Which OSPF packet type is used to establish and maintain neighbor relationships between OSPF routers?

OSPF Hello packets are sent periodically out of OSPF-enabled interfaces to discover, establish, and maintain neighbor relationships. These packets contain information such as the Router ID, Hello/Dead intervals, area ID, and authentication data. If two routers agree on these parameters, they become neighbors. The continued reception of Hello packets confirms that the neighbor is still active and reachable.

A. Link-State Advertisements (LSAs) are data structures that describe the local state of a router or network; they do not establish neighbor relationships.

B. Link-State Update (LSU) packets are used to flood LSAs to other routers after neighbor adjacencies are already formed.

C. Database Description (DBD) packets are exchanged after a neighbor relationship is established to synchronize the link-state databases.

1. Juniper Networks TechLibrary. (2023). Understanding OSPF Packet Types. Junos OS Documentation. Retrieved from https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/concept/ospf-packet-types-understanding.html. (See the description for "Hello packets").

2. Moy

J. (1998). RFC 2328: OSPF Version 2. The Internet Society. Section 4.2

"The OSPF Packet Header"

and Section 10.5

"Receiving Hello Packets". Retrieved from https://datatracker.ietf.org/doc/html/rfc2328.