This chapter introduces the Solaris implementation of the TCP/IP network protocol suite. The information is intended for system and network administrators who are unfamiliar with basic TCP/IP concepts. The remaining parts of this book assume that you are familiar with these concepts.This chapter contains the following information:Introducing the TCP/IP Protocol Suite How the TCP/IP Protocols Handle Data Communications Finding Out More About TCP/IP and the Internet This section presents an in-depth introduction to the protocols that are included in TCP/IP. Although the information is conceptual, you should learn the names of the protocols. You should also learn what each protocol does. “TCP/IP” is the acronym that is commonly used for the set of network protocols that compose the Internet Protocol suite. Many texts use the term “Internet” to describe both the protocol suite and the global wide area network. In this book, “TCP/IP” refers specifically to the Internet protocol suite. “Internet” refers to the wide area network and the bodies that govern the Internet.To interconnect your TCP/IP network with other networks, you must obtain a unique IP address for your network. At the time of this writing, you obtain this address from an Internet service provider (ISP).If hosts on your network are to participate in the Internet Domain Name System (DNS), you must obtain and register a unique domain name. The InterNIC coordinates the registration of domain names through a group of worldwide registries. For more information on DNS, refer to System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP). Most network protocol suites are structured as a series of layers, sometimes collectively referred to as a protocol stack. Each layer is designed for a specific purpose. Each layer exists on both the sending and receiving systems. A specific layer on one system sends or receives exactly the same object that another system's peer process sends or receives. These activities occur independently from activities in layers above or below the layer under consideration. In essence, each layer on a system acts independently of other layers on the same system. Each layer acts in parallel with the same layer on other systems.Most network protocol suites are structured in layers. The International Organization for Standardization (ISO) designed the Open Systems Interconnection (OSI) Reference Model that uses structured layers. The OSI model describes a structure with seven layers for network activities. One or more protocols is associated with each layer. The layers represent data transfer operations that are common to all types of data transfers among cooperating networks. The OSI model lists the protocol layers from the top (layer 7) to the bottom (layer 1). The following table shows the model.Layer No. Layer Name Description 7 Application Consists of standard communication services and applications that everyone can use. 6 Presentation Ensures that information is delivered to the receiving system in a form that the system can understand. 5 Session Manages the connections and terminations between cooperating systems. 4 Transport Manages the transfer of data. Also assures that the received data are identical to the transmitted data. 3 Network Manages data addressing and delivery between networks. 2 Data link Handles the transfer of data across the network media. 1 Physical Defines the characteristics of the network hardware. The OSI model defines conceptual operations that are not unique to any particular network protocol suite. For example, the OSI network protocol suite implements all seven layers of the OSI model. TCP/IP uses some of OSI model layers. TCP/IP also combines other layers. Other network protocols, such as SNA, add an eighth layer. The OSI model describes idealized network communications with a family of protocols. TCP/IP does not directly correspond to this model. TCP/IP either combines several OSI layers into a single layer, or does not use certain layers at all. The following table shows the layers of the Solaris implementation of TCP/IP. The table lists the layers from the topmost layer (application) to the bottommost layer (physical network). OSI Ref. Layer No. OSI Layer Equivalent TCP/IP Layer TCP/IP Protocol Examples 5,6,7 Application, session, presentation Application NFS, NIS, DNS, LDAP, telnet, ftp, rlogin, rsh, rcp, RIP, RDISC, SNMP, and others 4 Transport Transport TCP, UDP, SCTP 3 Network Internet IPv4, IPv6, ARP, ICMP 2 Data link Data link PPP, IEEE 802.2 1 Physical Physical network Ethernet (IEEE 802.3), Token Ring, RS-232, FDDI, and others The table shows the TCP/IP protocol layers and the OSI model equivalents. Also shown are examples of the protocols that are available at each level of the TCP/IP protocol stack. Each system that is involved in a communication transaction runs a unique implementation of the protocol stack. The physical network layer specifies the characteristics of the hardware to be used for the network. For example, physical network layer specifies the physical characteristics of the communications media. The physical layer of TCP/IP describes hardware standards such as IEEE 802.3, the specification for Ethernet network media, and RS-232, the specification for standard pin connectors. The data-link layer identifies the network protocol type of the packet, in this instance TCP/IP. The data-link layer also provides error control and “framing.” Examples of data-link layer protocols are Ethernet IEEE 802.2 framing and