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 ISAKMP.


Operation, Administration, and Maintenance. An ATM Forum specification for monitoring ATM virtual connections. OAM performs standard loopback, fault detection and notification, and remote defect identification for each connection, verifying that the connection is up and the router is operational.


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


Network line with a transmission speed of 155.52 Mbps (payload of 150.336 Mbps) using fiber optics. For SDH interfaces, OC3 is also known as STM1.


SONET line with a transmission speed of 622 Mbps using optical fiber.

Open message

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


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


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

Operation, Administration, and Maintenance

See OAM.

operational mode

JUNOS software mode that allows a user to view statistics and information about the router's current operating status.

optical carrier

See OC.


In BGP, an attribute that describes the source of the route.


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.


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


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

OSPF hello packet

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

overlay network

Network design in which 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 layer requires separate management and operation.