Description: NSSA (Not So Stubby Area) is a type of area in the OSPF (Open Shortest Path First) routing protocol that allows the inclusion of external routes while maintaining certain characteristics of a stub area. In OSPF, areas are used to segment a network and optimize routing, and stub areas are those that do not allow the propagation of external routes, which helps reduce complexity and the size of routing tables. However, NSSA was designed to overcome this limitation, allowing external routes to be imported and distributed within the network, but with restrictions that prevent the propagation of external routes to other areas. This means that an NSSA can receive routing information from external sources, such as routes from other routing protocols, while still acting as a stub area for the rest of the OSPF network. This feature is particularly useful in environments where integration of different routing systems is required without compromising the efficiency and simplicity of network design. In summary, NSSA provides a balance between the flexibility of receiving external routes and the efficiency of maintaining a more controlled routing structure.
History: NSSA was introduced in the OSPFv2 specification in 1998 as part of RFC 1587, which defined stub areas and their behavior. The need for NSSA arose from the increasing complexity of networks and the need to integrate different routing protocols without losing the advantages of stub areas. As networks evolved, it became clear that a more flexible approach was needed to allow interoperability between different routing systems.
Uses: NSSA is primarily used in network environments where integration of different routing protocols is required, such as in enterprise networks that combine OSPF with BGP or EIGRP. It allows organizations to maintain the efficiency of OSPF while connecting to external networks that use other protocols. It is also useful in situations where there is a need to limit the propagation of external routes to other areas within the OSPF network.
Examples: An example of NSSA usage could be a company that has an internal OSPF network and needs to connect to an Internet service provider using BGP. By configuring an NSSA, the company can receive external routes from BGP without compromising the routing structure of its OSPF network. Another case could be a network that uses OSPF for internal communication and EIGRP for connection to a branch, where NSSA allows interoperability without complicating the configuration.
