In this section, we are going to discussing OSPF(stands for Open Shortest Path First) area. Before entering this topic, we have to know that what is area. This is the portion where an OSPF is divided into. These divisions are called subdomains and these subdomains are referred to as the OSPF area. In other words, we can say that this is a logical collection of the following things:
- OSPF networks
These things should have the same area identification. The things in the area should keep a database, that should keep the information about the area in which it is presented. For example, if the area contains a router, the router must have a database of the information about the area in which the router is presented. Since it keeps the topological database, it reduces the size of the database.
When we divide the OSPF network into multiple areas, each of them should obey some rules. They are listed below:
- A feature called backbone area must be there. This feature is used to combine multiple independent areas into a single domain.
- The next point is that all the areas that are not the backbone area, called the non-backbone area, and all the backbone areas must be connected directly.
- The last rule is that we cannot divide the backbone area, in other words, it cannot be partitioned into small pieces.
Area IDs are used to identify the areas. Suppose, this area-id is represented by using the IP address format or in decimal format, then area 0 can be represented as 0.0.0.0. Suppose that our network has more than one area, then we should name this backbone area as ‘area 0’. The area border router is the router that interfaces different multiple areas.
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- For each are, it has a unique number.
- Even if there is only one area, it will communicate to all the areas that are attached to it.
- The OSPF operations can be enhanced by using the areas. This can be done in larger networks.
- It requires only a small amount of memory if per-area LSDB is smaller.
- Smaller per-area LSDB can be processed by the SPF algorithm, and this only requires fewer CPU cycles, it reduces the convergence tome and it will also reduce the CPU overhead.
- The bandwidth can be reduced by specifying information across the areas.
- By configuring the manual route summarization, the areas will allow a small IP routing table.
OSPF uses a hierarchical design. Commonly, large OSPf uses this hierarchical design. The main reasons for using this design are the following:
- To reduce the routing overhead.
- For faster convergence.
- To converge all the instabilities into a particular area.
To manage the network easily, this network is divided into multiple smaller portions.
Advantages of hierarchical design:
- Reduces the cost(cost for equipment).
- makes design easier.
- Provide more security.
- Traffic multiplexing.
By the hierarchical design of OSPF, we can divide the whole large network into multiple small networks. All these partitioned smaller networks will have the properties explained above(they are, Reduces the cost(cost for equipment), makes design easier, Provide more security, and Traffic multiplexing.)
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