Note that even if a network attaches to a top-level structure of a
certain kind, the network itself can use a different technology. Just
as in the first main alternative described above, name resolution
needs to know about the top-level routing topology. However, because
that topology is very constrained, the top-level routing problem
can be handled by three simple steps: (1) a default path can
always be used to reach a top-level structure, (2) name resolution
needs to know which top-level structure a node is attached to and
(3) the top levels need to know how they are interconnected to
each other. Name resolution here also can result in a partial source
route or occur incrementally with late binding.