.: Advanced Linux Networking :.

TCP/IP is the most popular network stack. The Internet is built upon TCP/IP, and the stack supports the most popular network protocols, including most of those discussed in this book. In most cases, you can't simply unlink a network application from one stack and tie it to another stack, although a few applications do support multiple network stacks. Part of the reason for TCP/IP's popularity is its flexibility. TCP/IP is a routable network stack, meaning that a computer with multiple network interfaces can partially process TCP/IP packets and pass those packets from one network to another. TCP/IP routing is flexible and allows for routing based on decentralized network maps; there's no need for a centralized database for network routing to occur. Furthermore, TCP/IP supports a large network address (32 bits, with 128-bit addresses coming with IPv6, as described in Chapter 2) and a hierarchical naming structure. All these features make TCP/IP well suited to function as a network stack for a globe-spanning network.

On an individual Linux computer, TCP/IP is a good choice because of its support for so many important network protocols. Although many non-Unix platforms developed proprietary protocol stacks in the 1980s, Unix systems helped pioneer TCP/IP, and most Unix network protocols use TCP/IP. Linux has inherited these protocols, and so a Linux-only or Linux/Unix network operates quite well using TCP/IP alone; chances are you won't need to use any other network stack in such an environment.

Common protocols supported by TCP/IP include HTTP, FTP, the Simple Mail Transfer Protocol (SMTP), the Network File System (NFS), Telnet, Secure Shell (SSH), the Network News Transfer Protocol (NNTP), the X Window System, and many others. Because of TCP/IP's popularity, tools that were originally written for other network stacks can also often use TCP/IP. In particular, the Server Message Block (SMB)/Common Internet File System (CIFS) file-sharing protocols used by Windows can link to TCP/IP via the Network Basic Input/Output System (NetBIOS), rather than tying to the NetBIOS Extended User Interface (NetBEUI), which is the native DOS and Windows protocol stack. (All versions of Windows since Windows 95 also support TCP/IP.) Similarly, Apple's file-sharing protocols now operate over TCP/IP as well as over AppleTalk.

Although it's very popular and can fill many network tasks, TCP/IP isn't completely adequate for all networking roles. For instance, your network might contain some systems that continue to use old OSs that don't fully support TCP/IP. An old Macintosh might only support file sharing over AppleTalk, for instance, or you might have DOS or Windows systems configured to use IPX or NetBEUI. In these situations, Linux's support for alternative network stacks can be a great boon.