Computer Networks Primary, Secondary and Root Servers BY: RAHUL KELUSKAR (1741139) MEHAK GUPTA (1741134) SOURISH GHOSH(1741153)

Content Covered: DNS Name Spaces Distribution of Name Space Zone Root, Primary and Secondary Servers

Domain Name System To identify an entity, TCP/IP uses IP Addresses which uniquely identifies connection of host to internet 2. We Prefer to use names instead of numeric addresses. 3. Thus there is requirement for a system that can map addresses to names and vice versa..

Domain Name System When the internet was small , mapping was done using HOST FILE which was stored on each host. Host File had 2 columns name and address. DNS allows us to divide all information to be saved across varied location in smaller parts.

A user opens a web browser, enters www. example A user opens a web browser, enters www.example.com in the address bar, and presses Enter. The request for www.example.com is routed to a DNS resolver, which is typically managed by the user's Internet service provider (ISP), such as a cable Internet provider, a DSL broadband provider, or a corporate network. The DNS resolver for the ISP forwards the request for www.example.com to a DNS root name server. The DNS resolver for the ISP forwards the request for www.example.com again, this time to one of the TLD name servers for .com domains. The name server for .com domains responds to the request with the names of the four Amazon Route 53 name servers that are associated with the example.com domain. The DNS resolver for the ISP chooses an Amazon Route 53 name server and forwards the request for www.example.com to that name server. The Amazon Route 53 name server looks in the example.com hosted zone for the www.example.com record, gets the associated value, such as the IP address for a web server, 192.0.2.44, and returns the IP address to the DNS resolver. The DNS resolver for the ISP finally has the IP address that the user needs. The resolver returns that value to the web browser. The DNS resolver also caches (stores) the IP address for example.com for an amount of time that you specify so that it can respond more quickly the next time someone browses to example.com. For more information, see time to live (TTL). The web browser sends a request for www.example.com to the IP address that it got from the DNS resolver. This is where your content is, for example, a web server running on an Amazon EC2 instance or an Amazon S3 bucket that's configured as a website endpoint. The web server or other resource at 192.0.2.44 returns the web page for www.example.com to the web browser, and the web browser displays the page.

Namespace The process of mapping a unique name with the unique IP address. FLAT NAME SPACE – . A name is assigned to an address and name is a sequence of characters without structure. It can not be used in large system such as Internet. HIERARCHICAL NAME SPACE- Each name is made of several parts. The first part can define the nature of organization. Second part can define the name and third can define the departments in organization. For example Smart.pu.edu Smart.nitttr.edu smart.unix.com 

Distribution of NameSpace: ROOT SERVER-It is a server whose zone consist of whole tree. These servers are distributed all around the world. PRIMARY SERVER- A primary server loads all information from the local disk file. SECONDARY SERVER- It transfer the complete information from the primary server and it is called Zone transfer.

Zones: Domains are broken into zones for which individual DNS servers are responsible. Each name is made of several parts. What a server is responsible for or has authority over is called a zone The server makes a database called a zone file and keeps all the information for every node under that domain.

Root Server The root servers contain the information that makes up the root zone, which is the global list of top level domains. The root zone contains: •Generic top level domains – such as .com, .net, and .org •Country code top level domains – two-letter codes for each country, such as .se for Sweden or .no for Norway •Internationalized top level domains – generally equivalents of country code top level domain names written in the countries’ local character sets

Primary Domain Servers A primary DNS server is responsible for reading data related to the domain zone. The primary server is also responsible for communicating with the secondary server. It is responsible for creating, maintaining, and updating the zone file. The process of a primary web server communicating with the secondary server is known as a Zone Transfer, as zone data is being sent from a DNS server to another. If a primary server already contains the zone data for a domain, this data does not need to be replicated because the primary and secondary server continuously share zone data. 

Secondary Servers Serves as an addition to primary server Also referred to as ‘slave server’. Same features and capabilities as the primary server. Provides alternate source for services provided by primary server. Can be used for several services such as DNS server, application server etc. Does not have zone authority. gets zone file from another server possessing zone authority

Important Questions (Q) Describe the hierarchy of name servers. (6 Marks)

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