Link Aggregation Issue: Download Speed Capped at 25 Mbps Resolved by Switching to Hetzner Cloud

[vinc32]

Summary

In issue #3225, I reported a problem where link aggregation wasn’t working as expected. After extensive testing, I finally identified the root cause. If you’re experiencing issues with download speeds while upload performance seems fine, this might be relevant to you.

Expected Behavior

Link aggregation should provide a combined capacity across all connections, ideally achieving speeds around 40-50 Mbps.

Issue

I tested various standard proxies, but only Shadowsocks worked, maxing out at 25 Mbps. Other proxies failed with errors like “Can’t get IP from xxx.” Despite the download limitations, upload performance remained strong.

Troubleshooting

I experimented with different proxies, overflow settings, and combinations of connections (one at a time, or two at once), but the download speed consistently maxed out at 25 Mbps. I even tried a new VPS at IONOS, but the issue persisted.

After months of troubleshooting, I decided to check the CPU and RAM usage on the server. Both were consistently reaching 100%, so I upgraded to a VPS with more cores and RAM, but there was no improvement. Notably, speed tests on the VPS itself showed 500 Mbps, indicating no inherent network issue.

Used Components

•	Ionos Cloud VPS: XS, S, M
•	Router: ESXi combined ext 4 EFI & hardware firewall with SquashFS image (various versions)
•	WAN: DSL (100 Mbps), Starlink, 5G

Solution

Switching to a Hetzner Cloud CX22 instance resolved the issue, achieving 55 Mbps with Kernel 6.6 and Shadowsocks Rust 2022 ;)