Summary

The TCP/IP protocol suite was developed so that cooperating computers can share resources across a network. Some TCP/IP suite protocols are used for transferring files between computers, sending mail, or determining who is logged in on another computer.

TCP is a connection-oriented protocol (acknowledgements sent by receiver to the originator), whereas UDP is a connectionless protocol (no acknowledgements are used).

The key to TCP/IP networking is found in the IP addressing, currently IPv4 (IP version 4). IPv4 addresses consist of a 32-bit number. When the Internet was commercially introduced it was broken down into smaller networks. Network classes were the mechanism that broke down the address space in line with these smaller networks.

Class A networks have network addresses from 1.0.0.0 through 127.0.0.0. The network number is the first octet, being from 1 to 127. That number uniquely identifies the class A destination network. The rest of the address, three octets, uniquely identifies a machine within that network.

Class B networks have addresses from 128.0.0.0 through 191.255.0.0. The network number is the first two octets, being from 128.0 through 191.255. The number uniquely identifies which class B network is the destination of the packet. The rest of the address uniquely identifies a machine on that network.

Class C networks have addresses from 192.0.0.0 through 223.255.255.0. The network number is the first three octets, being from 192.0.0 through 223.255.255. Each class C network can have one octet worth of hosts.

Class D networks have addresses from 224.0.0.0 to 239.255.255.255. Class D network addresses are used for multicast protocols.

Class E networks have addresses from 240.0.0.0 to 255.255.255.255. Class E networks are reserved for future use.