5.4 Stub and Totally Stubby Areas
5.4.2 Stub and totally stubby area criteria
An area can be qualified as a stub or totally stubby when it meets the following criteria:
  • There is a single exit point from that area.
  • The area is not needed as a transit area for virtual links. (Virtual links are discussed at the end of this chapter.)
  • No ASBR is internal to the stub area.
  • The area is not the backbone area (Area 0).

These criteria are important because a stub/totally stubby area is configured primarily to exclude external routes. If these criteria are not met, external links may be injected into the area, invalidating their stubby nature.