r An internal router resides completely within a single area within a single OSPF autonomous system. Area border router (ABR) An ABR resides in more than one area within a single OSPF autonomous system. Autonomous system border router (ASBR) An ASBR connects to multiple OSPF autonomous systems, or to an OSPF auton- omous system and another routing protocol's autonomous system. Backbone routers Backbone routers in area zero. Area zero is considered the backbone in an OSPF network. Designated router (DR) The DR is the router on a broadcast network that is elected to do the brunt of the OSPF processing. The DR will update all the other routers in the area with routes. Backup designated router (BDR) The BDR is the router most eligible to become the DR should the DR fail. Unlike other routing protocols, OSPF does not send routes, but rather link state ad- vertisements (LSAs). Each OSPF router determines which routes to use based on an internal database compiled from these LSAs. There are six LSA types: Router LSAs (type 1) Router LSAs are sent by every OSPF router into each connected area. These ad- vertisements describe the router's links within the area. Network LSAs (type 2) Network LSAs are sent by DRs and describe the routers connected to the network from which the LSA was received. Summary LSAs for ABRs (type 3) Summary LSAs for ABRs are sent by ABRs. These advertisements describe interarea routes for networks. They are also used to advertise summary routes. Summary LSAs for ASBRs (type 4) Summary LSAs for ASBRs are sent by ASBRs and ABRs. These advertisements describe links to ASBRs. Chapter 10: Routing Protocols Autonomous System External (ASE) LSAs (type 5) ASE LSAs are sent by ASBRs and ABRs. These advertisements describe networks external to the autonomous system. They are sent everywhere except to stub areas. Not So Stubby Area (NSSA) LSAs (type 7) NSSA LSAs are sent by NSSA ASBRs. Since type-5 LSAs are not allowed within the NSSA, type-7 LSAs are sent instead and stay within the NSSA. Type-7 LSAs get conv