At the global top-level domain name (GTLD) level, the domain name system is essentially flat. There is little aggregation possible with the domain name space beyond that performed at the organization level. For example, most names of the form *.stanford.edu appear in the same part of the network, but stanford.edu is not aggregatable as part of an edu route. So, ``default-free'' content routers have to know essentially all second-level domain names.