Domain Name System (DNS)

Domain Registration

Website Hosting

Asif Shahzad, Assistant Professor of Computer ScienceCOMSATS, Lahore. asifsh7@gmail.com

http://bitspedia.com

Understanding DNS

• Maps domain and sub-domains to hosts

• In start, it was a simple text file maintained by the Network Information Center that mapped names to IP addresses

• University of Wisconsin developed DNS, a distributed database for managing domain name and IP addresses, in 1983.

• As the number of computers or devices increased, the system was transferred to hierarchical structure.

Understanding DNS

• ICANN is responsible for managing and coordinating the DNS to ensure universal resolvability

• Caching Name Server: Receives requests for domains and responds IP address of the domain or list of authoritative DNS servers which it has cached when serving earlier users’ requests

• Authoritative Name Server: Either it has host IP address of the domain being queried or list of other authoritative servers

Understanding DNS

Understanding DNS structure

• The heart of the DNS are, 13 Root Servers, distributed around the world. (Actually it’s a network of hundreds of servers, using anycast approach)

• All 13 contain the same vital information

• The root name servers publish the root zone file to other DNS servers and clients on the Internet. The root zone file describes where the authoritative servers for the DNS top-level domains (TLD) are located; in other words: which server one has to ask for names ending in one of 267 (September 2007) TLDs, such as ORG, NET, NL or AU. See: http://www.iana.org/domains/root/db

DNS Root Servers

DNS “Time To Live”

• TTL controls how long a IP-Host entry can remain in the DNS server. Its cache timeout.

• If you change a DNS record, resolvers would continue to resolve original address until the TTL expires. So its better to set short TTL in start.

• Wait TTL to expire, before expecting the DNS records to be fully propagated.

Domain Name Registry and Registrar

• A Domain Name Registry is a database of all domain names and the associated name servers and registrant information in the top level domains (TLDs). TLD Registries are operated by multiple companies, some companies operate more than one TLD Registry.

• A Domain Name Registrar is an organization or commercial entity that manages the reservation of Internet domain names. These are accredited by ICANN or ccTLD Registry operators.

Extensible Provisioning Protocol (EPP)

• The Extensible Provisioning Protocol (EPP) is a flexible protocol designed for allocating objects within registries over the Internet.

• The motivation for the creation of EPP was to create a robust and flexible protocol that could provide communication between domain name registries and domain name registrars.

Types of Hosting Servers

• Shared Hosting Server– Shared between multiple users. No freedom to install new softwares,

or update/stop/restart servers

• Virtual Server Hosting Server– Its dedicated to each user. User operate it just as it’s a dedicated

computer allocated to him but its all virtual– On single physical computer, multiple OS are setup, and each OS

instance is assigned to particular user. Some intermediate virtualization software are used e.g. Xen, etc.

– If you choose VPS, I recommend Linode.com. Its best company, I am using it for last 4 years almost. They have blazing fast servers and awesome response time whenever you need to contact support.

• Dedicated Server Hosting Server– A dedicated server (hardware) is allocated to user. Its cost is higher

than others. But these are more fast and you get full freedom.

Hosting Server

• So when a user makes a request for a domain the host-IP address is returned to the browser by the nearest DNS server cache

• Then browser sends the web request to received IP address. The web server must be running on your configured host. DEMO

Registering a Domain Name

• Select a Domain Registrar

• Check domain availability, register it providing domain owner details

• Configure Name Server for your domain that contains the host details for the domain or sub-domains

• See the Name Server of some website using whois query. DEMO

Whois Protocol

• A text based protocol used to query information about a domain from the Domain Registrar. This information usual contains:

– When the domain was registered

– When it was updated

– When the domain registration would expire

– What are the domain registrant details

– What are the authoritative Name Servers of domain

• Read Whois RFCs for further details

Host Your Website

• Choose a hosting provider. You would get the IP address host computer

• Open DNS server settings that you used while registering the domain

• Map your domain and sub-domains to different hosts (IP Addresses) in DNS Server

• Lets see an already configured domain and its Name Server settings, see DEMO

Virtual Host

• Do you want your web server to serve only a single domain? Definitely not.

• “Virtual hosting is a method for hosting multiple domains on a single server (or pool of servers).

• A web server is configured to serve different domains.

• How your server knows which domain was requested? The “Host” header contains requested domain name. Demo or see next slide.

Web Server Configuration

• After you registered domain, setup the Name Server and configured the Name Server with hosts address for the domain or sub-domains

• Now its time to tell your web-server to respond web requests for a particular domain. As a web server may host one or more domain contents. DEMO