For some boards, such as Orange Pi/NanoPi, mac address can random changing. To fix it, need to add one string to /etc/network/interfaces

hwaddress ether  where ether – is a mac address in format 00:00:00:00:00:00

Example of part of file /etc/network/interfaces

allow-hotplug eth0
no-auto-down eth0
iface eth0 inet dhcp
    hwaddress 12:34:56:78:90:ab