Domain Name System
Domain Name SystemDNSahierarchicaldistributed naming system for
computers, services, or any resource connected to theInternetor
aprivate network.Is an essential component of the functionality of
mostInternetservices because it is the Internet's primarydirectory
service.Works as a directory lookup service which maps host names
(www.example.com) to IP addresses (192.168.xxx.xxx)Domain Name
space is a tree-structured name space consisting of root and branch
servers. It also defines the DNS protocol (part of Application
layer protocols) used for data communication in Domain name
system.
Why DNS?Preceding directory services were mostly text files
(hosts.txt).These directory text files were maintained manually and
made available by Stanford Research Institute for the ARPANET (
predecessor to the Internet). The hosts file contains lines of text
consisting of an IP address in the first text field followed by one
or more host names. It became difficult to maintain the hosts files
as networks and network nodes were added to the system with
increasing frequency. DNS was created in 1984 to answer the
shortfalls in previous directory services.
DNS ArchitectureDNS service is a distributed group effort. It
has a hierarchy to it.
Top level Domain name servers (.com, .org, etc.)Over 380 root
servers divided into 13 groups or root zones
For more info, visit
https://www.iana.org/domains/root/serversHow DNS works?DNS
recursive query mechanism is used in resolving the host names.
Below picture shows how the host name www.wikipedia.org
A network host is configured with an initial cache (so
calledhints) of the known addresses of the root name servers. Such
a hint file is updated periodically by an administrator from a
reliable source.A query to one of the root servers to find the
server authoritative for the top-level domain.A query to the
obtained TLD server for the address of a DNS server authoritative
for the second-level domain.Repetition of the previous step to
process each domain name label in sequence, until the final step
which returns the IP address of the host sought.
5DNS query mechanismsIn reality, our local computer sends a DNS
request to the DNS server. The DNS server acts as a client on our
behalf to get the IP address of the desired host name. The DNS
query-response process takes place in two ways: Iterative and
Recursive. In Iterative process, the DNS client asks each
server(root, top-level domain and authoritative name servers) to
get the IP address of a host name. In Recursive process, the DNS
client sends a query to one server and this server will collect
information from other low-level servers and send the response to
DNS client. Study tools & referencesWireshark : It is a free
and open source software used for network protocol analysis for
UNIX and Windows. Ipconfig : It is a command-line utility to know
about the network configuration of one computer, DHCP and DNS
settings. https://www.iana.org/domains: corporation that oversees
globalIP addressallocation,autonomous systemnumber allocation,root
zonemanagement in theDomain Name System(DNS),media types, and
otherInternet Protocol-related symbols and numbers.
