O

Oakley

A key determination protocol based on the Diffie-Hellman algorithm that provides added security, including authentication. Oakley was the key-exchange algorithm mandated for use with the initial version of ISAKMP, although various algorithms can be used. Oakley describes a series of key exchanges called 'modes' and details the services provided by each; for example, Perfect Forward Secrecy for keys, identity protection, and authentication. See also Internet Security Association and Key Management Protocol (ISAKMP).

Open message

BGP message that allows two neighbors to negotiate the parameters of the peering session.

OpenConfirm

BGP neighbor state that shows a valid Open message was received from the remote peer.

OpenSent

BGP neighbor state that shows an Open message was sent to the remote peer and the local router is waiting for an Open message to be returned.

Open Shortest Path First (OSPF)

A link-state IGP that makes routing decisions based on the shortest path first (SPF) algorithm (also referred to as the Dijkstra algorithm).

Open System Interconnection (OSI)

Standard reference model for how messages are transmitted between two points on a network.

operational mode

JUNOS software mode allowing a user to view statistics and information concerning the router's current operating status.

Optical Carrier (OC)

In SONET, Optical Carrier levels indicate the transmission rate of digital signals on optical fiber.

Origin

BGP attribute that describes the believability of a particular route. The router that first places the route into BGP should attempt to accurately describe the source of the route.

orlonger

JUNOS software routing policy match type that represents all routes more specific than the given subnet, including the given subnet itself. It is similar to a mathematical greater-than-or-equals-to operation.

OSPF Hello packet

Message sent by each OSPF router to each adjacent neighbor. It is used to establish and maintain the router's neighbor relationships.

overlay network

Network design seen where a logical Layer 3 topology (IP subnets) is operating over a logical Layer 2 topology (ATM PVCs). Layers in the network do not have knowledge of each other, and each requires separate management and operation.