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The Corporate InternetWhile online services and protocol gateways have their place, it is becoming increasingly common for companies to base their internal networks on TCP/IP. As noted earlier, virtually every computer operating system from DOS on PCs to MVS on mainframes is capable of communicating over TCP/IP. By designing your corporate network around TCP/IP, you not only gain the flexibility of an open, standards-based communication system, but you also greatly simplify the process of interfacing your private network with the Internet.Since TCP/IP is both open and pervasive, it doesn't matter what underlying network hardware technology you choose. You can run TCP/IP over Ethernet, Token-Ring, FDDI, serial lines or any other network access topology. In fact, most large corporate networks include a variety of these technologies and TCP/IP can be the glue that holds them together. AddressingIn designing a TCP/IP-based network, one of your fundamental concerns will be addressing. Unlike protocols such as IPX, which derives its network addresses dynamically, usually by reading the MAC-layer address of the network interface card (NIC), TCP/IP addresses must be assigned to devices on your network. A TCP/IP address is a 32-bit entity made up of a network address and a node address, usually represented in dotted-decimal notation. Although it is fairly common to divide this address space evenly with 16 bits for the network address and 16 bits for the node address, this may vary depending on the number of computers connected to your network.
Since all computers attached to the Internet must have unique addresses,
some entity must assume responsibility for assigning these addresses. These
responsibilities are currently handled by the Internet Network Information
Center, or InterNIC (www.internic.net; (800) 444-4345), which is managed
by Network Solutions, Inc., Herndon, Va. Addresses are divided into classes
depending on the number of nodes on your network. For example, a Class C
Internet address provides enough addresses for up to 255 computer systems.
A Class B address provides enough addresses for more than 65,000 computers.
Although InterNIC controls the allocation of official Internet addresses,
you can build a corporate network around TCP/IP using any set of addresses
you choose, as long as you don't want to connect to the Internet. However,
the InterNIC recommends that such private networks utilize the address space
reserved for this purpose as detailed in the Internet's Request for Comments
document number 1597. Many companies have learned the hard way that it is
better to secure official address space before building your internal IP
network, even if you do not plan to connect to the Internet immediately.
For many organizations, securing address space will be handled by the ISP,
but if you choose t
his approach, you should insist on ownership of the address
space to protect yourself in case you decide to change service providers
at a later date.
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