To ensure that a low-end router never becomes a DR, it can be set to priority 0. If a router
interface is set with a priority of 0, that router is ineligible to become the DR for that network.
If all routers on a segment are set to 0, OSPF does not function on that segment.
all external routes (Type 5 LSAs). For areas that are connected to the backbone by only one
ABR (that is, the area has one exit point), there is no need to maintain information about
external routes. Stub areas are similar to regular areas, except that the routers do not enter
external routes in the area's databases.
when there is a single exit point from the area or when the choice of exit point need not be made
on a per-external-destination basis. You might need to specify a stub area with no default cost
if the area has more than one exit point.
area default cost is advertised to all routers within the stub area by a border router and is used
for all external destinations.