When using the OSPF dynamic routing protocol on an Aruba CX switch, what must match on the neighboring devices to exchange routes?

For two OSPF-enabled routers to form an adjacency and exchange routing information, several parameters on their connecting interfaces must be identical. These include the Area ID, authentication settings (if used), subnet mask, and crucially, the Hello and Dead intervals. The Hello timer dictates how often Hello packets are sent to discover and maintain neighbor relationships. If the Hello or Dead timers do not match between two potential neighbors, they will fail to establish a full adjacency, preventing the exchange of Link-State Advertisements (LSAs) and subsequent route calculation.

B. DR configuration: The Designated Router (DR) is elected on multi-access networks, not configured to match. While priority influences the election, it does not need to be identical on neighbors.
C. ECMP method: Equal-Cost Multi-Path (ECMP) is a local forwarding decision mechanism used when multiple best paths exist; it is not a parameter checked during OSPF adjacency formation.
D. BDR configuration: Similar to the DR, the Backup Designated Router (BDR) is elected based on priority and router ID. The priority values do not need to match between neighbors.

1. ArubaOS-CX 10.12 Routing Guide, Page 338, "OSPF neighbor adjacency": "For two routers to become OSPF neighbors, the following must match: Area ID, Authentication, Hello and Dead intervals, Subnet mask (except for point-to-point links)."

2. RFC 2328 - OSPF Version 2, Section 10.5, "Receiving Hello Packets": This section details the processing of incoming Hello packets. It specifies that the HelloInterval and RouterDeadInterval fields within the packet must match the values configured on the receiving interface for the adjacency to proceed.