Registration services for additional levels of heirarchy are described in a companion document. IANA is responsible for oversight of both operation and security of the DNS root. To this end, the number of 1LDNs registered at the root is deliber- ately kept within humanly managable limits. Only a few hundred root entries are anticipated. However, it is not anticipated that the root will be updated by multiple external registration authori- ties.
Technical considerations restrict the number of root servers.
The DNS UDP datagrams can support about 16 such servers. These servers are currently in the domain root-servers.net. Another technical consideration is the load placed on the servers. Operation of root servers is a voluntary service to the Internet com- munity. When there are more than enough volunteers, IANA will select sites that are well distributed topologically.