If a Router originates a type 1 router LSA with the E bit set what types of areas can it belong to? Select all that apply.

The 'E' bit in an OSPF Type 1 Router LSA is the "External" bit. When set, it signifies that the originating router is an Autonomous System Boundary Router (ASBR). An ASBR is a router that injects external routing information into the OSPF domain. Standard and Backbone Areas fully support ASBRs and the associated Type 5 External LSAs. Not-So-Stubby Areas (NSSAs) are a special area type designed to permit the existence of an ASBR. The ASBR in an NSSA originates Type 7 LSAs for its external routes and sets the 'E' bit in its Type 1 LSA to advertise its ASBR role. Therefore, a router setting the 'E' bit can belong to a standard area, the backbone area, or an NSSA.

B. Stub Area: A stub area, by definition, does not accept external route advertisements (Type 4 and 5 LSAs). Consequently, an ASBR cannot reside within a stub area. ---

1. Nokia 7750 SR OS Router Configuration Guide, Release 22.10.R1: In the "OSPF Areas" chapter, the section on "Stub Areas" states: "An ASBR is a router that advertises external routes into OSPF. ASBRs are not allowed in stub areas." This confirms that option B is incorrect.

2. Nokia 7750 SR OS Router Configuration Guide, Release 22.10.R1: In the "OSPF Areas" chapter, the section on "Not-So-Stubby Areas (NSSAs)" describes their function: "NSSAs are similar to stub areas in that they do not accept type 5 LSAs... However, unlike stub areas, NSSAs can have an ASBR." This confirms that an ASBR, which sets the 'E' bit, can exist in an NSSA (Option A).

3. RFC 2328, OSPF Version 2: Section 12.4.1, "The Router-LSA," defines the bits in the LSA options field. It specifies: "E-bit: This bit is set if the router is an ASBR (Autonomous System Boundary Router)." This defines the meaning of the 'E' bit.

4. RFC 3101, The OSPF Not-So-Stubby Area (NSSA) Option: Section 2.1, "NSSA AS boundary routers," states: "An NSSA AS boundary router is an AS boundary router that is attached to an NSSA. Such a router must set the E-bit in its router-LSAs that are originated into the NSSA." This explicitly links the 'E' bit to ASBRs within an NSSA.