Point-to-Point Protocol (PPP) framing. The Internet layer, also known as the network layer or IP layer, accepts and delivers packets for the network. This layer includes the powerful Internet Protocol (IP), the Address Resolution Protocol (ARP), and the Internet Control Message Protocol (ICMP). The IP protocol and its associated routing protocols are possibly the most significant of the entire TCP/IP suite. IP is responsible for the following: IP addressing – The IP addressing conventions are part of the IP protocol. Designing an IPv4 Addressing Scheme introduces IPv4 addressing and IPv6 Addressing Overview introduces IPv6 addressing. Host-to-host communications – IP determines the path a packet must take, based on the receiving system's IP address. Packet formatting – IP assembles packets into units that are known as datagrams. Datagrams are fully described in Internet Layer: Where Packets Are Prepared for Delivery. Fragmentation – If a packet is too large for transmission over the network media, IP on the sending system breaks the packet into smaller fragments. IP on the receiving system then reconstructs the fragments into the original packet. The Solaris OS supports both IPv4 and IPv6 addressing formats, which are described in this book. To avoid confusion when addressing the Internet Protocol, one of the following conventions is used:When the term “IP” is used in a description, the description applies to both IPv4 and IPv6. When the term “IPv4” is used in a description, the description applies only to IPv4. When the term “IPv6” is used in a description, the description applies only to IPv6. The Address Resolution Protocol (ARP) conceptually exists between the data-link and Internet layers. ARP assists IP in directing datagrams to the appropriate receiving system by mapping Ethernet addresses (48 bits long) to known IP addresses (32 bits long). The Internet Control Message Protocol (ICMP) detects and reports network error conditions. ICMP reports on the following: Dropped packets – Packets that arrive too fast to be processed Connectivity failure – A destination system cannot be reached Redirection – Redirecting a sending system to use another router Chapter 8, Administering a TCP/IP Network (Tasks) contains more information on the Solaris OS commands that use ICMP for error detection. The TCP/IP transport layer ensures that packets arrive in sequence and without error, by swapping acknowledgments of data reception, and retransmitting lost packets. This type of communication is known as end-to-end. Transport layer protocols at this level are Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Stream Control Transmission Protocol (SCTP). TCP and SCTP provide reliable, end-to-end service. UDP provides unreliable datagram service.TCP enables applications to communicate with each other as though they were connected by a physical circuit. TCP sends data in a form that appears to be transmitted in a character-by-character fashion, rather than as discrete packets. This transmission consists of the following:Starting point, which opens the connection Entire transmission in byte order Ending point, which closes the connection. TCP attaches a header onto the transmitted data. This header contains many parameters that help processes on the sending system connect to peer processes on the receiving system.TCP confirms that a packet has reached its destination by establishing an end-to-end connection between sending and receiving hosts. TCP is therefore considered a “reliable, connection-oriented” protocol. SCTP is a reliable, connection-oriented transport layer protocol that provides the same services to applications that are available from TCP. Moreover, SCTP can support connections between systems that have more than one address, or multihomed. The SCTP connection between sending and receiving system is called an association. Data in the association is organized in chunks. Because SCTP supports multihoming, certain applications, particularly applications used by the telecommunications industry, need to run over SCTP, rather than TCP. UDP provides datagram delivery service. UDP does not verify connections between receiving and sending hosts. Because UDP eliminates the processes of establishing and verifying connections, applications that send small amounts of data use UDP. The application layer defines standard Internet services and network applications that anyone can use. These services work with the transport layer to send and receive data. Many application layer protocols exist. The following list shows examples of application layer protocols: Standard TCP/IP services such as the ftp, tftp, and telnet commands UNIX “r” commands, such as rlogin and rsh Name services, such as NIS and the domain name system (DNS) Directory services (LDAP) File services, such as the NFS service Simple Network Management Protocol (SNMP), which enables network management Router Discovery Server protocol (RDISC) and Routing Information Protocol (RIP) routing protocols FTP and Anonymous FTP – The File Transfer Protocol (FTP) transfers files to and from a remote network. The protocol includes the ftp command and the in.ftpd daemon. FTP enables a user to specify the name of the remote host and file transfer command options on the local host's command line. The in.ftpd daemon on the remote host then handles the requests from the local host. Unlike rcp, ftp works even when the remote computer does not run a UNIX based operating system. A user must log in to the remote system