About 192.168.x.x addresses

I would like to know a few basic things about the IP addresses that begin with 192.168 tried to google about this, but couldn't find much.
Is this range of addresses used in all LANs and VPNs? Or is it used only when there are firewalls? Is the mask the same format (in the network of my company it is 255.255.255.0) in all LANs? The reason is that I would like to make a TCP/IP-based server for LANs that will only accept connections from the LAN computers, but want to generalize it to work in any LAN.
If someone could give me some hints or at least direct me to a source about the 192.168 range of IPs I would be very thankful.

192.168.0.0 - 192.168.255.255

Are what are known as RFC 1918 private IP addresses. They are actually 256 Class C addresses..

These addresses are 'private' IP addresses because they cannot travel on the Internet.. in other words, Internet routers will not route them.... thus they are used on internal networks.

Most companies use the 255.255.255.0 mask since it allows for 254 different hosts in that one subnet, which is pretty easy to work with..

Read the IP addressing sections of this site, and then hit the RFC
www.faqs.org/rfcs/rfc1918.html


Cheers,