Slow speed between client and RT-AX82U using iperf3

[lucy37]

Hi, I am trying to find the maximum bandwidth in my local network so I SSHed into my Asus RT-AX82U and launched an iperf3 server.
I then used my Ubuntu (WSL) to speed test it but I am getting low speeds:

iperf3 -c router.asus.com -P 8 -t 1000 -R
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[  5]   0.00-78.57  sec   804 MBytes  85.8 Mbits/sec                  receiver
[  7]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[  7]   0.00-78.57  sec  1.25 GBytes   136 Mbits/sec                  receiver
[  9]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[  9]   0.00-78.57  sec   731 MBytes  78.0 Mbits/sec                  receiver
[ 11]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[ 11]   0.00-78.57  sec   823 MBytes  87.9 Mbits/sec                  receiver
[ 13]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[ 13]   0.00-78.57  sec   811 MBytes  86.5 Mbits/sec                  receiver
[ 15]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[ 15]   0.00-78.57  sec   553 MBytes  59.1 Mbits/sec                  receiver
[ 17]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[ 17]   0.00-78.57  sec   536 MBytes  57.2 Mbits/sec                  receiver
[ 19]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[ 19]   0.00-78.57  sec   633 MBytes  67.6 Mbits/sec                  receiver
[SUM]   0.00-78.57  sec  0.00 Bytes  0.00 bits/sec                  sender
[SUM]   0.00-78.57  sec  6.02 GBytes   658 Mbits/sec                  receiver
iperf3: interrupt - the client has terminated

The crazy part is that when running speedtest, either from one my computers or from the router itself, I am getting around 1000Mbits/s without any problems, so I must be doing something wrong here.

My computer is connected through 5GHz at around -56 dBm

 

[ColinTaylor]

Running iperf on the router is not a representative test. It would be better to test iperf between two devices on the LAN, with at least one of them connected by Ethernet.

 

[lucy37]

Running iperf on the router is not a representative test. It would be better to test iperf between two devices on the LAN, with at least one of them connected by Ethernet.

Why is that? Also how come speedtest gives higher results?

 

[ColinTaylor]

Why is that? Also how come speedtest gives higher results?

The traffic is taking different paths. LAN to LAN is switched and therefore should operate at wire speed (gigabit). WAN to LAN uses flow control to mostly offload the CPU to achieve greater than gigabit throughput. Router to WLAN has to process most of the traffic using the router's CPU which creates a potential bottleneck in performance. In other words the router isn't optimised to be the source or destination for large volumes of traffic and can therefore give unrepresentative results.

 

[lucy37]

The traffic is taking different paths. LAN to LAN is switched and therefore should operate at wire speed (gigabit). WAN to LAN uses flow control to mostly offload the CPU to achieve greater than gigabit throughput. Router to WLAN has to process most of the traffic using the router's CPU which creates a potential bottleneck in performance. In other words the router isn't optimised to be the source or destination for large volumes of traffic and can therefore give unrepresentative results.

It is even slower between two computers

C:\Users\Lucy\Downloads\iperf-2.0.9-win64>iperf.exe -c 192.168.50.46 -P 4 -t 10
------------------------------------------------------------
Client connecting to 192.168.50.46, TCP port 5001
TCP window size:  208 KByte (default)
------------------------------------------------------------
[  6] local 192.168.50.217 port 64986 connected with 192.168.50.46 port 5001
[  4] local 192.168.50.217 port 64984 connected with 192.168.50.46 port 5001
[  5] local 192.168.50.217 port 64985 connected with 192.168.50.46 port 5001
[  3] local 192.168.50.217 port 64983 connected with 192.168.50.46 port 5001
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  69.5 MBytes  58.2 Mbits/sec
[  5]  0.0-10.0 sec  69.2 MBytes  58.1 Mbits/sec
[  3]  0.0-10.0 sec  69.9 MBytes  58.5 Mbits/sec
[  6]  0.0-10.0 sec  70.0 MBytes  58.6 Mbits/sec
[SUM]  0.0-10.0 sec   279 MBytes   233 Mbits/sec

 

[ColinTaylor]

It is even slower between two computers

C:\Users\Lucy\Downloads\iperf-2.0.9-win64>iperf.exe -c 192.168.50.46 -P 4 -t 10
------------------------------------------------------------
Client connecting to 192.168.50.46, TCP port 5001
TCP window size:  208 KByte (default)
------------------------------------------------------------
[  6] local 192.168.50.217 port 64986 connected with 192.168.50.46 port 5001
[  4] local 192.168.50.217 port 64984 connected with 192.168.50.46 port 5001
[  5] local 192.168.50.217 port 64985 connected with 192.168.50.46 port 5001
[  3] local 192.168.50.217 port 64983 connected with 192.168.50.46 port 5001
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  69.5 MBytes  58.2 Mbits/sec
[  5]  0.0-10.0 sec  69.2 MBytes  58.1 Mbits/sec
[  3]  0.0-10.0 sec  69.9 MBytes  58.5 Mbits/sec
[  6]  0.0-10.0 sec  70.0 MBytes  58.6 Mbits/sec
[SUM]  0.0-10.0 sec   279 MBytes   233 Mbits/sec

Are both of these computers connected directly to the router by Ethernet?

 

[lucy37]

Are both of these computers connected directly to the router by Ethernet?

No, they are both using WiFi 6 over 5GHz

 

[ColinTaylor]

No, they are both using WiFi 6 over 5GHz

There are many variables that can effect throughput when using WiFi connections. That's why it's best to start by confirming you can get gigabit throughput using two Ethernet connected PCs.

 

[lucy37]

There are many variables that can effect throughput when using WiFi connections. That's why it's best to start by confirming you can get gigabit throughput using two Ethernet connected PCs.

Both computers get around 1000 Mbits\s when doing speed test, also the Asus interface reports both of them to have around 1200 Mbits\s (Tx\Rx rate)