An OSPF ASBR must have at least one interface in the backbone area (area 0)

An OSPF Autonomous System Boundary Router (ASBR) is not required to have an interface in the backbone area (Area 0). An ASBR's function is to inject external routes into the OSPF domain. It can be located in any type of OSPF area (backbone, standard, stub, or NSSA). When an ASBR resides within a non-backbone area, the Area Border Router (ABR) for that area is responsible for advertising reachability to the ASBR. The ABR does this by originating a Type 4 Summary-ASBR Link State Advertisement (LSA) and flooding it into the backbone area. This Type 4 LSA allows routers in other areas to learn the path to the ASBR and subsequently use the external routes (advertised in Type 5 LSAs) that the ASBR provides. The requirement to connect to Area 0 applies to ABRs, not necessarily to ASBRs.

The statement "True" is incorrect because it conflates the architectural requirements of an Area Border Router (ABR) with those of an ASBR. While an ABR must, by definition, have an interface in Area 0 to connect other areas to the backbone, an ASBR has no such constraint. The OSPF protocol design explicitly includes the Type 4 LSA mechanism to support ASBRs located in non-backbone areas.

1. RFC 2328, OSPF Version 2: Section 3.5, "AS boundary routers", states: "An AS boundary router is a router that exchanges routing information with routers belonging to other Autonomous Systems... AS boundary routers can be located in any of the areas in the OSPF Autonomous System." This is the definitive protocol specification.

2. Nokia 7750 SR OS OSPF and IS-IS Guide, Release 21.x: In the section "OSPF LSA Types", the description of "ASBR-Summary-LSAs (Type 4)" explains their purpose: "ASBR-summary-LSAs are originated by ABRs and describe a route to an ASBR. An ASBR-summary-LSA is flooded into the backbone... This LSA type is required when an ASBR is located in a non-backbone area." This official vendor documentation confirms the mechanism that allows an ASBR to exist outside of Area 0.

3. Doyle, J., & Carroll, J. (2006). Routing TCP/IP, Volume 1 (2nd ed.). Cisco Press. Chapter 8, "OSPF," in the section "OSPF LSA Types," explains that a Type 4 LSA is generated by an ABR to advertise an ASBR in one of its attached areas to the rest of the OSPF domain. This is a standard, academically-recognized text used in university-level networking courses.