OSPF Special Areas

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OSPF areas and Special Areas Use in Networking:

1. Scalability: As networks grow, the number of routers and links can increase exponentially. This can lead to large routing tables and high CPU utilization due to frequent SPF calculations. By dividing a network into smaller areas, OSPF can limit the impact of topology changes and keep routing tables manageable.

2. Reduced Routing Traffic: OSPF uses Link State Advertisements (LSAs) to share information about network topology. By confining LSAs within an area, OSPF can reduce routing traffic across the network.

3. Security and Administrative Control: Areas can be used to implement administrative boundaries within a network, allowing different departments or locations to manage their own networks.

Now, let's discuss the special areas in OSPF:

Stub Area: A stub area is an area that does not accept external LSAs. This means that routers in a stub area only know about networks within their area and a default route to the rest of the network. This can significantly reduce the size of the routing table.

Totally Stub Area: A totally stub area is similar to a stub area, but it also does not accept summary LSAs. This means that routers in a totally stub area only know about networks within their area and a default route to the rest of the network.

NSSA (Not So Stubby Area): An NSSA is a type of stub area that can import external routes as type 7 LSAs, which are then converted to type 5 LSAs at the NSSA border router. This allows for limited redistribution into the stub area.

Totally NSSA: A totally NSSA is similar to an NSSA, but it also does not accept summary LSAs. This means that routers in a totally NSSA only know about networks within their area, the redistributed routes, and a default route to the rest of the network.

In a real-world scenario, consider a large enterprise with multiple branches. The head office could be configured as area 0 (the OSPF backbone), and each branch could be a separate area. If a branch only needs to communicate with the head office and not with other branches, it could be configured as a stub or totally stub area to reduce routing traffic and simplify management. If a branch needs to redistribute routes from another routing protocol, it could be configured as an NSSA or totally NSSA.

Remember, the choice of area type depends on the specific requirements of your network and business needs. It's all about finding the right balance between network performance, administrative control, and resource utilization. Hope this helps! 

Lab and Script file: https://drive.google.com/file/d/1h-NiHT--MiPSPZ2joBqB1OleodzmEEN1/view?usp=sharing

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