I haven't done anything with passive. The MT wiki says passive doesn't send or receive OSPF traffic. Why not just call it disabled, then?
Passive means that the router will not form adjacencies on the interface, but the interface is still connected to a network which is "interior" to your routing domain. I.e. - the interface's connected network will be originated into OSPF.
This distinction passes by a lot of people on here because it's extremely common (sadly) for people to just do the lazy method of redistributing connected routes into OSPF. This is a bad habit to get into. There are very few situations where you must redistribute connected. The reasons why this is bad involve lots of OSPF theory and design best practices, and many Mikrotik users will not ever have networks that grow large enough that they will be truly hampered by the problems that tons of external routes can cause. . . but if you start off with the right habits from the beginning, then your transition into larger networks will not be difficult.
You'll find that I've been pretty vocal about this recently - but it's only because I want to help spread good practices to people as they learn more advanced routing skills.
