RB951G-2HnD
RouterOS: 6.19
Firmware: 3.18

When connect any RB port to 100 Mbps network (ISP) - 100% packets loss or no link at all.

Auto negotiation detect 100 Mbit FD, but 99-100% ping packets loss.
Manual 100Mbps - No Link!

Tried connect to 1Gb laptop:
1Gb auto - all fine.
100Mb "auto" (advertise only 100 FD/HD) - packets loss 99-100%.
10Mb "auto" (advertise only 100 FD/HD) - all fine.
1Gb FD/HD manual - all fine.
100Mb FD/HD manual - no link.
10Mb FD/HD manual - all fine.

Replaced mikrotik - same problem.

What happened to these mikrotiks?

Is nothing wrong with network cable?

Cable is ok. Tested with different cables.

This router work fine with atheros LAN card and with D-Link hub on 100M. Possibly my ISP use Huawei router and I think problem only with some devices (My laptop and my ISP router).

is no flow control or jumbo frames enforcements on sides ?
half-duples 100 had same effect ?
then probably there was incompatible phy's. remind me some Marvel vs 3Com wars ~10 years ago, for example.

Flow control On/Off/Auto Rx/Tx 100Mbit FD/HD all combinations tested. Same problems.

Having same issues, i have 200 mbps wan speed, on single download i can cap up to 25MBps, but on multiple downlaods no more than 10-12 MBps(100mbps).

Contacted MT support, they are scratching their heads, told me to reinstall via netinstall, same effect.

P.S cat5e cables, showing rate 1gbps, cpu goes from 10-15% (with fasttrack, default config from MT).

Edit on post after a year: Same router, but cable company changed a modem from cisco to arris.Plus I keep regular update on mikrotik packages.
Works like a charm, it can pump speeds to 1 gbps without any hickups.