NOT SO STUBBY AREAS (NSSAS)
OSPF also supports the idea of not so stubby areas (NSSA), also shown in Figure 6-6. Areas are restricted in that they cannot receive AS external LSAs. Also, it might be desirable to allow a stubby area to pass advertising through its area, but not have to receive external LSAs from its default router. For example, in Figure 6-6, network 15 is attached to router 12, and router 12 is allowed to advertise about network 15, but need not be burdened with external advertising traffic, because router 11 provides this service.
Prior to NSSA it was not possible to run a remote site, such as network 15, to an OSPF border router, because routes from remote sites cannot be redistributed into a stub area. So, protocols like RIP ...
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