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AS Boundary Router (ASBR)
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A router attached at the edge of an OSPF network is considered an AS Boundary Router (ASBR). An ASBR generally has one or more interfaces that run an Inter-Domain Routing Protocol (IDRP) such as BGP. In addition, any router distributing static routes or RIP routes into OSPF is considered an ASBR. The ASBR forwards routes learned from IDRP into the OSPF domain. In this way, routers inside the OSPF network learn about destinations outside their domain.
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Area Border Router (ABR)
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A router attached to two or more areas inside an OSPF network is considered an Area Border Router (ABR). ABRs play an important role in OSPF networks by limiting the amount of OSPF information that gets disseminated.
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Internal Router (IR)
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A router that only has interfaces within a single area inside an OSPF network is considered an Internal Router (IR). Unlike ABRs, IRs have topological information only about the area in which they are contained.
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Designated Router (DR)
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In a broadcast network, such as an Ethernet network that has more than one router locally attached, a single router is elected to be the Designated Router (DR) for that broadcast network. A DR assumes the responsibility of making sure all routers on the broadcast network are in synchronization with one another.
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Backup Designated Router (BDR)
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In a broadcast network, such as an Ethernet network, a Backup Designated Router (BDR) is elected in addition to the Designated Router (DR). The BDR can assume essentially the same responsibilities as the DR; if the DR fails, the BDR will assume the role of the DR in the broadcast network.
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Other router (OR)
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In a broadcast network, such as an Ethernet network, any router not elected to be a Designated Router (DR) or Backup Designated Router (BDR) is considered to be an other router (OR).
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