TCP/IP Protocol Suite

The TCP/IP protocol suite actually consists of different protocols, each designed for a specific task in a TCP/IP network. The three basic protocols are the Transmission Control Protocol (TCP), which handles receiving and sending out communications, the Internet Protocol (IP), which handles the actual transmissions, and the User Datagram Protocol (UDP), which also handles receiving and sending packets. The IP protocol, which is the base protocol that all others use, handles the actual transmissions, handling the packets of data with sender and receiver information in each. The TCP protocol is designed to work with cohesive messages or data. This protocol checks received packets and sorts them into their designated order, forming the original message. For data sent out, the TCP protocol breaks the data into separate packets, designating their order. The UDP protocol, meant to work on a much more raw level, also breaks down data into packets but does not check their order. The TCP/IP protocol is designed to provide stable and reliable connections that ensure that all data is received and reorganized into its original order. UDP, on the other hand, is designed to simply send as much data as possible, with no guarantee that packets will all be received or placed in the proper order. UDP is often used for transmitting very large amounts of data of the type that can survive the loss of a few packets-for example, temporary images, video, and banners displayed on the Internet.

Table 38-1: TCP/IP Protocol Development Groups

Group	Title	Description
ISOC	Internet Society	Professional membership organization of Internet experts that oversees boards and task forces dealing with network policy issues www.isoc.org
IESG	The Internet Engineering Steering Group	Responsible for technical management of IETF activities and the Internet standards process www.ietf.org/iesg.html
IANA	Internet Assigned Numbers Authority	Responsible for Internet Protocol (IP) addresses www.iana.org
IAB	Internet Architecture Board	Defines the overall architecture of the Internet, providing guidance and broad direction to the IETF www.iab.org
IETF	Internet Engineering Task Force	Protocol engineering and development arm of the Internet www.ietf.org

Other protocols provide various network and user services. The Domain Name Service (DNS) provides address resolution. The File Transfer Protocol (FTP) provides file transmission, and the Network File System (NFS) provides access to remote file systems. Table 38-2 lists the different protocols in the TCP/IP protocol suite. These protocols make use of either the TCP or UDP protocol to send and receive packets, which, in turn, uses the IP protocol for actually transmitting the packets.

Table 38-2: TCP/IP Protocol Suite

Transport	Description
TCP	Transmission Control Protocol; places systems in direct communication
UDP	User Datagram Protocol
IP	Internet Protocol; transmits data
ICMP	Internet Control Message Protocol; status messages for IP
Routing	Description
RIP	Routing Information Protocol; determines routing
OSPF	Open Shortest Path First; determines routing
Network Addresses	Description
ARP	Address Resolution Protocol; determines unique IP address of systems
DNS	Domain Name Service; translates hostnames into IP addresses
RARP	Reverse Address Resolution Protocol; determines addresses of systems
User Services	Description
FTP	File Transfer Protocol; transmits files from one system to another using TCP
TFTP	Trivial File Transfer Protocol; transfers files using UDP
Telnet	Remote login to another system on the network
SMTP	Simple Mail Transfer Protocol; transfers e-mail between systems
RPC	Remote Procedure Call; allows programs on remote systems to communicate
Gateway	Description
EGP	Exterior Gateway Protocol; provides routing for external networks
GGP	Gateway-to-Gateway Protocol; provides routing between Internet gateways
IGP	Interior Gateway Protocol; provides routing for internal networks
Network Services	Description
NFS	Network File System; allows mounting of file systems on remote machines
NIS	Network Information Service; maintains user accounts across a network
BOOTP	Boot Protocol; starts system using boot information on server for network
SNMP	Simple Network Management Protocol; provides status messages on TCP/IP configuration
DHCP	Dynamic Host Configuration Protocol; automatically provides network configuration information to host systems

In a TCP/IP network, messages are broken into small components, called datagrams, which are then transmitted through various interlocking routes and delivered to their destination computers. Once received, the datagrams are reassembled into the original message. Datagrams themselves can be broken down into smaller packets. The packet is the physical message unit actually transmitted among networks. Sending messages as small components has proved to be far more reliable and faster than sending them as one large, bulky transmission. With small components, if one is lost or damaged, only that component must be resent, whereas if any part of a large transmission is corrupted or lost, the entire message has to be resent.

The configuration of a TCP/IP network on your Linux system is implemented using a set of network configuration files (Table 38-7 later in this chapter provides a complete listing). Many of these can be managed using administrative programs, such as redhat-config-network as well as third-party tools like Webmin, on your root user desktop (see Chapter 5). You can also use the more specialized programs, such as netstat, ifconfig, Ethereal, and route. Some configuration files are easy to modify yourself using a text editor.

TCP/IP networks are configured and managed with a set of utilities: ifconfig, route, and netstat. The ifconfig utility operates from your root user desktop and enables you to configure your network interfaces fully, adding new ones and modifying others. The ifconfig and route utilities are lower-level programs that require more specific knowledge of your network to use effectively. The netstat utility provides you with information about the status of your network connections. Ethereal is a network protocol analyzer that lets you capture packets as they are transmitted across your network, selecting those you want to check.