The TCP/IP (Transmission Control Protocol/Internet Protocol) suite, included with the SCO OpenServer Desktop and Enterprise systems, provides the basis for many useful services, including electronic mail, file transfer, remote login, network monitoring, and others, described in ``Administering TCP/IP''.
TCP/IP is a set of protocols and programs used to interconnect computer networks and to route traffic among different types of computers. These protocols describe allowable data formats, error handling, message passing, and communication standards. Computer systems that use TCP/IP speak a common language, regardless of hardware or operating system differences.
Many large networks conform to these protocols, including the Internet. Thousands of computers at universities, government agencies, and corporations are connected to a network that follows the TCP/IP protocols. Any machine on the Internet can communicate with any other. Machines on the Internet are referred to as hosts or nodes and are defined by their Internet (or IP) address.
TCP/IP is made up of three basic protocols -- Internet Protocol (IP), Transmission Control Protocol (TCP), and User Datagram Protocol (UDP) -- as well as a variety of others that run over the IP protocol stack.
The Internet Protocol defines a data delivery system wherein the sending and receiving machines are not necessarily directly connected. IP splits data into packets of a given size, which are then forwarded to the receiving machine via the network. These individual packets of data (often called ``datagrams'') are routed through different machines on the Internet to the destination network and receiving machine. A particular set of data, such as a file, can be broken up into several datagrams that are sent separately.
A datagram consists of header information and a data segment. The header contains information about routing and processing the datagram. Datagrams can be further fragmented into smaller pieces, depending on the physical requirements of the networks they cross. For example, when a gateway sends a datagram to a network that cannot accommodate the datagram as a single packet, the datagram must be split into pieces that are small enough for transmission. The datagram fragment headers contain the information necessary to reassemble the fragments into the complete datagram. Fragments do not necessarily arrive in order; the software module implementing the IP protocol on the destination machine must reassemble the fragments into the original datagram. If any fragments are lost, the entire datagram is discarded.
The Transmission Control Protocol works with IP to provide reliable delivery. It provides a means to ensure that the various datagrams making up a message are reassembled in the correct order at their final destination and that any missing datagrams are re-sent until they are correctly received.
The primary purpose of TCP is to avoid the loss, damage, duplication, delay, or misordering of packets that can occur under IP. When IP forwards datagrams, individual datagrams may or may not arrive, and they probably will not arrive in the order in which they were sent. TCP adds the reliability that IP lacks. Also, security provisions such as limiting user access to certain machines can be implemented through TCP.
TCP provides reliability by using checksums (error detection codes) on the data, sequence numbers in the TCP header, positive acknowledgment of data received, and retransmission of unacknowledged data.
The User Datagram Protocol provides data transfer without many of the reliable delivery capabilities of TCP. UDP is less CPU-intensive than TCP and is useful when guaranteed data delivery is not of paramount importance.
Translates between DARPA Internet and Ethernet addresses. See arp(ADMN) and arp(ADMP).
Handles error-message and protocol control for TCP/IP. See icmp(ADMP).
Provides both synchronous and asynchronous network connections over a serial line. See ppp(ADMP) and ``Configuring the Point-to-Point Protocol (PPP)''.
Translates between Ethernet and DARPA Internet addresses.
Enables IP over serial lines. See slip(ADMP) and ``Configuring the Serial Line Internet Protocol (SLIP)''.
Used by MMDF to send mail via TCP/IP.
Performs distributed network management functions via TCP/IP. See ``Configuring the Simple Network Management Protocol (SNMP)''.
In the UNIX system, most server programs are started by a super server, called the ``Internet daemon''. The Internet daemon, /etc/inetd, acts as a master server for programs specified in its configuration file, /etc/inetd.conf. It listens for service requests for these servers, and starts up the appropriate program whenever a request is received. The configuration file includes information about:
daytime stream tcp nowait root internalConsult inetd.conf(SFF) for more details on the format of the configuration file and the operation of the Internet daemon. Several data files are used by the network library routines and server programs. Most of these files are host independent and are updated only rarely.
Network database files
|list of known services
|list of ``trusted'' hosts
|list of ``unwelcome'' ftp users
|list of servers started by inetd
The files distributed are set up for Internet hosts. Local networks and hosts should be added to the databases to describe the local configuration.
Several TCP/IP commands, described in detail on their manual pages, provide end users with networking capabilities:
|file transfer between machines running TCP/IP (these machines may or may not run the same operating system)
|remote command execution on another UNIX system
|file copying between two UNIX systems
|remote login on another UNIX system
|status display of local network machines
|display list of users logged on to local network machines.
|remote login on a machine running TCP/IP (these machines may or may not run the same operating system)
To configure TCP/IP, you must:
Basic administration of TCP/IP consists of: