In an OSPF Hello packet what fields must match all neighbor routers on the segment? (Choose 3)

For two OSPF routers on the same segment to form a neighbor adjacency, several parameters in their exchanged Hello packets must match. The Area ID must be identical, as routers can only form adjacencies within the same area on a specific interface. The Hello and Dead Intervals must also match to ensure consistent timing for neighbor health checks. Finally, the area type, indicated by flags like the Stub flag in the Options field of the Hello packet, must be the same. All routers in an area must agree on whether it is a normal, stub, or NSSA area. A mismatch in any of these three parameters will cause the receiving router to discard the Hello packet and prevent an adjacency from forming.

D. DR and BDR addresses: These addresses are learned and agreed upon during the DR/BDR election process; they are not a prerequisite that must match for initial neighbor discovery.
E. The list of neighbors: This field is used to verify bidirectional communication (2-Way state), not a parameter that must match. Each router's list will contain the neighbors it has seen.

1. RFC 2328 - OSPF Version 2: Section 10.5, "Receiving Hello Packets," details the checks performed on an incoming Hello packet. It explicitly lists that the Area ID, HelloInterval, RouterDeadInterval, and Options fields (which contains the Stub area flag, or E-bit) must match the receiving interface's configuration.

2. Nokia 7750 SR OS Router Configuration Guide, Release 21.10.R1: In the "OSPF" chapter, under the "OSPF Hello Protocol" section, it states, "For two routers to become OSPF neighbors, they must agree on the following parameters: Area ID, Authentication, Network mask (on broadcast and NBMA networks), Hello interval, Router dead interval, and Option flags." This directly supports the requirement for Area ID, Hello/Dead intervals, and the Stub flag (within Option flags) to match.

3. Fall 2018, 6.829 Computer Networks Course, MIT OpenCourseWare: Lecture 10 notes on "Routing II: OSPF" describe the OSPF neighbor discovery process. The notes specify that for adjacency formation, routers must agree on the Area ID, Hello/Dead timers, and area options (like the stub flag). This aligns with the standard OSPF requirements.