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I recently purchased 2.5GB adapters for my main Desktop (Windows 10) and NAS server (Ubuntu 20.04).

When testing with iPerf3 FROM Windows, I only get 1GB. But when I use the --reverse flag, I get the 2.5GB (or close enough).

This occurs whether the -s server flag is on the Ubuntu or the Windows machine. I've also tried two different Ethernet cables, with the same results.

Server on Ubuntu.
Data FROM Windows TO Ubuntu:

H:\Downloads\iperf-3.1.3-win64
λ iperf3 -c 10.0.51.3
Connecting to host 10.0.51.3, port 5201
[  4] local 10.0.51.2 port 1111 connected to 10.0.51.3 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec   120 MBytes  1.01 Gbits/sec
[  4]   1.00-2.00   sec   120 MBytes  1.01 Gbits/sec
[  4]   2.00-3.00   sec   120 MBytes  1.00 Gbits/sec
[  4]   3.00-4.00   sec   118 MBytes   994 Mbits/sec
[  4]   4.00-5.00   sec   119 MBytes   994 Mbits/sec
[  4]   5.00-6.00   sec   120 MBytes  1.00 Gbits/sec
[  4]   6.00-7.00   sec   118 MBytes   992 Mbits/sec
[  4]   7.00-8.00   sec   117 MBytes   984 Mbits/sec
[  4]   8.00-9.00   sec   119 MBytes   999 Mbits/sec
[  4]   9.00-10.00  sec   117 MBytes   984 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-10.00  sec  1.16 GBytes   997 Mbits/sec                  sender
[  4]   0.00-10.00  sec  1.16 GBytes   997 Mbits/sec                  receiver

iperf Done.

Reverse - Data FROM Ubuntu TO Windows:

H:\Downloads\iperf-3.1.3-win64
λ iperf3 -c 10.0.51.3 --reverse
Connecting to host 10.0.51.3, port 5201
Reverse mode, remote host 10.0.51.3 is sending
[  4] local 10.0.51.2 port 1122 connected to 10.0.51.3 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec   273 MBytes  2.29 Gbits/sec
[  4]   1.00-2.00   sec   272 MBytes  2.28 Gbits/sec
[  4]   2.00-3.00   sec   276 MBytes  2.31 Gbits/sec
[  4]   3.00-4.00   sec   273 MBytes  2.29 Gbits/sec
[  4]   4.00-5.00   sec   274 MBytes  2.30 Gbits/sec
[  4]   5.00-6.00   sec   272 MBytes  2.29 Gbits/sec
[  4]   6.00-7.00   sec   275 MBytes  2.30 Gbits/sec
[  4]   7.00-8.00   sec   274 MBytes  2.30 Gbits/sec
[  4]   8.00-9.00   sec   276 MBytes  2.32 Gbits/sec
[  4]   9.00-10.00  sec   275 MBytes  2.30 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-10.00  sec  2.68 GBytes  2.30 Gbits/sec    0             sender
[  4]   0.00-10.00  sec  2.68 GBytes  2.30 Gbits/sec                  receiver

iperf Done.
EngageBasic
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  • I recently started having the exact same problem, only I'm using macOS and going to Debian. Only get 1Gb/s connection from macOS with the `-R` flag. I assumed it was some setting in macOS that changed, but guess not if it's also happening on Windows...? What's more strange is I'm pretty certain I tested both my 2.5Gb adapters previously and was getting the whole 2.5Gb in both directions. But it seemed to change and didn't correspond to any changes on mac or other hardware that I remember. – cpit May 02 '23 at 10:39

0 Answers0