talking about setting up a network, usually people will much prefer to use DHCP server to automatically set TCP/IP setting on each computers, this way would save a lot of their time, rather than configure the computers one by one. the TCP/IP settings include ip address, subnet mask, default gateway, and DNS server. that was server based network, how about peer to peer? peer to peer dont have any servers, it means no DHCP. however, you need to manually configure it. and therefore, private ip addresses were there, reserved for private addressing. those ip addresses havent been assigned for computers on internet.
here they are :
Class A : 10.0.0.1 to 10.255.255.254
Class B : 172.16.0.1 to 172.31.255.254
Class C : 192.168.0.1 to 192.168.255.254