Please help. I have a stable server with x86 on MK 2.9.42, no crashes no system downs with 4 cards 100Mbit/sec full duplex mode.
2 x intel pro/1000 network cards works propertly on 100Mbit mode. But, i want to do 1Gbit with Intel PRO/1000 (not fiber), and when i change cable conecctions (physical from 100Mbit switch to 1Gb switch) link is UP packets going normaly, but after 5-10 secons MK is crashes and reboot.
System updating to 3.7 not solved the problem.

Other two card is
1: 3com 3c59x pci
2: integrated to mb RealTek RTL8169 Gigabit Ethernet

from documentation i got info:
* RealTek RTL8169 Gigabit Ethernet (not recommended: may lock up the router)

maybe here problem? May be disabling of RealTek RTL8169 in BIOS solves the problem?

We aren't seeing an issue with the Intel cards and 3.7.

Never have been any problems with intel cards, both 100M and 1G. Now using 3.7 with 3 Intel 1000MT Cards. Very stable.
RTL 8169 has serious issues with stability on Mikrotik.