When you're preparing to pass the BSCI exam on the way to the coveted Cisco CCNP certification, you can be quickly overwhelmed by the sheer amount of BGP and OSPF knowledge you must demonstrate a mastery of. One set of details that some BSCI and CCNP candidates underestimate are the differences between the OSPF router types. The OSPF router types seem straightforward enough, but what you must keep in mind is that a router can fill more than one of these roles!