When network vendors talk about bandwidth aggregation, the term often sounds magical multiple WAN connections pooled together to give you one fat pipe. But in reality, not all aggregation is created equal. Let’s peel back the layers and see what’s really happening.

Most edge routers that advertise bandwidth aggregation are actually using load balancing, typically a Weighted Round Robin (WRR) mechanism. Here’s how it works:

Multiple WAN connections (say two broadband links) are configured on the router.

The router distributes outgoing TCP connections across these links based on assigned weights. For example, if WAN1 is 100 Mbps and WAN2 is 50 Mbps, the router might assign a 2:1 ratio, sending twice as many sessions over WAN1 as WAN2.

During a speedtest or a file download manager with multiple threads, the application creates multiple TCP connections. Each of these connections is spread across the available WANs, making it appear that the total bandwidth is the sum of all links.