What is a DNS Lookup?

Before we answer the question of what a DNS Lookup is, we first need to know what DNS is and what it represents. DNS, which is an abbreviation for domain name system, is a kind of virtual DNS internet database, which translates domain names into IP addresses via DNS servers.

DNS Lookup is a technique that primarily, by sending a request to the DNS server, serves to find IP addresses at domain names as well as obtain all DNS records for the required domain names. When we talk about DNS lookup, then in the context of that, we should definitely mention 2 opposite techniques. The first is forward lookup and the second is reverse lookup.

What is Forward DNS?

With forward DNS, we look for the IP address that corresponds to a specific domain. For example if we take any domain, say BBC.com, then we will find using forward DNS that that domain correspond to the IPv4 151.101.128.81 and IPv6: 2a04:4e42:600::81

What is Reverse DNS?

Reverse DNS, as opposed to forward DNS, looks for a domain or host name that corresponds to the given IP address via the IP address self. Reverse DNS lookup for IPv4 addresses uses the in-addr.arpa domain. So for example reverse lookup for IPv4 9.9.9.9 will query 9.9.9.9.in-addr.arpa and give result dns9.quad9.net

When we talk about IPv6 addresses then they unlike IPv4 addresses use a special domain ip6.arpa. For example PTR record for Google IPv6 address 2607:f8b0:4009:816::200e in reverse resolution will be e.0.0.2.0.0.0.0.0.0.0.0.0.0.0.0.6.1.8.0.9.0.0.4.0. b.8.f.7.0.6.2.ip6.arpa

DNS Records Checker

As already mentioned, the primary function of DNS lookup is to obtain the IP address from the domain name via a query sent to the DNS server, but in addition to this, as a secondary task of the DNS checker, checking DNS records for the domain is also set. Accordingly, here you can get information about the following DNS records types:

  • A record - details about 32-bit IPv4 associated with the domain
  • AAAA record - details regarding the 128-bit IPv6 used by the host
  • PTR record - A pointer record which gives back the domain record name and is used for reverse DNS lookup
  • MX record - A mail exchanger used by the domain to send email
  • NS record - Authoritative NS - name servers
  • SOA record - specifies authoritative information including email from the administrator of the requested domain, serial number of the domain and a couple of other indicators
  • SPF record - It is an abbreviation for Sender Policy Framework which is a type of authentication that prevents fake email and that tells us that the email server is authorized to send email for a given domain.
  • DMARC record - It stands for Domain-based Message Authentication, Reporting and Conformance which is also an extra type of email protocol authentication and serves to protect an email domain from unauthorized use. With the DMARC record you show that the email is protected with SPF or DKIM and also what to do if these methods fail.

Check out the following examples DNS records for well-known domains with the most traffic such as Wikipedia, Youtube, Facebook, Amazon or Google.

For isolated specific tests for PTR, NS and MX where you can get extra information about the priority of mail servers and their IP addresses do not forget to check Reverse DNS, NS Lookup and especially MX Lookup.

  • IP Details
  • IP: 18.207.133.27
  • DNS Records
  • Reverse DNS - PTR Check
  • 27.133.207.18.in-addr.arpa
  • ec2-18-207-133-27.compute-1.amazonaws.com
  • NS - The Authoritative Nameservers: [ Class: - TTL: ]
  • u2.amazonaws.com (156.154.65.10)

    r1.amazonaws.com (205.251.192.27)

    r2.amazonaws.com (205.251.195.199)

    u1.amazonaws.com (156.154.64.10)

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