root@bananapim2plus:~# ethtool -s eth0 speed 100 duplex full
root@bananapim2plus:~# ethtool eth0
Settings for eth0:
        Supported ports: [ TP MII ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Supported pause frame use: No
        Supports auto-negotiation: Yes
        Advertised link modes:  100baseT/Full
        Advertised pause frame use: No
        Advertised auto-negotiation: Yes
        Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                             100baseT/Half 100baseT/Full
                                             1000baseT/Full
        Link partner advertised pause frame use: Symmetric Receive-only
        Link partner advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: MII
        PHYAD: 0
        Transceiver: external
        Auto-negotiation: on
        Current message level: 0x00000000 (0)

        Link detected: yes
root@bananapim2plus:~# mii-tool -v
eth0: negotiated 1000baseT-FD flow-control, link ok
  product info: vendor 00:07:32, model 17 rev 5
  basic mode:   autonegotiation enabled
  basic status: autonegotiation complete, link ok
  capabilities: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
  advertising:  1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
  link partner: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
root@bananapim2plus:~# iperf3 -s
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Accepted connection from 192.168.83.95, port 53564
[  5] local 192.168.83.77 port 5201 connected to 192.168.83.95 port 53565
[ ID] Interval           Transfer     Bandwidth
[  5]   0.00-1.00   sec   105 MBytes   884 Mbits/sec
[  5]   1.00-2.00   sec   112 MBytes   940 Mbits/sec
[  5]   2.00-3.00   sec   112 MBytes   940 Mbits/sec
[  5]   3.00-4.00   sec   112 MBytes   940 Mbits/sec
[  5]   4.00-5.00   sec   112 MBytes   940 Mbits/sec
[  5]   5.00-6.00   sec   112 MBytes   940 Mbits/sec
[  5]   6.00-7.00   sec   112 MBytes   940 Mbits/sec
[  5]   7.00-8.00   sec   112 MBytes   940 Mbits/sec
[  5]   8.00-9.00   sec   112 MBytes   940 Mbits/sec
[  5]   9.00-10.00  sec   112 MBytes   940 Mbits/sec
[  5]  10.00-10.01  sec   737 KBytes   931 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth
[  5]   0.00-10.01  sec  1.09 GBytes   935 Mbits/sec                  sender
[  5]   0.00-10.01  sec  1.09 GBytes   935 Mbits/sec                  receiver
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
^Ciperf3: interrupt - the server has terminated