to make an ftp connection, unless the remote system has been configured to allow anonymous FTP. You can obtain an enormous amount of material from anonymous FTP servers that are connected to the Internet. Universities and other institutions set up these servers to offer software, research papers, and other information to the public domain. When you log in to this type of server, you use the login name anonymous, hence the term “anonymous FTP server.” Using anonymous FTP and setting up anonymous FTP servers is outside the scope of this manual. However, many books, such as The Whole Internet User's Guide & Catalog, discuss anonymous FTP in detail. Instructions for using FTP are in System Administration Guide: Network Services. The ftp1 man page describes all ftp command options that are invoked through the command interpreter. The ftpd1M man page describes the services that are provided by the in.ftpd daemon. Telnet – The Telnet protocol enables terminals and terminal-oriented processes to communicate on a network that runs TCP/IP. This protocol is implemented as the telnet program on local systems and the in.telnetd daemon on remote machines. Telnet provides a user interface through which two hosts can communicate on a character-by-character or line-by-line basis. Telnet includes a set of commands that are fully documented in the telnet1 man page. TFTP – The Trivial File Transfer Protocol (tftp) provides functions that are similar to ftp, but the protocol does not establish ftp's interactive connection. As a result, users cannot list the contents of a directory or change directories. A user must know the full name of the file to be copied. The tftp1man page describes the tftp command set. The UNIX “r” commands enable users to issue commands on their local machines that run on the remote host. These commands include the following:rcp rlogin rsh Instructions for using these commands are in the rcp1, rlogin1, and rsh1 man pages. The Solaris OS provides the following name services:DNS – The domain name system (DNS) is the name service provided by the Internet for TCP/IP networks. DNS provides host names to the IP address service. DNS also serves as a database for mail administration. For a complete description of this service, see System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP). See also the resolver3RESOLV man page. /etc files – The original host-based UNIX name system was developed for standalone UNIX machines and then adapted for network use. Many old UNIX operating systems and computers still use this system, but it is not well suited for large complex networks. NIS – Network Information Service (NIS) was developed independently of DNS and has a slightly different focus. Whereas DNS focuses on making communication simpler by using machine names instead of numerical IP addresses, NIS focuses on making network administration more manageable by providing centralized control over a variety of network information. NIS stores information about machine names and addresses, users, the network itself, and network services. NIS name space information is stored in NIS maps. For more information on NIS Architecture and NIS Administration, see System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP). The Solaris OS supports LDAP (Lightweight Directory Access Protocol) in conjunction with the Sun Open Net Environment (Sun ONE) Directory Server, as well as other LDAP directory servers. The distinction between a name service and a directory service is in the differing extent of functionality. A directory service provides the same functionality of a naming service, but provides additional functionalities as well. See System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP). The NFS application layer protocol provides file services for the Solaris OS. You can find complete information about the NFS service in System Administration Guide: Network Services. The Simple Network Management Protocol (SNMP) enables you to view the layout of your network and the status of key machines. SNMP also enables you to obtain complex network statistics from software that is based on a graphical user interface (GUI). Many companies offer network management packages that implement SNMP. The Routing Information Protocol (RIP) and the Router Discovery Server Protocol (RDISC) are two routing protocols for TCP/IP networks. They are described in Routing Protocols in the Solaris OS. When a user issues a command that uses a TCP/IP application layer protocol, a series of events is initiated. The user's command or message passes through the TCP/IP protocol stack on the local system. Then, the command or message passes across the network media to the protocols on the remote system. The protocols at each layer on the sending host add information to the original data. Protocols on each layer of the sending host also interact with their peers on the receiving host. Figure 1–1 shows this interaction.The packet is the basic unit of information that is transferred across a network. The basic packet consists of a header with the sending and receiving systems' addresses, and a body, or payload, with the data to be transferred. As the packet travels through the TCP/IP protocol stack, the protocols at each layer either add or remove fields from the basic header. When a protocol on the sending system adds data to the packet header, the process is called data encapsulation. Moreover, each layer has a different term for the altered packet, as shown in the following figure.

