From the user's point of view, domain names are useful as arguments to a local agent, called a resolver, which retrieves information associated with the domain name. Thus a user might ask for the host address or mail information associated with a particular domain name. To enable the user to request a particular type of information, an appropriate query type is passed to the resolver with the domain name.
From the resolver's point of view, the database that makes up the domain space is distributed among various name servers. Different parts of the domain space are stored in different name servers, although a particular data item will be stored redundantly in two or more name servers. The resolver starts with knowledge of at least one name server. When the resolver processes a user query it asks a known name server for the information; in return, the resolver either receives the desired information or a referral to another name server. Using these referrals, resolvers learn the identities and contents of other name servers. Resolvers are responsible for dealing with the distribution of the domain space and dealing with the effects of name server failure by consulting redundant databases in other servers.
Name servers manage two kinds of data. The first kind of data held in sets called zones; each zone is the complete database for a particular "pruned" subtree of the domain space. The second kind of data is cached data which was acquired by a local resolver.
A host can participate in the domain name system in a number of ways, the simplest is shown below:
Local Host | Foreign
|
+---------+ +----------+ | +--------+
| | user queries | |queries | | |
| User |-------------->| |---------|->|Foreign |
| Program | | Resolver | | | Name |
| |<--------------| |<--------|--| Server |
| | user responses| |responses| | |
+---------+ +----------+ | +--------+
| A |
cache additions | | references |
V | |
+----------+ |
| cache | |
+----------+ |
A name server could be a stand alone program on a dedicated machine or a process or processes on a large timeshared host. A simple configuration might be:
The DNS requires that all zones be redundantly supported by more than one name server. Designated secondary servers can acquire zones and check for updates from the primary server using the zone transfer protocol of the DNS. This configuration is shown below:
The labels must follow the rules for ARPANET host names. They must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphen. Note that while upper and lower case letters are allowed in domain names, no significance is attached to the case.
Various objects and parameters in the DNS have size limits. They are listed below:
From the user's point of view, domain names are useful as arguments to a local agent, called a resolver, which retrieves information associated with the domain name. Thus a user might ask for the host address or mail information associated with a particular domain name. To enable the user to request a particular type of information, an appropriate query type is passed to the resolver with the domain name.
From the resolver's point of view, the database that makes up the domain space is distributed among various name servers. Different parts of the domain space are stored in different name servers, although a particular data item will be stored redundantly in two or more name servers. The resolver starts with knowledge of at least one name server. When the resolver processes a user query it asks a known name server for the information; in return, the resolver either receives the desired information or a referral to another name server. Using these referrals, resolvers learn the identities and contents of other name servers. Resolvers are responsible for dealing with the distribution of the domain space and dealing with the effects of name server failure by consulting redundant databases in other servers.
Name servers manage two kinds of data. The first kind of data held in sets called zones; each zone is the complete database for a particular "pruned" subtree of the domain space. The second kind of data is cached data which was acquired by a local resolver.
A host can participate in the domain name system in a number of ways, the simplest is shown below:
A name server could be a stand alone program on a dedicated machine or a process or processes on a large timeshared host. A simple configuration might be:
The DNS requires that all zones be redundantly supported by more than one name server. Designated secondary servers can acquire zones and check for updates from the primary server using the zone transfer protocol of the DNS. This configuration is shown below:
Conventions
The DNS specifications attempt to be as general as possible in the rules for constructing domain names.
The labels must follow the rules for ARPANET host names. They must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphen. Note that while upper and lower case letters are allowed in domain names, no significance is attached to the case.
Various objects and parameters in the DNS have size limits. They are listed below:
Ref
RFC 1035: DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION