Assymetrical Speeds Using Iperf

Hey everyone,

I’ve had a TrueNas system for quite some time now, and I’m still trying to figure out why I am not getting the gigabit speeds I should be getting. My PC is in the basement and directly wired into the network switch that provides my whole home ethernet. The ethernet in my home is Cat 5e (I know it’s old but should still be able to handle near gigabit speeds).

I have done the following:

  • Replaced ethernet cable
  • Reinstalled TrueNas
  • Swapped out old disks

I use Iperf3 on windows and on the TrueNas and this is the interesting result I get.

When I run iperf -c TrueNasAddress I get:

When I run iperf -R -c 192.168.1.125 I get:

I’m confused as to why from the client (Windows 10 PC) → (TrueNas Core NAS) I get significantly slower speeds than when it is (TrueNas Core NAS) → (Windows 10 PC).

If anyone could give me any insight on what to do in order to try to fix/diagnose this issue?

Sorry the post didn’t let me upload pictures for some reason (definitely me just being dumb)

Command: iperf3.exe -c 192.168.1.125
Connecting to host 192.168.1.125, port 5201
[ 5] local 192.168.1.67 port 51980 connected to 192.168.1.125 port 5201
[ ID] Interval Transfer Bitrate
[ 5] 0.00-1.01 sec 14.8 MBytes 123 Mbits/sec
[ 5] 1.01-2.00 sec 16.5 MBytes 140 Mbits/sec
[ 5] 2.00-3.01 sec 12.9 MBytes 107 Mbits/sec
[ 5] 3.01-4.00 sec 11.4 MBytes 96.2 Mbits/sec
[ 5] 4.00-5.01 sec 12.5 MBytes 104 Mbits/sec
[ 5] 5.01-6.01 sec 11.6 MBytes 97.0 Mbits/sec
[ 5] 6.01-7.00 sec 11.0 MBytes 93.2 Mbits/sec
[ 5] 7.00-8.01 sec 11.2 MBytes 94.0 Mbits/sec
[ 5] 8.01-9.01 sec 10.0 MBytes 83.4 Mbits/sec
[ 5] 9.01-10.01 sec 10.8 MBytes 91.0 Mbits/sec


[ ID] Interval Transfer Bitrate
[ 5] 0.00-10.01 sec 123 MBytes 103 Mbits/sec sender
[ 5] 0.00-10.01 sec 122 MBytes 103 Mbits/sec receiver

iperf Done.

Command iperf3.exe -R -c 192.168.1.125
Connecting to host 192.168.1.125, port 5201
Reverse mode, remote host 192.168.1.125 is sending
[ 5] local 192.168.1.67 port 56856 connected to 192.168.1.125 port 5201
[ ID] Interval Transfer Bitrate
[ 5] 0.00-1.00 sec 108 MBytes 900 Mbits/sec
[ 5] 1.00-2.01 sec 109 MBytes 908 Mbits/sec
[ 5] 2.01-3.00 sec 109 MBytes 924 Mbits/sec
[ 5] 3.00-4.01 sec 111 MBytes 924 Mbits/sec
[ 5] 4.01-5.00 sec 110 MBytes 926 Mbits/sec
[ 5] 5.00-6.01 sec 111 MBytes 925 Mbits/sec
[ 5] 6.01-7.00 sec 110 MBytes 926 Mbits/sec
[ 5] 7.00-8.01 sec 111 MBytes 926 Mbits/sec
[ 5] 8.01-9.00 sec 110 MBytes 927 Mbits/sec
[ 5] 9.00-10.01 sec 111 MBytes 926 Mbits/sec


[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.01 sec 1.08 GBytes 923 Mbits/sec 21 sender
[ 5] 0.00-10.01 sec 1.07 GBytes 921 Mbits/sec receiver

iperf Done.

You are just having all sorts of trouble posting. No pictures and then the same test twice. :rofl:

LOL WOW that’s embarrassing

update: uploaded the screenshots


Are you using more than a single network port/NIC on your NAS or your Windows PC?

No. I have one port on my PC it’s a 2.5gb port on a gigabyte aurous b550i. I then have one port on my NAS motherboard which is a Asus prime b450m-a/csm.