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I have a RPi3B connected via ethernet to a GbE Switch that also connects to my main PC. This PC gets 210/105 Mbps since it has a GbE port. I know that 3B only has a 10/100 ethernet port, but I'm getting very low donwload speeds, while the upload seems fine. I've run like 20 tests via speedtest-cli and the download speed ranges from 5 Mbps to 55Mbps (very very unstable measurements, mostly at ~15-25Mbps), while the upload always ranges from 93-94Mbps. Any idea why?

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    Hello and welcome -- Are you sure about the switch's configuration? Check QoS out. Connect raspberry pi directly to a host without any in-between devices and figure it out again.
    – M. Rostami
    Feb 1 '20 at 21:34
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You don't tell us where the other end of the up-/download is located. This has a significant impact. But you should verify that your local network is working properly. You can use iperf for it. I assume your PC has an Unix like operating system running so you can install it there. On a Debian derivative you will do it with:

pc ~$ sudo apt install iperf

Just do the same on the RasPi. Then on the PC start:

pc ~$ iperf --server

Assuming for example the PC has the ip address 192.168.50.174, then run on the RasPi:

rpi ~$ iperf --client 192.168.50.174
------------------------------------------------------------
Client connecting to 192.168.50.174, TCP port 5001
TCP window size:  114 KByte (default)
------------------------------------------------------------
[  3] local 192.168.50.137 port 58934 connected with 192.168.50.174 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   806 MBytes   855 Mbits/sec

On my GBit network I get 855 Mbits/sec. I'm satisfied.

This checks the upload speed. You can run iperf --server on the RasPi and use the PC as iperf --client. This will check the download speed.

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  • Hi, thanks for the quick tutorial. I had already tested via iperf. I made the tests again twice and the results were: 95.2 Mbits/sec and 95.1 Mbits/sec. It seems to be fine network wise.
    – Paulos
    Feb 3 '20 at 23:19
  • @Paulos OK, that means the RasPi is working properly. The problem is elsewhere, that can't be answered on Raspberry Pi ...
    – Ingo
    Feb 4 '20 at 0:34
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You will not observe maximum throughput unless files are large (20+ MB). When testing speed, I recommend using several 1GB+ files (videos).

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    speedtest-cli is a much more reliable way to test the connection speed than copying files. Feb 2 '20 at 19:27

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