The OSPF 2-Way state signifies that two routers have established bidirectional communication by seeing their own Router ID in the other's Hello packet. For the state machine to reach this point, fundamental parameters within the Hello packets must already match.

A router ID conflict (C) is a critical error where a router receives a Hello packet containing its own ID as the sender. This packet is immediately dropped, and the adjacency will not form, let alone get stuck in a stable state.

The N-bit and E-bit being the same (D) is a required condition for establishing an OSPF adjacency. This represents a correct configuration and, by definition, cannot be the cause of a failure.

A. Hello time values are different.

A mismatch in Hello or Dead timers causes the receiving router to discard the Hello packet, preventing the neighbor relationship from progressing beyond the Down or Init state.

B. Area IDs are different.

A router will discard any Hello packet received on an interface with a non-matching Area ID. This prevents the neighbor relationship from ever being established.

1. RFC 2328 - OSPF Version 2

Section 10.5

"Receiving Hello Packets": This section specifies the processing rules for incoming Hello packets. It explicitly states that if the HelloInterval

RouterDeadInterval

or AreaID in the packet does not match the values configured for the receiving interface

the packet must be dropped. It also states that if the source OSPF Router ID is the same as the receiver's

the packet should be discarded. This confirms that conditions A

B

and C prevent the adjacency from reaching the 2-Way state.

2. Huawei HedEx HCIP-Datacom-Advanced Routing & Switching Technology V1.0 Training Material

"OSPF Fault