hierarchical routing

The complex problem of routing on large networks can be

simplified by breaking a network into a hierarchy of smaller

networks, where each level is responsible for its own routing.

The Internet has, basically, three levels: the backbones, the

mid-levels, and the stub networks. The backbones know how to

route between the mid-levels, the mid-levels know how to route

between the sites, and each site (being an autonomous system)

knows how to route internally. See also Exterior Gateway

Protocol, Interior Gateway Protocol, transit network.