Posted: Tue Oct 24, 2023 20:12 Post subject: On R7000P ethernet suddenly slowing down
I have R7000P running DD-WRT v3.0-r53544 and two PCs running Windows 11 connected to it using Realtek 2.5G Ethernet adapters.
Suddenly on the one of the PCs speed drops from Gb/s to Kb/s when copying files in Windows. It is still possible to copy files from another PC to that PC with the full Gb/s speed, so the speed loss is asymmetric.
Restarting Ethernet with the Restart-NetAdapter -Name "Ethernet" PowerShell command helps to restore speed.
What this could be and how I can perform some diagnostics?
I would guess the Realtek network drivers in Windows are the problem. If you were to swap the ssds in your 2 windows machines and load Linux on both of them very likely copying over SMB between Linux boxes would work fine. If you look at the Linux source code for Realtek drivers there are all kinds of programmers comments about various hardware bugs in the chips.
The Intel network chips are used in most of the performance tests that are published online for this reason. Intel worked closely with the OSS community when they developed their networking chips and learned a lot about how to properly design adapter silicon.
Realtek has released multiple Windows drivers for their chips. It's harder nowadays with windows 11 to try them out but still possible.
What I have found so far is that speed drops to 4-6 MBps s instead of KBps when "Large send offload" both for IPv4 and IPv6 is disabled in driver settings. Disabling all power saving settings does not help.
Joined: 01 Dec 2021 Posts: 289 Location: Maryland, United States
Posted: Sat Nov 11, 2023 17:35 Post subject:
I also have the R7000P router. Realtek has two types of drivers. One of them is without power savings. See if that helps. I have not transferred files between computers, but I got reduced performance with the power saving driver.
Also Mbps is faster than KBps do you have a typo in your post by any chance?
Strangely, these mysterious speed drops end in better performance when Large Send Offload is disabled on NIC. But they still happen. I didn't change DD-WRT offload settings.
I tried energy saving drivers, but found no difference. As I understand, with these drivers energy saving is simply disabled by default in the advanced NIC settings. Performance still drops mysteriously.
Today I rebooted the router and found the same slowdown from the moment of boot on all my machines.
I suppose either I have faulty hardware, or there is a systematic problem in dd-wrt, that was missed because of some unusual conditions. The slowdowns happen with a considerable uptime, and all my machines have generally large one (either constantly on or use hibernation). Also the internet speed is OK, only the intranet ethernet speed becomes low. I also had sometimes the same problem on my previous Netgear WNDR4300, but much more rarer.
It turns out that this is an issue with cables. Somehow shielding the cable with aluminum foil in the places where it contact other cables helps to get a stable connection. Will replace my UTP cat 5e with 6.