What distinguishes an intranet from any other kind of private network is that it is based on TCP/IP-the same protocols that apply to the Internet. TCP/IP refers to two protocols that work together to deliver data: the Transmission Control Protocol (TCP) and the Internet Protocol (IP). When you send information across an intranet, the data is broken into small packets. The packets are sent independently through a series of switches called routers. Once all the packets arrive at their destination, they are recombined into their original form. The Transmission Control Protocol breaks the data into packets and recombines them on the receiving end. The Internet Protocol handles the routing of the data and makes sure it gets sent to the proper destination.

1. In some companies, there may be a mix of TCP/IP-based intranets and networks based on other networking technology, such as NetWare. In that instance, the TCP/IP technology of an intranet can be used to send data between NetWare or other networks, using a technique called IP tunneling. In this instance, we'll look at data being sent from one NetWare network to another, via an intranet. NetWare networks use the IPX (Internet Packet Exchange) protocol as a way to deliver data-and TCP/IP networks can't recognize that protocol. To get around this, when an IPX packet is to be sent across an intranet, it is first encapsulated inside an IP packet by a NetWare server specifically for and dedicated to providing the IP transport mechanism for IPX packets.
2. Data sent within an intranet must be broken up into packets of less than 1,500 characters each. TCP breaks the data into packets. As it creates each packet, it calculates and adds a checksum to the packet. The checksum is based on the byte values, that is, the precise amount of data in the packet.
3. Each packet, along with the checksum, is put into separate IP wrappers or "envelopes." These wrappers contain information that details exactly where on the intranet-or the Internet-the data is to be sent. All of the wrappers for a given piece of data have the same addressing information so that they can all be sent to the same location for reassembly.
4. The packets travel between networks by intranet routers. Routers examine all IP wrappers and look at their addresses. These routers determine the most efficient path for sending each packet to its final destination. Since the traffic load on an intranet often changes, the packets may be sent along different routes, and the packets may arrive out of order. If the router sees the address is one located inside the intranet, the packet may be sent directly to its destination, or it may instead be sent to another router. If the address is located out on the Internet, it will be sent to another router so it can be sent across the Internet.
5. As the packets arrive at their destination, TCP calculates a checksum for each packet. It then compares this checksum with the checksum that has been sent in the packet. If the checksums don't match, TCP knows that the data in the packet has been corrupted during transmission. It then discards the packet and asks that the original packet be retransmitted.
6. TCP includes the ability to check packets and to determine that all the packets have been received. When all the non-corrupt packets are received, TCP assembles them into their original, unified form. The header information of the packets relays the sequence of how to reassemble the packets.
7. An intranet treats the IP packet as it would any other, and routes the packet to the receiving NetWare network. On the receiving NetWare network, a NetWare TCP/IP server decapsulates the IP packet-it discards the IP packet, and reads the original IPX packet. It can now use the IPX protocol to deliver the data to the proper destination.