Domain name system (DNS)
DNS is used to resolve host name to their IP addresses by using a distributed database and a hierarchical naming system.
DNS systems assign a unique domain name for each of the IP’s generated making it easy for the web users instead of remembering numbers.
Over 200,000,000 domain names stored.
In the 1970’s before the concept of DNS came into existence, TCP/IP communications on the internet were made using a HOST.txt file which contained the information of all the hosts and their IP’s.
This text file was maintained by Stanford Research Institute (SRI) and was stored on a global FTP server. The problem with this approach was 1) As the number of hosts grew the text file became huge 2) Scalability 3) Confusions and collisions when the host file was not properly updated when new entries were made 4) Same host name resolving to multiple IP’s.
In 1984’s DNS was introduced which enabled having host names in a database that was replicated across multiple servers.
DNS was initially based on the RFC 882 (“Domain Names: Concepts and Facilities” ) and RFC 883 (Domain Names–Implementation and Specification) and was superseded by RFC 1034 (“Domain Names–Concepts and Facilities”) and RFC 1035 (“Domain Names–Implementation and Specification”)
DNS terminology and concepts
DNS Domain Name: DNS system is a hierarchical system where the domain names are stored in a distributed database containing host and domain names. All the names in a DNS database are arranged hierarchically in a tree like structure called the domain zone. Each branch of the tree represents a domain type.
A Domain Name is a sequence of labels from a node to the root separated by dots.
Name space has a maximum depth of 127 levels.
Domain names are limited to 255 characters and it identifies a node’s position in namespace.
Zones: Like domains are logical partitions of a DNS systems, zones are physical partitions within a DNS database. Information in a zone are stored in a Zone file. There is a one to one relationship between a zone and a domain.
Zone types and Zone transfer
Primary Zone: Original zone file where the domain entries can be modified, added or deleted.
Secondary Zone: This is the copy of the primary zone data which is read-only
Stub zone: It is a read only copy of the primary zone which contains information of domain resource.
Zone transfer: To prevent failure from hosting on just one zone server the information on the zone is replicated and synchronized to other host servers by zone transfer
The TLD’s are maintained by Name Registration Authority. Some of the popularly used TLD’s are:
Name servers store information regarding the name spaces in units called zones.
Types of Name server
· Authoritative Name Server- maintains the data
· Caching- stores data obtained from an authoritative server
Name Server Architecture
What is IP Address?
Computers that make up the internet are setup in large networks that communicate with each other with underground/underwater wires and are identified using strings of address known as IP Addresses.
IP addresses are unique addresses that are assigned to a host. These are 32 bits (4 bytes) long and consists of 2 components, network and host with each of the 4 bytes represented by numbers from 0 to 255 that are separated by dots.
How requests are handled by DNS?
DNS is used to translate actual name into IP Address.
When you type “www.xyz.com” in the web browser, workstation determines if the IP address is identified. It could be configured on your computer or your memory.
Operating system is configured to ask a resolving name server for IP address it doesn’t know. The resolving Name Server is configured manually or automatically within your OS.
The resolving Name Server may or mayn’t have this information in the memory or the cache.
It will ask the root Name server which provides the information related to the COM Name server called Top Level Domain(TLD) Name Server.
Resolving Name Server takes all this information from root Name server and saves it in the cache.
When Resolving Name Server queries COM TLD name server it redirects to the corresponding authoritative name server with the help of domain registrars.
Resolving name server again queries the authoritative name server and saves the IP address in cache.
It responds to the Operating system with the website’s IP Address.