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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.



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