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For example, to do a reverse lookup of the IP address 8.8.4.4 the PTR record for the domain name 4.4.8.8.in-addr.arpa would be looked up, and found to point to dns.google. If the A record for dns.google in turn pointed back to 8.8.4.4 then it would be said to be forward-confirmed.
Each / 8 block contains 256 3 = 2 24 = 16,777,216 addresses, which covers the whole range of the last three delimited segments of an IP address. This means that 256 /8 address blocks fit into the entire IPv4 space.
Google Public DNS is a Domain Name System (DNS) service offered to Internet users worldwide by Google. It functions as a recursive name server . Google Public DNS was announced on December 3, 2009, [ 1 ] in an effort described as "making the web faster and more secure."
Returns all records of all types known to the name server. If the name server does not have any information on the name, the request will be forwarded on. The records returned may not be complete. For example, if there is both an A and an MX for a name, but the name server has only the A record cached, only the A record will be returned.
A reverse DNS lookup is a query of the DNS for domain names when the IP address is known. Multiple domain names may be associated with an IP address. The DNS stores IP addresses in the form of domain names as specially formatted names in pointer (PTR) records within the infrastructure top-level domain arpa. For IPv4, the domain is in-addr.arpa.
A public recursive name server (also called public DNS resolver) is a name server service that networked computers may use to query the Domain Name System (DNS), the decentralized Internet naming system, in place of (or in addition to) name servers operated by the local Internet service provider (ISP) to which the devices are connected.
The DNS server also features blocking domain names using block lists [23] and also supports using HTTP or SOCKS5, for transport of DNS requests over Tor network. [24] The DNS server supports running independently developed plugins that can be used to process and respond to DNS requests.
nslookup is a member of the BIND name server software. Andrew Cherenson created nslookup as a class project at UC Berkeley in 1986 and it first shipped in 4.3-Tahoe BSD [1] In the development of BIND 9, the Internet Systems Consortium planned to deprecate nslookup in favor of host and dig.