation & Latency Issues
- SD-WAN bonding algorithms attempt to split packets evenly across all available links, but when one link is too slow, packets routed through it arrive late.
- This forces the SD-WAN appliance to reassemble out-of-sync packets, introducing delays.
- VoIP calls and real-time applications suffer the most!
Limited Aggregation Gains
- A 200 Mbps + 20 Mbps link pair does NOT equal 220 Mbps of usable bandwidth.
- Due to overheads and imbalance, you might only see 205 Mbps in real-world conditions.
Best Practices for Effective SD-WAN Bonding
To get the most out of link bonding, businesses should follow these best practices:
1. Use Links with Similar Capacities
Ideally, bonded links should be within 50-70% of each other’s capacity.
Example: A 100 Mbps link + a 70 Mbps link will bond efficiently.
But a 100 Mbps + 10 Mbps link? Not a good idea!
2. Ensure Links Have Similar Latency & Jitter Characteristics
Bonding a fibre link (5ms latency) with satellite (600ms latency) is a disaster waiting to happen.
Try to match links with similar response times to avoid packet reordering and buffer issues.
3. Configure Adaptive Bandwidth
Adaptive bandwidth in SD-WAN dynamically adjusts the amount of data sent over each link based on real-time network conditions such as latency, jitter, packet loss, and congestion.
Instead of rigidly splitting traffic, it intelligently allocates bandwidth to the best-performing links at any given moment, ensuring optimal speed, reliability, and quality for applications.
This prevents weaker links from becoming bottlenecks and improves overall network efficiency, especially in multi-link environments.
Use SD-WAN Solutions That Handle Asymmetric Bonding Smartly
✅ Not all SD-WANs are created equal!
✅ Some struggle with managing disparate links effectively.
✅ Fusion’s SD-WAN, for example, uses intelligent bonding that adapts to link conditions in real time, ensuring optimal performance.
Wrap | Balance is Key in SD-WAN Bonding
Bonding multiple links in SD-WAN is a powerful way to increase bandwidth, improve reliability, and enhance business continuity. However, not all links are created equal, and adding a significantly weaker link to a high-speed connection can negatively impact performance rather than enhance it.
By following best practices—matching link capacities, ensuring similar latencies, and using adaptive bonding techniques—businesses can fully unlock the benefits of SD-WAN without running into frustrating bottlenecks.
And remember, if your network team just throws links together without considering these factors, you might find your “bonded” setup performing worse than a single well-managed link. Don’t let that happen!
✅ Choose the right SD-WAN solution.
✅ Configure it properly.