Do you have a USB 3.0 port available?

Have two D-Link USB 3.0 to Gigabit Ethernet Adapters Model DUB-1312 here. Uses the ClearOS 7.x ax88179_178a in-built driver.

Using ClearOS 7.7.2 gw (192.168.1.26)

  3] local 192.168.1.84 port 47258 connected with 192.168.1.26 port 5001

[ ID] Interval       Transfer     Bandwidth

[  3]  0.0-10.0 sec  1.07 GBytes   921 Mbits/sec



[  3] local 192.168.1.26 port 34786 connected with 192.168.1.84 port 5001

[ ID] Interval       Transfer     Bandwidth

[  3]  0.0-10.0 sec  1.10 GBytes   943 Mbits/sec

As you can see - very little difference in either direction... and close to the theretical maximum...
Host Intel i7-3770 - ClearOS - Intel 82574L NIC
Client an old AMD FX-4100 - Fedora - D-link USB DUB 1312 NIC

Edit - added host and client NIC models

I think it's a cheap NIC, so i will buy another one, and retry.

I did not recognise your first NIC. I think it looks OK. Can you try "lspci -knn | grep Eth"?

Your USB NIC is a problem. Look at the "Rx errors" line. Start with changing the cable. What is the output of "lsusb"? Also what driver is it using ("ethtool -i enp0s18f0u3)?

External - Static

03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL810xE PCI Express Fast Ethernet controller (rev 05)

	Subsystem: Hewlett-Packard Company Device 188b

	Kernel driver in use: r8169

	Kernel modules: r8169

[root@server ~]# ethtool enp0s18f0u3

Settings for enp0s18f0u3:

	Supported ports: [ TP MII ]

	Supported link modes:   10baseT/Half 10baseT/Full 

	                        100baseT/Half 100baseT/Full 

	Supported pause frame use: No

	Supports auto-negotiation: Yes

	Supported FEC modes: Not reported

	Advertised link modes:  10baseT/Half 10baseT/Full 

	                        100baseT/Half 100baseT/Full 

	Advertised pause frame use: Symmetric Receive-only

	Advertised auto-negotiation: Yes

	Advertised FEC modes: Not reported

	Link partner advertised link modes:  10baseT/Half 10baseT/Full 

	                                     100baseT/Half 100baseT/Full 

	Link partner advertised pause frame use: Symmetric Receive-only

	Link partner advertised auto-negotiation: Yes

	Link partner advertised FEC modes: Not reported

	Speed: 100Mb/s

	Duplex: Full

	Port: MII

	PHYAD: 0

	Transceiver: internal

	Auto-negotiation: on

	Current message level: 0x00000007 (7)

			       drv probe link

	Link detected: yes

[root@server ~]# ifconfig

enp0s18f0u3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

        inet 10.50.100.1  netmask 255.255.255.0  broadcast 10.50.100.255

        inet6 fe80::2e0:4cff:fe53:4458  prefixlen 64  scopeid 0x20<link>

        ether 00:e0:4c:53:44:58  txqueuelen 1000  (Ethernet)

        RX packets 841843  bytes 216376707 (206.3 MiB)

        RX errors 23185  dropped 2055  overruns 1746  frame 18900

        TX packets 1217506  bytes 1369569494 (1.2 GiB)

        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0



enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500

        inet 70.67.177.218  netmask 255.255.0.0  broadcast 70.67.255.255

        inet6 fe80::d6c9:efff:fe7f:38ef  prefixlen 64  scopeid 0x20<link>

        ether d4:c9:ef:7f:38:ef  txqueuelen 1000  (Ethernet)

        RX packets 2966773  bytes 1822216334 (1.6 GiB)

        RX errors 0  dropped 0  overruns 0  frame 0

        TX packets 906668  bytes 250920226 (239.2 MiB)

        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0



lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536

        inet 127.0.0.1  netmask 255.0.0.0

        inet6 ::1  prefixlen 128  scopeid 0x10<host>

        loop  txqueuelen 1000  (Local Loopback)

        RX packets 33678  bytes 13232180 (12.6 MiB)

        RX errors 0  dropped 0  overruns 0  frame 0

        TX packets 33678  bytes 13232180 (12.6 MiB)

        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

"Yes, cable, connector/SFP, link or NIC issue (in the order of most probable) is the most common cause for rx errors."
https://serverfault.com/questions/918796/high-rx-and-dropped-errors

What sort of link external do you have? DHCP, Static or PPPoE? What is the output of

lspci -k | grep Eth -A 3

Also do you see any errors in "ifconfig"?

I believe the replacement for mii-tool is ethtool.