Host and Dns

Since name resolution is the part of a name system that is used most often, it is here that we must pay careful attention to implementation issues. The two most important ones are efficiency and reliability. Efficiency is essential due to the
many thousands or millions of resolutions performed every day on a large system; reliability is a consideration because users of the name system quickly come to rely on it and we must make sure it is robust.

The host table name system was the original mechanism used for implementing names on the early Internet. It consists simply of a set of tables containing mappings between names and addresses maintained on each machine in
the internetwork. When a name needs to be resolved the table is consulted to determine the appropriate address. This system is extremely simple, but not very capable, and not well- suited to a large global Internet, which is why it was eventually abandoned in favor of DNS.

Even though the host table name system is not the primary mechanism used for TCP/IP naming, it still used in two circumstances. The first is to implement a basic name system in a small local TCP/IP internetwork.The second is
as an adjunct to DNS, where it allows manual mappings to be created that override the DNS process when needed.

As a complete name system, DNS provides numerous capabilities that implement each of the three basic name system functions. The DNS name space is hierarchical and is organization using a multi-level structure with particular
naming rules. The DNS name registration system is based on the idea of a hierarchy of domains and registration authorities responsible for them. DNS name resolution is similarly hierarchical, and designed around interaction between name resolver and name server software components that consult databases of DNS resource records and communicate using a special messaging protocol to answer client queries.