OSPF introduces several router types related to their place in the area architecture. Figure 6-5 displays a diagram of OSPF router types.
Figure 6-5 OSPF Router Types
The following is a list of explanations for each router type shown in Figure 6-5:
• Internal router—All routers whose interfaces belong to the same OSPF area. These routers keep only one link-state database.
• Area border router (ABR)—Routers that are connected to more than one area. These routers maintain a link-state database for each area to which they belong.
• Autonomous system boundary router (ASBR)—Routers that inject external link-state advertisements into the OSPF database. These external routes are learned either via other routing protocols or as static routes.
• Backbone router—Routers with at least one interface attached to Area 0. Note that a router can be an ABR, ASBR, and backbone router at the same time.
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