Diagram shows how a packet travels through the TCP/IP stack from the sending host to the receiving host.

This section summarizes the life cycle of a packet. The life cycle starts when you issue a command or send a message. The life cycle finishes when the appropriate application on the receiving system receives the packet. The packet's history begins when a user on one system sends a message or issues a command that must access a remote system. The application protocol formats the packet so that the appropriate transport layer protocol, TCP or UDP, can handle the packet. Suppose the user issues an rlogin command to log in to the remote system, as shown in Figure 1–1. The rlogin command uses the TCP transport layer protocol. TCP expects to receive data in the form of a stream of bytes that contain the information in the command. Therefore, rlogin sends this data as a TCP stream. When the data arrives at the transport layer, the protocols at the layer start the process of data encapsulation. The transport layer encapsulates the application data into transport protocol data units. The transport layer protocol creates a virtual flow of data between the sending and receiving application, differentiated by the transport port number. The port number identifies a port, a dedicated location in memory for receiving or sending data. In addition, the transport protocol layer might provide other services, such as reliable, in order data delivery. The end result depends on whether TCP, SCTP, or UDP handles the information.TCP is often called a “connection-oriented” protocol because TCP ensures the successful delivery of data to the receiving host. Figure 1–1 shows how the TCP protocol receives the stream from the rlogin command. TCP then divides the data that is received from the application layer into segments and attaches a header to each segment. Segment headers contain sending and receiving ports, segment ordering information, and a data field that is known as a checksum. The TCP protocols on both hosts use the checksum data to determine if the data transfers without error. TCP uses segments to determine whether the receiving system is ready to receive the data. When the sending TCP wants to establish connections, TCP sends a segment that is called a SYN to the TCP protocol on the receiving host. The receiving TCP returns a segment that is called an ACK to acknowledge the successful receipt of the segment. The sending TCP sends another ACK segment, then proceeds to send the data. This exchange of control information is referred to as a three-way handshake. UDP is a “connectionless” protocol. Unlike TCP, UDP does not check that data arrived at the receiving host. Instead, UDP formats the message that is received from the application layer into UDP packets. UDP attaches a header to each packet. The header contains the sending and receiving ports, a field with the length of the packet, and a checksum. The sending UDP process attempts to send the packet to its peer UDP process on the receiving host. The application layer determines whether the receiving UDP process acknowledges the reception of the packet. UDP requires no notification of receipt. UDP does not use the three-way handshake. The transport protocols TCP, UDP, and SCTP pass their segments and packets down to the Internet layer, where the IP protocol handles the segments and packets. IP prepares them for delivery by formatting them into units called IP datagrams. IP then determines the IP addresses for the datagrams, so that they can be delivered effectively to the receiving host. IP attaches an IP header to the segment or packet's header, in addition to the information that is added by TCP or UDP. Information in the IP header includes the IP addresses of the sending and receiving hosts, the datagram length, and the datagram sequence order. This information is provided if the datagram exceeds the allowable byte size for network packets and must be fragmented. Data-link layer protocols, such as PPP, format the IP datagram into a frame. These protocols attach a third header and a footer to “frame” the datagram. The frame header includes a cyclic redundancy check (CRC) field that checks for errors as the frame travels over the network media. Then, the data-link layer passes the frame to the physical layer. The physical network layer on the sending host receives the frames and converts the IP addresses into the hardware addresses appropriate to the network media. The physical network layer then sends the frame out