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I have a strange behaviour in my Fedora 31:

After a reboot, the network works like a charm. After some seconds, I get varying network speed and latency. Please see the iperf scan and ping analysis:

64 bytes from 192.168.0.7: icmp_seq=85 ttl=64 time=0.377 ms
64 bytes from 192.168.0.7: icmp_seq=86 ttl=64 time=0.380 ms
64 bytes from 192.168.0.7: icmp_seq=87 ttl=64 time=0.356 ms
64 bytes from 192.168.0.7: icmp_seq=88 ttl=64 time=0.284 ms
64 bytes from 192.168.0.7: icmp_seq=89 ttl=64 time=0.276 ms
64 bytes from 192.168.0.7: icmp_seq=90 ttl=64 time=0.234 ms
64 bytes from 192.168.0.7: icmp_seq=91 ttl=64 time=0.293 ms
64 bytes from 192.168.0.7: icmp_seq=92 ttl=64 time=4329 ms
64 bytes from 192.168.0.7: icmp_seq=93 ttl=64 time=3304 ms
64 bytes from 192.168.0.7: icmp_seq=94 ttl=64 time=2280 ms
64 bytes from 192.168.0.7: icmp_seq=95 ttl=64 time=1257 ms
64 bytes from 192.168.0.7: icmp_seq=96 ttl=64 time=233 ms
64 bytes from 192.168.0.7: icmp_seq=97 ttl=64 time=2145 ms
64 bytes from 192.168.0.7: icmp_seq=98 ttl=64 time=1098 ms
64 bytes from 192.168.0.7: icmp_seq=99 ttl=64 time=74.5 ms
64 bytes from 192.168.0.7: icmp_seq=100 ttl=64 time=294 ms
64 bytes from 192.168.0.7: icmp_seq=105 ttl=64 time=6029 ms
64 bytes from 192.168.0.7: icmp_seq=106 ttl=64 time=5005 ms
64 bytes from 192.168.0.7: icmp_seq=107 ttl=64 time=3981 ms
64 bytes from 192.168.0.7: icmp_seq=108 ttl=64 time=2956 ms
64 bytes from 192.168.0.7: icmp_seq=109 ttl=64 time=1933 ms
64 bytes from 192.168.0.7: icmp_seq=110 ttl=64 time=909 ms
64 bytes from 192.168.0.7: icmp_seq=111 ttl=64 time=0.362 ms
64 bytes from 192.168.0.7: icmp_seq=112 ttl=64 time=0.295 ms
64 bytes from 192.168.0.7: icmp_seq=113 ttl=64 time=0.297 ms
64 bytes from 192.168.0.7: icmp_seq=114 ttl=64 time=0.300 ms
64 bytes from 192.168.0.7: icmp_seq=115 ttl=64 time=0.316 ms
64 bytes from 192.168.0.7: icmp_seq=116 ttl=64 time=0.381 ms
64 bytes from 192.168.0.7: icmp_seq=117 ttl=64 time=0.376 ms

And here the iperf:

% iperf -c 192.168.0.7 -e -i 1
------------------------------------------------------------
Client connecting to sun.beach.lan, TCP port 5001 with pid 12703
Write buffer size:  128 KByte
TCP window size:  450 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.105 port 42752 connected with 192.168.0.7 port 5001 (ct=0.30 ms)
[ ID] Interval        Transfer    Bandwidth       Write/Err  Rtry     Cwnd/RTT        NetPwr
[  3] 0.00-1.00 sec  78.7 MBytes   660 Mbits/sec  630/0          0       76K/566 us  145820.76
[  3] 1.00-2.00 sec   382 KBytes  3.13 Mbits/sec  3/1          1        1K/80125 us  4.88
[  3] 2.00-3.00 sec  0.00 Bytes  0.00 bits/sec  0/2          0        1K/80125 us  0.00
[  3] 3.00-4.00 sec   191 KBytes  1.56 Mbits/sec  2/1          0      596K/2243533 us  0.09
[  3] 4.00-5.00 sec  0.00 Bytes  0.00 bits/sec  0/2          0      596K/2243533 us  0.00
[  3] 5.00-6.00 sec  0.00 Bytes  0.00 bits/sec  0/2          0      596K/2243533 us  0.00
[  3] 6.00-7.00 sec  0.00 Bytes  0.00 bits/sec  0/2          0      596K/2243533 us  0.00
[  3] 7.00-8.00 sec  0.00 Bytes  0.00 bits/sec  0/2          0      596K/2243533 us  0.00
[  3] 8.00-9.00 sec  0.00 Bytes  0.00 bits/sec  0/2          0      596K/2243533 us  0.00
[  3] 9.00-10.00 sec  0.00 Bytes  0.00 bits/sec  0/2          0      596K/2243533 us  0.00
[  3] 0.00-10.25 sec  79.3 MBytes  64.9 Mbits/sec  635/16          1       -1K/1586554 us  5.11

Both machines and connected via unmanaged gigabit ethernet switch. Its the only system, what has problems.

I already tried different cables, different medium (Powerline, LAN over WiFi), different switch. But every time I get the some problem. In the worst cases, the NIC doesnt recognize the plugged cable anymore.

At the moment I suspect my NIC.

Does anyone have a suggestion, where to start troubleshooting?

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What if you plug directly another computer to your computer and you repeat the different tests with a strong ethernet wire (cat6 for example) ?

It looks like a problem on the ethernet wire

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  • I did some research and found it, it happens everytime I transfer large files > 200MB. I tested a Live-Image of Fedora 31 and had no issues. I reinstalled my workstation and now everything works as expected. – beacher_pille88 Nov 10 '19 at 19:48
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The reason is still unclear.

A fresh installation solved the issue.

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