what is dns server

What is DNS server

Domain Name System (DNS) is a service that inbuilt in windows Server. The DNS has two types Zone first one is the forward lookup zone and the second one is the reverse lookup zone. forward lookup zone resolves host to IP address and reverses lookup zone resolve IP address to hostname.

A DNS name server is a server that stores the DNS records for a domain; a DNS name server responds with answers to queries against its database.

DNS working on 53 TCP/UDP port.

Types of DNS Records :

(Address Mapping record) The A-record It is used for Resolve domain names such as www.google.com into IP-addresses such as XXX.XXX.XXX.XXX.

(IP Version 6 Address record ) AAAA-Records An AAAA-record is used to specify for the IPv6 IP address for a host. It is equivalent to the A-record type for IPv4.

Canonical Name record (CNAME Record) is used for alias a hostname to another hostname. When a DNS client sends requests a record that contains a CNAME, which points to another hostname, in that case, the DNS resolution process is repeated with the new hostname.

Mail exchanger record (MX Record)—specified for the SMTP email server for the domain, it used to route outgoing emails to an email server.

Name Server records (NS Record)—specified for that a DNS Zone, such as google.com is delegated to a specific Authoritative Name Server and provides the IP address of the name server.

Reverse-lookup Pointer records (PTR Record) resolve the IP address to hostname.

Service Location (SRV Record)—a service location record, this is the MX but for other communication protocols.

Start of Authority (SOA Record) record can be store important information about the DNS such as the email address of the administrator, when the domain was last updated, and how long the server should wait between refreshes.

ALIAS-Records (Auto Resolved Alias) the ALIAS-records are virtual alias records resolved by Simple DNS Plus at the time of each request - providing synthesized records with data from a hidden source name.

Type of DNS Server

There are four categories in dns server

1.Recursive revolvers
2. Root name servers
3. TLD name-servers
4.Authoritative name servers. 


How recursive nameservers (DNS recursive) works?

A recursive resolver is the first stop in a DNS query. 

After receiving a DNS query from a web client, a recursive resolver will either respond with cached data, or send a request to a root nameserver.

After receiving a response from the authoritative nameserver containing the requested IP address, the recursive resolver then sends a response to the client.

During this process, the recursive resolver will cache information received from authoritative name servers.

 When a client requests the IP address of a domain name that was recently requested by another client, the resolver can circumvent the process of communicating with the nameservers, and just deliver the client the requested record from its cache.

What is Root nameserver?

The 13 DNS root nameservers are known to every recursive resolver.

A root server accepts a recursive resolver’s query which includes a domain name, and the root nameserver responds by directing the recursive resolver to a TLD nameserver, based on the extension of that domain (.com, .net, .org, etc.).

The root nameservers are overseen by a nonprofit called the Internet Corporation for Assigned Names and Numbers (ICANN).

As per IANA 13 root name servers 

List of Root Servers

a.root-servers.net198.41.0.4, 2001:503:ba3e::2:30Verisign, Inc.
b.root-servers.net199.9.14.201, 2001:500:200::bUniversity of Southern California,
Information Sciences Institute
c.root-servers.net192.33.4.12, 2001:500:2::cCogent Communications
d.root-servers.net199.7.91.13, 2001:500:2d::dUniversity of Maryland
e.root-servers.net192.203.230.10, 2001:500:a8::eNASA (Ames Research Center)
f.root-servers.net192.5.5.241, 2001:500:2f::fInternet Systems Consortium, Inc.
g.root-servers.net192.112.36.4, 2001:500:12::d0dUS Department of Defense (NIC)
h.root-servers.net198.97.190.53, 2001:500:1::53US Army (Research Lab)
i.root-servers.net192.36.148.17, 2001:7fe::53Netnod
j.root-servers.net192.58.128.30, 2001:503:c27::2:30Verisign, Inc.
k.root-servers.net193.0.14.129, 2001:7fd::1RIPE NCC
l.root-servers.net199.7.83.42, 2001:500:9f::42ICANN
m.root-servers.net202.12.27.33, 2001:dc3::35WIDE Project

What is a TLD nameserver?

A TLD nameserver maintains information for all the domain names that share a common domain extension, such as .com, .net, or whatever comes after the last dot in a URL. 

For example, a .com TLD nameserver contains information for every website that ends in ‘.com’. 

If a user was searching for google.com, after receiving a response from a root nameserver, the recursive resolver would then send a query to a .com TLD nameserver, which would respond by pointing to the authoritative nameserver (see below) for that domain.

  • Generic top-level domains: These are domains that are not country-specific, some of the best-known generic TLDs include .com, .org, .net, .edu, and .gov.
  • Country code top-level domains: These include any domains that are specific to a country or state. Examples include .uk, .us, .ru, and .jp

What is an authoritative nameserver?

An authoritative Nameserver is a DNS Server that holds the actual DNS records (A, CNAME, PTR, etc) for a particular domain/ address. 

A recursive resolver would be a DNS server that queries an authoritative nameserver to resolve a domain/ address.

The authoritative nameserver is usually the resolver’s last step in the journey for an IP address.

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