Backbone Router – The backbone router runs OSPF and has at least one interface connected to the OSPF backbone area. It is a key component in OSPF that serves as a central point connecting to different area.

Area Border Router (ABR) – This type of router connects one or more areas to the OSPF backbone, it has neighbor relationships with devices in multiple OSPF areas.

Autonomous System Boundary Router (ASBR) – This type of router connects and exchanges routing information between different routing protocols, in our topology we see the ASBR connecting to EIGRP network to the OSPF backbone.

Internal Router – This type of router has neighbor relationships with devices in the same area, in other words it should have all OSPF interfaces belong to the same area.

As we see in the topology that depending on the placement of the router they perform different tasks but a single router can also be a backbone router, an ABR and an ASBR.