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TCP/IP stands for Transmission Control Protocol/Internet Protocol. While other networking protocols exist today (such as Novell's IPX, Apple's AppleTalk, etc.), TCP/IP has emerged a clear victor as the internetworking protocol. The latest version of TCP/IP is IPv6 though IPv4 stacks are almost universally used today.
[What is a protocol? Like in real life, a protocol is a minimal set of rules which participants from different backgrounds agree on to make formal contacts and to exchange information. In networking, a protocol usually means the same thing: it's a minimal set of commands which the computer industry agrees on so that diverse computers and application can communicate with each other. Examples of some of the formal "words" in the TCP/IP protocol are FIN, ACK, NACK, CLOSEWAIT, etc.]
TCP/IP is a higher level network transport protocol (higher than the ethernet protocol) which is designed to break up the information to be sent over the network into small, manageable chunks called packets. The protocol also provides for error checking and for retransmission of packets in case they are lost in transit.
The IP Number: Each host using TCP/IP has an IP number (also called IP address). The IP number is a 32-bit number usually written in the now familiar dotted decimal notation (for example 129.79.28.88 for host lnxed1). Each octet in the IP number is an eight bit number and thus ranges from 0 to 255 (decimal).
Reserved IP Numbers: On a given subnet, a number of IP number are reserved for special use. For example, 129.79.28.0 (i.e. the last octet is null) represents the network address for a subnetted network (more on subnetting later). 129.79.28.255 represents the IP broadcast address; a packet addressed to this IP number is received by every host on the subnet. In addition to these two, another IP number is usually assigned to a router or a gateway which connects the subnet to other subnets (for us, this number is 129.79.28.254). In other words, only 253 (out of 256) IP number are actually available for use as hostnames on a given subnet.
Finally, a few other special IP numbers should be mentioned. The address 127.0.0.1 is assigned to the loopback interface (implemented in software so that connections to the machine itself don't have to go out on the physical network) on your machine and the address 0.0.0.0 represents the entire network.
Further Study:
TCP/IP Sub-Protocols: There are a number of subprotocols under the TCP/IP umbrella. These include:
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