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Full Discussion: DNS and hostname resolution
Special Forums IP Networking DNS and hostname resolution Post 302962621 by mr_zeratul on Wednesday 16th of December 2015 02:06:11 PM
Old 12-16-2015
You can approach it from various angles:
a) 1-to-1 mapping is not strictly correct. It can be as many as you want to point your domains to a specific IP. For example, I have this public IP 8x.73.1.9 (all made up, course). And I registered 3 domains: mydomain.com, myotherdomain.net, mythirdsite.org. I can have them all pointed to the same IP. Assuming that I have setup web servers (or mail servers) to each and one of them, they can serve contents distincts from one another while sharing the same IP and users won't even notice that they are connected to 1 IP.

b) With regards to big companies, the IPs that you are connecting to are the ones closest to your location. So 2 people (who are geographical separated) both connecting to youtube.com are actually connecting to different IPs. That is made possible by CDNs, DNS etc. I think IPv6 has inherent support for it via anycast.

c) IPs used by big co's are mostly virtual. Meaning they are not actually tied to a single machine but rather to a group of machine. That provides huge bandwith, failover, loadbalancing etc.

Sorry for my English, I tried my best.

Last edited by mr_zeratul; 12-16-2015 at 03:07 PM.. Reason: typo
 

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Net::DNS::Resolver::Recurse(3)				User Contributed Perl Documentation			    Net::DNS::Resolver::Recurse(3)

NAME
Net::DNS::Resolver::Recurse - Perform recursive dns lookups SYNOPSIS
use Net::DNS::Resolver::Recurse; my $res = Net::DNS::Resolver::Recurse->new; DESCRIPTION
This module is a sub class of Net::DNS::Resolver. So the methods for Net::DNS::Resolver still work for this module as well. There are just a couple methods added: hints Initialize the hint servers. Recursive queries need a starting name server to work off of. This method takes a list of IP addresses to use as the starting servers. These name servers should be authoritative for the root (.) zone. $res->hints(@ips); If no hints are passed, the default nameserver is asked for the hints. Normally these IPs can be obtained from the following location: ftp://ftp.internic.net/domain/named.root recursion_callback This method is takes a code reference, which is then invoked each time a packet is received during the recursive lookup. For example to emulate dig's "+trace" function: $res->recursion_callback(sub { my $packet = shift; $_->print for $packet->additional; printf(";; Received %d bytes from %s ", $packet->answersize, $packet->answerfrom ); }); query_dorecursion This method is much like the normal query() method except it disables the recurse flag in the packet and explicitly performs the recursion. $packet = $res->query_dorecursion( "www.netscape.com.", "A"); IPv6 transport If the appropriate IPv6 libraries are installed the recursive resolver will randomly choose between IPv6 and IPv4 addresses of the nameservers it encounters during recursion. If you want to force IPv4 transport use the force_v4() method. Also see the IPv6 transport notes in the Net::DNS::Resolver documentation. AUTHOR
Rob Brown, bbb@cpan.org SEE ALSO
Net::DNS::Resolver, COPYRIGHT
Copyright (c) 2002, Rob Brown. All rights reserved. Portions Copyright (c) 2005, Olaf M Kolkman. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. $Id: Recurse.pm 932 2011-10-26 12:40:48Z willem $ perl v5.16.2 2012-01-27 Net::DNS::Resolver::Recurse(3)
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