Specifications

9033691-01 VH-2402-L3 Management Guide 159
Mapping Domain Names to Addresses
Name-to-address translation is performed by a program
called a Name server. The client program is called a Name
resolver. A Name resolver may need to contact several
Name servers to translate a name to an address.
The Domain Name System (DNS) servers are organized in a
somewhat hierarchical fashion. A single server often holds
names for a single network, which is connected to a root
DNS server – usually maintained by an ISP.
Domain Name Resolution
The domain name system can be used by contacting the
name servers one at a time, or by asking the domain name
system to do the complete name translation. The client
makes a query containing the name, the type of answer
required, and a code specifying whether the domain name
system should do the entire name translation, or simply
return the address of the next DNS server if the server
receiving the query cannot resolve the name.
When a DNS server receives a query, it checks to see if the
name is in its subdomain. If it is, the server translates the
name and appends the answer to the query, and sends it
back to the client. If the DNS server cannot translate the
name, it determines what type of name resolution the client
requested. A complete translation is called recursive
resolution and requires the server to contact other DNS
servers until the name is resolved. Iterative resolution
specifies that if the DNS server cannot supply an answer, it
returns the address of the next DNS server the client should
contact.
Each client must be able to contact at least one DNS server,
and each DNS server must be able to contact at least one
root server.
The address of the machine that supplies domain name
service is often supplied by a DCHP or BOOTP server, or
can be entered manually and configured into the operating
system at startup.