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phippu
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Joined: Sun Jul 04, 2021 10:51 pm

TCP Retries If Data Flows Over CPU

Sun Jul 04, 2021 11:03 pm

Hello everyone!

I am pretty new to RouterOS and Mikrotik in general. I have a new internet connection which can do P2P 1G on a Fiber. I bought a RB3011 to firewall this connection and at some point maybe also make a VPN entry to my home-network.

I have the issue, that I do not get the expected ~940Mbps (which I do get with another simple media-converter).

I also noticed that the retries-count doing an iperf3 is pretty high. Now I did two iperfs locally from my laptop to my server. The first one on the same switch-chip (both hooked up on ports ETH6-10).

Here I have a rock solid connection:
$ iperf3 -c 192.168.1.200
Connecting to host 192.168.1.200, port 5201
[  5] local 192.168.1.109 port 56464 connected to 192.168.1.200 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   114 MBytes   958 Mbits/sec    0    652 KBytes       
[  5]   1.00-2.00   sec   112 MBytes   944 Mbits/sec    0    682 KBytes       
[  5]   2.00-3.00   sec   112 MBytes   944 Mbits/sec    0    682 KBytes       
[  5]   3.00-4.00   sec   112 MBytes   944 Mbits/sec    0    682 KBytes       
[  5]   4.00-5.00   sec   111 MBytes   933 Mbits/sec    0    749 KBytes       
[  5]   5.00-6.00   sec   112 MBytes   944 Mbits/sec    0    786 KBytes       
[  5]   6.00-7.00   sec   112 MBytes   944 Mbits/sec    0    824 KBytes       
[  5]   7.00-8.00   sec   112 MBytes   944 Mbits/sec    0    824 KBytes       
[  5]   8.00-9.00   sec   112 MBytes   944 Mbits/sec    0    824 KBytes       
[  5]   9.00-10.00  sec   111 MBytes   933 Mbits/sec    0    867 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  1.10 GBytes   943 Mbits/sec    0             sender
[  5]   0.00-10.00  sec  1.10 GBytes   941 Mbits/sec                  receiver
However now I hook my laptop up on one of ETH6-10 and the server on one of ETH1-5 and I get this:
$ iperf3 -c 192.168.1.200
Connecting to host 192.168.1.200, port 5201
[  5] local 192.168.1.109 port 56468 connected to 192.168.1.200 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   114 MBytes   955 Mbits/sec   21    143 KBytes       
[  5]   1.00-2.00   sec   112 MBytes   940 Mbits/sec    6    276 KBytes       
[  5]   2.00-3.00   sec   112 MBytes   943 Mbits/sec   15    223 KBytes       
[  5]   3.00-4.00   sec   112 MBytes   939 Mbits/sec   26    110 KBytes       
[  5]   4.00-5.00   sec   112 MBytes   942 Mbits/sec   24    226 KBytes       
[  5]   5.00-6.00   sec   112 MBytes   942 Mbits/sec   23    230 KBytes       
[  5]   6.00-7.00   sec   112 MBytes   938 Mbits/sec   26    129 KBytes       
[  5]   7.00-8.00   sec   112 MBytes   939 Mbits/sec   19    256 KBytes       
[  5]   8.00-9.00   sec   112 MBytes   943 Mbits/sec   26   80.6 KBytes       
[  5]   9.00-10.00  sec   112 MBytes   938 Mbits/sec   28   67.9 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  1.10 GBytes   942 Mbits/sec  214             sender
[  5]   0.00-10.02  sec  1.10 GBytes   939 Mbits/sec                  receiver
Has anyone ever seen this or any tips how I can improve the retry count?

And also maybe some advice, how to improve the "only" ~600Mbps get through from SFP to ETH bridge, but CPU only at ~20%?

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