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CCNP Routing and Switching ROUTE 300-101: Official Cert Guide by Kevin Wallace

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External Routes in NSSAs

Routes can be redistributed into OSPF on any OSPF router, with a few exceptions. The router can be internal to area 0, like Router RD1 in the many examples earlier in this chapter. It can also be an ABR connected to several areas. It can be a router internal to a nonbackbone area as well.

Of the four types of stubby areas, two do not allow redistribution into the area, and two do allow redistribution—even though none of the stubby area types allow Type 5 LSAs. OSPF does not allow routers in stubby and totally stubby areas to inject external routes. However, routers in not-so-stubby areas—NSSAs—can redistribute routes, while still holding to the restriction of having no Type 5 LSAs.

OSPF supports the injection of external ...

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