Unit 1: Network Infrastructure
This will allow you to demonstrate your networking skills, knowledge, and abilities, with a focus on enterprise-level switching, routing, and multicast components that support cross-platform (inter)operability and integration with the most recent software-defined technologies.

Introduction to OSPF

OSPF is a routing protocol that is used in a lot of large, complicated networks. It is called an Interior Gateway Protocol (IGP) because it finds the shortest path first. The shortest path first (SPF) algorithm is used to find the best routing path between a source router and a target router. The OSPF Protocol is a link-state routing protocol. Routers use the Dijkstra algorithm to find the best way through the network and share information about the network’s topology with their nearest neighbors.

OSPF protocol is what exactly?

Open Shortest Path First (OSPF) is an acronym for one thing. For IPv4 and IPv6, the OSPF protocol is defined in RFCs 2328 and 5340, respectively. It communicates routing details via IP packets and runs at the OSI model’s network layer.

Routers are essential nodes in any network because they are responsible for directing data packets to their final destinations. The Open Shortest Path First (OSPF) protocol enables routers to share details regarding the topology of a network, such as the connections between nodes and the associated costs related to them. Routers use this data to determine the best and quickest ways to send data.

When it comes to complex and massive networks, OSPF Protocol is the way to go because of its many useful characteristics. Here are a few examples:

  • Because of this, the network may be segmented into smaller sections, which in turn minimizes the quantity of routing information that each router needs to analyze and store. Each area is connected to neighboring areas through the use of an area border router, often known as an ABR. All of the other areas are connected to the backbone area, also known as area 0, which is the core of the OSPF network.
  • Securing communication between routers and preventing updates that are malicious or unauthorized are both benefits of this feature.

In order to deliver routing updates to all of the routers that are located in the same area or network, it makes use of multicast addresses. As a result, bandwidth consumption is decreased.

Below are the OSPF Terms

Router ID: A router’s Router ID is its active IP address and is used as the router’s active IP address when loopback is not set up. If that doesn’t happen, the highest loopback address is used instead of the current IP address.

Router Priority: This is an 8-bit number that tells the router running OSPF how to choose between DR and BDR in the broadcast network.

The designated router (DR): is chosen to reduce the number of adjacent locations that are close to each other and gives LSAs to all routers. When the DBD is chosen in the broadcast network, all nodes send it out. When there is a broadcast network, the router asks the DR for an update, and the DR replies with an update.

Backup Designated Router (BDR): When the primary DR in a broadcast network goes down, the secondary DR, also known as the backup designated router (BDR), steps in to take over the first DR’s responsibilities.

DR and BDR elections: Broadcast or multi-access networks are the ones in which there is DR and BDR election. Here are the selection criteria:

  • A router will be declared with a higher DR status if its router priority is high.
  • In case of a tie, the larger route should be taken into account when router priority is being determined. When no loopback is set up, the router’s interface with the most active IP address is taken into account. If not, the hyperactive IP address is considered after the highest loopback address.

How Does the OSPF Operate?

Because Open Shortest Path First (OSPF) is a link-state routing protocol, it is necessary for every router in the network to have a database that contains information on the state of every link (interface) in the network. This particular database is known as the link-state database (LSDB), and it includes information similar to the following:

  • Each network router’s ID number
  • Each interface’s IP address and subnet mask
  • The metric cost of every interface
  • The type and state of each interface
  • The neighboring routers on each interface are referred to as neighbors.

 

Every router updates its local state database (LSDB) and updates its neighbors with this information through link-state advertisements (LSAs). Once one router in the network has received and stored an LSA in its LSDB, the next router in the network will receive and store an LSA as well. To make sure that every router is looking at the same network topology, this technique is known as link-state synchronization.

Next, every router in the network uses the data from the LSDB to determine the optimal route to each destination by executing a shortest-path algorithm, like Dijkstra’s algorithm. This route takes into account the cost of each link, which can be set manually or calculated using variables like load, delay, reliability, and bandwidth. A table known as the routing table contains the interface and next-hop router for each destination, as well as the result of this OSPF cost computation.

How OSPF Forms Connections with Neighbors

OSPF routers need to become neighbors with each other before they can share routing information. To do this, hello messages are sent to every interface that is set up for OSPF Protocol. These kinds of things are in hello packets:

  • The sender’s router ID

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