We would be here covering the basic OSPF concepts as well as their operation. We would explain about the working of OSPF, how to build OSPF tables on an OSPF-enabled router as well as their purpose, OSPF areas, and their importance. Next, we would be covering the OSPF Link State Packet types which would be utilized to exchange data between OSPF routers: LSA (Link State Advertisement), LSDB (Link State Database), LSR (Link State Request), LSAcK (Link State Acknowledgment) and LSU (Link State Update). Later on, we might be taking a look at the OSPF roles: ABR (Area Border Router), ASBR (Autonomous System Boundary Router), DR (Designated Router), Backup DR and much more. So if you wish to have knowledge about all these topics and if you wish to have proper hands-on practice on the same, join our courses at SPOTO to have more knowledge regarding the OSPF. So, let’s begin.
What Is OSPF And How Does It Work?
OSPF is considered as a Link State protocol that’s which would be believed to, may be the most famous protocol among the IGP (Interior Gateway Protocol) family, developed in the midst of 1980s by the OSPF working group of the IETF.
When configured, OSPF would be able to listen to neighbors and gather all link state data available to build a topology map of all available paths in its network and later on save the information in its topology database, which would be also known as its LSDB (Link-State Database).
Utilizing the information from its topology database:
From information which would be gathered, it would be calculating the best shortest path to each reachable subnet or network utilizing an algorithm called SFP (Shortest Path First) which was developed by the computer scientist Edsger W. Dijkstra in the year 1956. OSPF would be then constructing three tables to store the following information:
- Neighbor Table: It would contain all discovered OSPF neighbors with whom routing information will be interchanged
- Topology Table: It would contain the entire road map of the network with all available OSPF routers and calculated best and alternative paths.
- Routing Table: It would contain the current working best paths that will be used to forward data traffic between neighbors.
Understanding OSPF Areas:
OSPF would be offering a very distinguishable feature namely the Routing Areas. It means it would be dividing routers inside a single autonomous system that is running OSPF, into areas where each area would be consisting of a group of connected routers.
The idea of dividing the OSPF network into areas is to simplify the administration as well as optimize the available resources. Resource optimization would be especially important for large enterprise networks with a plethora of network as well as links. Having many routers exchange the link state database could flood the network as well as reduce its efficiency. Thus, this was the need which led to the creation of concept Areas.
Areas which are considered as a logical collection of routers which could be carried to the same Area ID or number inside of an OSPF network, the OSPF network itself could contain multiple areas, the first as well as the main Area would be considered as the backbone area “Area 0”, all other areas should be then connected to Area 0.
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