Chapter 21 - Understanding OSPF Concepts

2-way state

In OSPF, a neighbor state that implies that the router has exchanged Hellos with the neighbor and that all required parameters match.

Area Border Router

A router using OSPF in which the router has interfaces in multiple OSPF areas.

backbone area

In OSPFv2 and OSPFv3, the special area in a multiarea design, with all nonbackbone areas needing to connect to the backbone area, area 0.

backup designated router

An OSPF router connected to a multiaccess network that monitors the work of the designated router (DR) and takes over the work of the DR if the DR fails

convergence

The time required for routing protocols to react to changes in the network, removing bad routes and adding new, better routes so that the current best routes are in all the routers' routing tables

dead interval

In OSPF, a timer used for each neighbor. A router considers the neighbor to have failed if no Hellos are received from that neighbor in the time defined by the timer.

designated router

In OSPF, on a multiaccess network, the router that wins an election and is therefore responsible for managing a streamlined process for exchanging OSPF topology information between all routers attached to that network.

distance vector

The logic behind the behavior of some interior routing protocols, such as RIP. Distance vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance vector routing algorithms can be prone to routing loops but are computationally simpler than link-state routing algorithms.

full state

In OSPF, a neighbor state that implies that the two routers have exchanged the complete (full) contents of their respective LSDBs.

fully adjacent

In OSPF, a characterization of the state of a neighbor in which the two neighbors have reached the full state

Hello Interval

With OSPF and EIGRP, an interface timer that dictates how often the router should send Hello messages.

interior gateway protocol (IGP)

A routing protocol designed to be used to exchange routing information inside a single autonomous system

internal router

In OSPF, a router with all interfaces in the same nonbackbone area

link-state

A classification of the underlying algorithm used in some routing protocols. Link-state protocols build a detailed database that lists links (subnets) and their state (up, down), from which the best routes can then be calculated.

link-state advertisement (LSA)

In OSPF, the name of the data structure that resides inside the LSDB and describes in detail the various components in a network, including routers and links (subnets).

link-state database (LSDB)

In OSPF, the data structure in RAM of a router that holds the various LSAs, with the collective LSAs representing the entire topology of the network

link-state update

An OSPF packet used to send an LSA to a neighboring router.

metric

A unit of measure used by routing protocol algorithms to determine the best route for traffic to use to reach a particular destination.

multiarea OSPF

In OSPFv2 and OSPFv3, a design that uses more than one area within one OSPF domain (typically a single company)

neighbor

In routing protocols, another router with which a router decides to exchange routing information

router ID (RID)

In EIGRP and OSPF, a 32-bit number, written in dotted decimal, that uniquely identifies each router.

Shortest Path First algorithm

The name of the algorithm used by link-state routing protocols to analyze the LSDB and find the least-cost routes from that router to each subnet

single-area OSPF

In OSPFv2 and OSPFv3, a design that uses a single area within one OSPF domain (typically a single company)

OSPF Database Description

OSPF packet used to send a list of known LSAs to another router, for that router to check against and request any LSAs that it may be missing from its LSDB