10-21-2015
DNS and hostname resolution
I've always been confused by technical discussions of DNS. They say that DNS is used to match a domain name with the IP address of a host on the Internet. The thing that confuses me is this premise that there is an exact, one-to-one correspondence between Internet domain names and hosts on the Internet. I find that to be a gross oversimplification. Like youtube.com is one computer. Is there really one computer for the domain www(.)youtube(.)com? I find that hard to believe. Considering that there are literally billions of videos on YouTube, I find it really hard to believe that all of them are stored on one computer. The same goes for things like Facebook. I seriously doubt that every single Facebook profile in the world is stored on a single server.
So I need someone to straighten this out for me. How does this work? What are these explanations of DNS leaving out of the picture? I'm sure domain names are, in fact, often distributed over multiple servers. It's possible these servers have the same IP address due to network address translation, so that might be an explanation. Also, do they have different hostnames that need to be resolved, and is this additional hostname resolution done with another directory service like NIS?
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LEARN ABOUT OSF1
res_init
res_init(3) Library Functions Manual res_init(3)
NAME
res_init - Searches for a default domain name and Internet address
LIBRARY
Standard C Library (libc.a, libc.so)
SYNOPSIS
#include <sys/types.h> #include <netinet/in.h> #include <arpa/nameser.h> #include <resolv.h>
void res_init ( void );
DESCRIPTION
The res_init() function reads the /etc/resolv.conf file for the default domain name and the Internet address of the initial hosts running
the name server, even if the name server is not functioning.
The res_init() function is one of a set of subroutines that form the resolver, a set of functions that resolve domain names. All resolver
functions use the /usr/include/resolv.h header file, which defines the _res data structure. The res_init() function stores domain name
information in the _res data structure.
NOTES
If the /etc/resolv.conf file does not exist, the res_init() function attempts name resolution using the local /etc/hosts file. If the sys-
tem is not using a domain name server, the /etc/resolv.conf file should not exist. The /etc/host file should be present on the system even
if the system is using a name server. In this instance, the file should contain the host IDs that the system requires to function even if
the name server is not functioning.
FILES
Contains the name server and domain name.
Contains hostnames and their addresses for hosts in a network. This file is used to resolve a hostname into an Internet address.
RELATED INFORMATION
Functions: dn_comp(3), dn_expand(3), dn_find(3), dn_skipname(3), _getlong(3), _getshort(3), putlong(3), putshort(3), res_mkquery(3),
res_query(3), res_search(3), res_send(3). delim off
res_init(3)