25GbE - Odd Window Problem - Limited Downloads
25GbE - Odd Window Problem - Limited Downloads
I'm still trying to understand this situation but thought it worth sharing. It appears to be a Windows-related problem, though I'm not entirely sure. The setup involves two 25GbE NICs connected to a switch that supports 25GbE. Data travels at 25GbE over the network, and uploads from Windows to remote servers also use this speed using tools like iperf2 and iperf3 (around 24Gb/s with iperf2, 21 with iperf3). However, downloads from the remote server to my Windows machine are problematic. Despite various adjustments—disabling security features, reinstalling drivers, changing NIC settings, and testing on different networks—I still get capped around 12.5Gb/s for downloads. I've also tried running two VMs on separate VLANs that communicate across the switch, achieving up to 24.5Gb/s in both directions without issues, which suggests the issue is specific to my own machine. No signal drops are visible on the switch, and everything seems normal, so I'm leaning toward a Windows-related bottleneck. I haven't tested safe mode with networking yet, but that's something I'll consider next. Anyone familiar with @mynameisjuan or @leadeater might have insights?
Restarted in Safe Mode with networking and suddenly achieved 24.5Gbit per direction, indicating a likely issue in Windows.
You're right about my limitations on the host OS. Safe Mode with Networking should activate the necessary drivers, so the issue likely lies elsewhere. I'm not familiar with specific signs in Task Manager or Resource Monitor, but I can help you investigate further if you share what you observe.
It seems unusual that performance is lower under normal conditions. Disabling Defender Real Time Protection might be the issue—network inspection can be turned off via GPO settings. In Safe Mode, the feature doesn't function properly, which points to this as the most probable cause. Also, verify the NIC hardware properties in Windows Drivers and ensure all offloads are enabled, along with adjusting buffer sizes. The driver defaults in Safe Mode are unlikely to be the problem. Increasing buffer or ring sizes typically improves results.