The hosts file is used for manual/static name resolution
for IP-based network clients.
It IS optional, and usually only used for very small
networks or for specific needs.
When a network machine needs to communicate with other
networked machines it must resolve the computer/resource
name (say
www.microsoft.com) to an IP address.
Hosts files provide this functionality by statically
mapping a computer name to an ip address in the form of <IP
ADDRESS> <SPACE> <RESOURCE NAME>
The default name resolution service on a machine will look
up the name in this file to get the corresponding IP address.
As you can imagine, having the entire internet worth of
domain names in a hosts file would be HUGE, and parsing it
would become very slow.Also if an IP address changes, all
those MANUAL hosts entries have to be updated.
Microsoft initially developed WINS (Windows Internet Naming
System) as a dynamically updating name resolution service
for Windows-based computers. They developed this in direct
competition to the existing X.500 standard utilized in the
UNIX world. (actually X.500 does much more)
The pitfall to WINS is it's incompatibility with
non-Windows machines. Also, it uses RPC by default, which
is not routed across most routers as it was intended as a
LAN/single-segment solution.
Fast forward from 1988 to 1998 and we find MS delivering a
Better, Faster, Stronger Name Resolution Service in the
form of Dynamic Domain Name Service (DDNS). DDNS is mostly
MS's name for their implementation of the X.500 standard.
Make sense? Please reply to newsgroup for clarification.