I've got answer from support. I put it here if someone will looking for the same problem. > Unfortunately, your devices has HW issue which is described here: > https://forum.mikrotik.com/viewtopic.php?f=13&t=97755&p=699766&hilit=t > v#p699766 > > We fixed this issue to all RB951G-2HnD de...

upgrade your RB to latest "long term" ROS, which is 6.42.10 (your version is pretty old). That includes both ROS and firmware upgrade.

it's my mistake. i have "current" version 6.43.4 (last stable).
ok. it's time to write support. tnx

So nobody can help me?
Support don't work on forum? Should I write directly to support?

Tecra M9 had 1Gbit/s Intel ethernet card

So strange... I've thought there is some issue with 100 Mbps clients. You talking about 1G and same problem. I'm surprised.

router Nexx connecting to Mikrotik on 100Mbps fullduplex. I've checked from Winbox - connection ok, manual setting - only 100Mbps fullduplex.
Also tested speed (through nexx): SmartTV 76-96Mbps, wifi connection (nexx wlan) 45-55Mbps, usb-eth speed 5-7Mbps because usb 1.1.

ohhhh. and did you try another 100 Mbps equipment in the same port? Ah! Forgot... I've tried also another router (NEXX, 100mbps) to connect via WAN-port to LAN-port (Mikrotik) - it connects succefully. In this case SmartTV and usb-eth-card got IPs from Mikrotik over dhcp. PS: I've found and read al...

Has you tried another cable?

Yes, i've used 3 different cables, and one was new cat7.

Hi! I cannot understand what's wrong: 100Mbps client works only on 10Mbps halfduplex on RB951G-2HND firmware ver. 6.34 (or some latest available), router bought 3-4 years ago. All eth ports working fine with 2 PC which have 1G eth ports (autonegotiation "on", advertise 10/100/1000 Mbps) on...