over the network media. When the packet arrives on the receiving host, the packet travels through the TCP/IP protocol stack in the reverse order from which it was sent. Figure 1–1 illustrates this path. Moreover, each protocol on the receiving host strips off header information that is attached to the packet by its peer on the sending host. The following process occurs:The physical network layer receives the packet in its frame form. The physical network layer computes the CRC of the packet, then sends the frame to the data link layer. The data-link layer verifies that the CRC for the frame is correct and strips off the frame header and the CRC. Finally, the data-link protocol sends the frame to the Internet layer. The Internet layer reads information in the header to identify the transmission. Then, the Internet layer determines if the packet is a fragment. If the transmission is fragmented, IP reassembles the fragments into the original datagram. IP then strips off the IP header and passes the datagram on to transport layer protocols. The transport layer (TCP, SCTP, and UDP) reads the header to determine which application layer protocol must receive the data. Then, TCP, SCTP, or UDP strips off its related header. TCP, SCTP, or UDP sends the message or stream to the receiving application. The application layer receives the message. The application layer then performs the operation that the sending host requested. TCP/IP provides internal trace support by logging TCP communication when an RST packet terminates a connection. When an RST packet is transmitted or received, information on as many as 10 packets, which were just transmitted, is logged with the connection information. Information about TCP/IP and the Internet is widely available. If you require specific information that is not covered in this text, you can probably find what you need in the sources cited next. Many trade books about TCP/IP and the Internet are available from your local library or computer bookstore. The following two books are considered the classic texts on TCP/IP:Craig Hunt. TCP/IP Network Administration – This book contains some theory and much practical information for managing a heterogeneous TCP/IP network. W. Richard Stevens. TCP/IP Illustrated, Volume I – This book is an in-depth explanation of the TCP/IP protocols. This book is ideal for network administrators who require a technical background in TCP/IP and for network programmers. The Internet has a wealth of web sites and user groups that are devoted to TCP/IP protocols and their administration. Many manufacturers, including Sun Microsystems, offer web-based resources for general TCP/IP information. The following are helpful web resources for TCP/IP information and general system administration information.Web Site Description The Internet Engineering Task Force (IETF) web site The IETF is the body responsible for the architecture and governance of the Internet. The IETF web site contains information about the various activities of this organization. The site also includes links to the major publications of the IETF. Sun Microsystem's BigAdmin Portal BigAdmin provides information for administering Sun computers. The site offers FAQs, resources, discussions, links to documentation, and other materials that pertain to Solaris OS administration, including networking. The Internet Engineering Task Force (IETF) working groups publish standards documents that are known as Requests for Comments (RFCs). Standards that are under development are published in Internet Drafts. The Internet Architecture Board (IAB) must approve all RFCs before they are placed in the public domain. Typically RFCs and Internet drafts are directed to developers and other highly technical readers. However, a number of RFCs that deal with TCP/IP topics contain valuable information for system administrators. These RFCs are cited in various places throughout this book.Generally, For Your Information (FYI) documents appear as a subset of the RFCs. FYIs contain information that does not deal with Internet standards. FYIs contain Internet information of a more general nature. For example, FYI documents include a bibliography that list introductory TCP/IP books and papers. FYI documents provide an exhaustive compendium of Internet-related software tools. Finally, FYI documents include a glossary of Internet and general networking terms. You will find references to relevant RFCs throughout this guide and other books in the Solaris System Administrator Collection.