The Tcpip Suite

Critical Skills

10.1 Uncover the General Seven-Layer OSI Network Model

10.2 Discover the TCP/IP Protocol Architecture

10.3 Learn About the Address Resolution Protocol

As a system administrator, you will be required to handle problems that may affect one or more networked UNIX systems or involve network services at a lower level where protocol operation knowledge is necessary. As a result, direct interaction with TCP/IP and related services might be needed. Therefore, you will need a good understanding of TCP/IP, associated protocols, and applications. Today, many corporations, institutions, and other organizations use TCP/IP extensively and universally to address all aspects of network connectivity in a multi-vendor environment. It is the protocol family of choice with networking manufacturers, operating system vendors, and users alike. In fact, the world's largest network, the Internet, uses TCP/IP exclusively. UNIX was the first popular operating system to use TCP/IP, and TCP/IP continues to be the most widely used set of networking protocols for this and other operating systems.

If you have accessed the Web using a browser, transferred files using FTP, accessed a remote NFS file system, or sent email via the Internet, you have indirectly used TCP/IP. Fundamentally, TCP/IP provides a standard way to deliver information from one system to another without concern for operating system differences and network hardware characteristics. TCP/IP is an acronym that stands for two separate protocols: Transmission Control Protocol (TCP) and Internet Protocol (IP). However, TCP/IP generally refers to these protocols, plus a suite of related protocols and services. For example, the File Transfer Protocol (FTP) uses TCP/IP and provides a basic file transfer facility between a pair of systems. If the system supports TCP/IP, it is generally assumed to support FTP and a host of other protocols and services as well.

Today, the TCP/IP suite is supported on every major computer operating system available. For example, it is supported on HP-UX, Solaris, Linux, AIX, and many more. As such, it is considered the most popular networking protocol, and many of the same TCP/IP services are available on different versions of UNIX. This is good news, because many of the core functions of TCP/IP and applications are the same across different versions of UNIX. The operations of TCP/IP are independent of operating system or computer platform. The protocols hide the underlying operating system details and provides a common framework for establishing connectivity among systems. For instance, an FTP client program is normally available across most implementations of TCP/IP, and a result of using this program, which implements the FTP protocol, is that data files may be transferred between dissimilar systems. In other words, a file may be copied from, say, a Windows machine to Solaris (or vice versa) without the need to worry about how the actual data of the file is stored with each operating system. The client and/or server processing the file automatically handles the file structure differences and adjusts accordingly.

The TCP/IP suite is built on industry standards and is documented quite completely in Request for Comments (RFCs) papers. These documents are widely available on the Internet from several Web sites, but the general authoritative source of such information can be obtained from http://www.ietf.org/ rfc.html. TCP/IP is defined within an open standards organization, which means that the protocols will remain open and common, and no single vendor can own the protocols or develop proprietary extensions.

TCP/IP is independent of any data link protocol and can be used with many different networking technologies, including FDDI, Ethernet, ATM, token ring, Frame Relay, and SMDS. TCP/IP makes it possible to build a truly heterogeneous network consisting of products and network technologies from many different vendors and sources. In fact, the Internet, which is considered the world's largest network, consists of devices from many networking vendors that operate together in a uniform fashion. That's not to say the Internet doesn't have its share of networking issues or problems, but, for the most part, many would agree that interoperability between equipment vendors isn't a major factor for the established core set of TCP/IP, protocols, and applications.

From a system administration point of view, many of the tools used to administer, monitor, and configure TCP/IP on systems are consistent across most UNIX operating system versions. However, one issue that can be a problem is that each UNIX operating system vendor can and does implement nonprotocol details differently. For example, the way IP address and hostname information is stored on each network device or UNIX systems is not covered by any RFC standard, nor should it be, since it is an implementation detail. Thus, for Solaris, the system name 10

is stored in a file called /etc/hostname.device, where device is the name of the default LAN interface. Other operating systems use different files or other mechanisms. The present TCP/IP suite provides a mechanism to dynamically assign IP addresses to devices, and it also mandates that they be uniquely assigned to each device attached to the network. However, IP addresses are stored on a local system and are not a protocol matter, but rather a network management or system configuration issue, which is traditionally resolved at the operating system level. Each operating system vendor provides its own solutions to how IP address information or other operating system parameters are to be stored. Since operating systems are completely nonstandardized between vendors, the name of the file or its location (or even the presence of a hostname file) varies between different operating systems and releases.

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