I like to name my tracks about relevant things that I am doing currently in life. I am currently studying the **** out of OSPF. What is OSPF? Read below to find out.

Thank you Matt Costello for the collaboration on this track. 

• Link: A link is a network or router interface assigned to any given network. When an interface is added to the OSPF process, it’s considered to be a link. This link, or interface, will have up or down state information associated with it as well as one or more IP addresses. 

• Router ID:  The router ID (RID)  is an IP address used to identify the router. Cisco chooses the router ID by using the highest IP address of all configured loopback interfaces. If no loopback interfaces are configured with addresses, OSPF will choose the highest IP address out of all active physical interfaces. To OSPF, this is basically the “name” of each router. 

• Neighbor: Neighbors  are two or more routers that have an interface on a common network, such as two routers connected on a point-to-point serial link. OSPF neighbors must have a number of common configuration options to be able to successfully establish a neighbor relationship, and all of these options must be configured EXACTLY THE SAME WAY:  Area ID, Stub area flag, Authentication password (if using one) Hello and Dead intervals.

• Adjacency: An adjacency is a relationship between two OSPF routers that permits the direct change of route updates. Unlike EIGRP, which directly shares routes with all of its neighbors, OSPF is really picky about sharing routing information and will directly share routes only with neighbors that have also established adjacencies. And not all neighbors will become adjacent- this depends upon both they type of network and the configuration of the routers. In multi-access networks, routers form adjacencies with designated and backup designated routers. In point-to-point and point-to-multipoint networks, routers form adjacencies with the router on the opposite side of the connection. 

• Designated router: A designated router (DR)  is elected whenever OSPF routers are connected to the same broadcast network to minimize the number of adjacencies formed and to publicize received routing information to and from the remaining routers on the broadcast network or link. Elections are won based upon a router’s priority level, with the one having the highest priority becoming the winner. If there’s a tie, the router ID will be used to break it. All routes on the shared network will establish adjacencies with the DR and the BDR, which ensures that all routers’ topology tables are synchronized. 

• Backup designated router: A backup designated router (DBR). is a hot standby for the DR on broadcast, or Multicast , links, The BDR receives all routing updates from OSPF adjacent routers but does not disperse LSA updates. 

• Hello protocol: The OSPF Hello protocol provides dynamic neighbor discovery and maintains neighbor relationships. Hello packets and Link State Advertisements (LSAs) build and maintain the topological database. Hello packets are addressed to multicast address 224.0.0.5.

• Neighbor-ship database  The neighbor ship database  is a list of all OSPF routers for which Hello packets have been seen. A variety of details, including the router ID and state, are maintained on each router in the neighbor ship database.

• Topological database: The topological database contains information from all of the Link State Advertisement packets that have been received for an area. The router uses the information from the topology database as input into the Dijkstra algorithm that computes the shortest path to every network. NOTE: LSA packets are used to update and maintain the topological database. 

• Link State Advertisement:  A Link State Advertisement (LSA)  is an OSPF data packet containing link-state and routing information that’s shared among OSPF routers. There are different types of LSA packets. An OSPF router will only exchange LSA packets with routers it has established adjacencies for. 

• OSPF areas:  An OSPF area  is a grouping of contiguous networks and routers. All routers in the same area share a common area ID. Because a router can be a member of more than one area at a time, the area ID is associated with specific interfaces on the router. This allows some interfaces to belong to area 1 while the remaining interfaces can belong to area 0. All of the routers within the same area have the same topology table. When configuring this is typically considered the backbone area. Areas also play a role in establishing a hierarchical network organization - something that really enhances the scalability of OSPF. 

• Broadcast (multi-access) Broadcast (multi-access) networks  like Ethernet allow multiple devices to connect to or access the same network, enabling a broadcast ability so a single packet can be delivered to all nodes on the network. In OSPF,  a DR and BDR must be elected for each broadcast multi-access network. 

• No-broadcast multi-access: No-broadcast multi-access (NBMA) networks like Frame Relay, X.25, and Asynchronous Transfer Mode (ATM) allow for multi-access with broadcast ability like Ethernet, NBMA. Networks require special OSPF configuration to work. 

• Point-to-multipoint: Point-to-multipoint is a network topology made up of a series of connections between a single interface on one router and multiple destination routers. All interfaces on all router share the point-to-multipoint connection and belong to the same network. Point-to-multipoint networks can be further classified according to whether they support broadcasts or not. This is important because it defines the kind of OSPF configuration you can deploy. 

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