I know this is an old post, but I was looking for the same information and couldn’t find it anywhere. Here’s what I worked out:
To match only data from dell devices (for example),
Src MAC Address: 00:1A:A0:00:00:00
Src Mac Mask: FF:FF:FF:00:00:00
This rule will match 00:1A:A0:xx:xx:xx
I haven’t tried it, but the mask field seems to be a bit mask, so you should be able to match ranges much like you can with subnet masks.

自動引用通知: RouterOS 教學索引 | Mikrotik元芳