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Solaris 8 System Administrator Collection >> System Administration Guide, Volume 3 >> 4. Overview of TCP/IP >> Introducing the Internet Protocol Suite
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This section presents an in-depth introduction to the protocols that compose TCP/IP. Although the information is conceptual, you should learn the names of the protocols and what each does. This is important because TCP/IP books explain tasks with the assumption that you understand the concepts introduced here.
TCP/IP is the commonly used nickname for the set of network protocols composing 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, the "TCP/IP" refers specifically to the Internet protocol suite; "Internet" refers to the wide-area network and the bodies that govern it.
To interconnect your TCP/IP network with other networks, you must obtain a unique IP network number. At the time of this writing, IP network numbers are assigned by an organization known as the InterNIC.
If hosts on your network are going to participate in the Internet Domain Name system (DNS), you must obtain and register a unique domain name. The InterNIC also handles the registration of domain names under certain top-level domains such as .com (commercial), .edu (education), and .gov (government). Chapter 5, Planning Your TCP/IP Network contains more information about the InterNIC. (For more information on DNS, refer to Solaris Naming Administration Guide.)
Most network protocol suites are structured as a series of layers, sometimes referred to collectively as a protocol stack. Each layer is designed for a specific purpose and exists on both the sending and receiving hosts. Each is designed so that a specific layer on one machine sends or receives exactly the same object sent or received by its peer process on another machine. These activities take place independently from what is going on in layers above or below the layer under consideration. In other words, each layer on a host acts independently of other layers on the same machine, and in concert with the same layer on other hosts.
Most network protocol suites are viewed as structured in layers. This is a result of the Open Systems Interconnect (OSI) Reference Model designed by the International Standards Organization (ISO). The OSI model describes network activities as having a structure of seven layers, each of which has one or more protocols associated with it. The layers represent data transfer operations common to all types of data transfers among cooperating networks.
The protocol layers of the OSI Reference Model are traditionally listed from the top (layer 7) to the bottom (layer 1) up, as shown in the following table.
Table 4-1 The Open Systems Interconnect Reference ModelLayer No. | Layer Name | Description |
|---|---|---|
7 | Consists of standard communication services and applications that everyone can use | |
6 | Ensures that information is delivered to the receiving machine in a form that it can understand | |
5 | Manages the connections and terminations between cooperating computers | |
4 | Manages the transfer of data and assures that received and transmitted data are identical | |
3 | Manages data addressing and delivery between networks | |
2 | Handles the transfer of data across the network media | |
1 | Defines the characteristics of the network hardware |
The operations defined by the OSI model are conceptual and not unique to any particular network protocol suite. For example, the OSI network protocol suite implements all seven layers of the OSI Reference Model. TCP/IP uses some of OSI model layers and combines others. Other network protocols, such as SNA, add an eighth layer.
The OSI model describes an idealized network communications protocol family. TCP/IP does not correspond to this model directly, as it 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, listed from topmost layer (application) to lowest (physical network).
Table 4-2 TCP/IP Protocol StackOSI Ref. Layer No. | OSI Layer Equivalent | TCP/IP Layer | TCP/IP Protocol Examples |
|---|---|---|---|
5,6,7 | Application, Session, Presentation | NFS, NIS+, DNS, telnet, ftp, rlogin, rsh, rcp, RIP, RDISC, SNMP, and others | |
4 | Transport | TCP, UDP | |
3 | Network | IP, ARP, ICMP | |
2 | Data Link | PPP, IEEE 802.2 | |
1 | Physical | Ethernet (IEEE 802.3) Token Ring, RS-232, others |
The table shows the TCP/IP protocol layers, their OSI Model equivalents, and examples of the protocols available at each level of the TCP/IP protocol stack. Each host involved in a communication transaction runs its own implementation of the protocol stack.
The physical network layer specifies the characteristics of the hardware to be used for the network. For example, it 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 case TCP/IP. It 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.
This layer, also known as the network layer, accepts and delivers packets for the network. It includes the powerful Internet protocol (IP), the Address Resolution Protocol (ARP) protocol, and the Internet Control Message Protocol (ICMP) protocol.
The IP protocol and its associated routing protocols are possibly the most significant of the entire TCP/IP suite. IP is responsible for:
IP addressing - The IP addressing conventions are part of the IP protocol. (Chapter 5, Planning Your TCP/IP Network describes IPv4 addressing in detail and Chapter 14, Overview of IPv6 describes IPv6 addressing in detail.)
Host-to-host communications - IP determines the path a packet must take, based on the receiving host's IP address.
Packet formatting - IP assembles packets into units known as IP datagrams. Datagrams are fully described in "Internet Layer".
Fragmentation - If a packet is too large for transmission over the network media, IP on the sending host breaks the packet into smaller fragments. IP on the receiving host then reconstructs the fragments into the original packet.
Previous releases of the Solaris operating environment implemented version 4 of the Internet Protocol, which is written IPv4. However, because of the rapid growth of the Internet, it was necessary to create a new Internet Protocol with improved capabilities, such as increased address space. This new version, known as version 6, is written IPv6. The Solaris operating environment supports both versions, which are described in this book. To avoid confusion when addressing the Internet Protocol, the following convention 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 host by mapping Ethernet addresses (48 bits long) to known IP addresses (32 bits long).
Internet Control Message Protocol (ICMP) is the protocol responsible for detecting network error conditions and reporting on them. ICMP reports on:
Dropped packets (when packets are arriving too fast to be processed)
Connectivity failure (when a destination host can't be reached)
Redirection (which tells a sending host to use another router)
The "ping Command" contains more information on the operating system commands that use ICMP for error detection.
The TCP/IP transport layer protocols ensure 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) and User Datagram Protocol (UDP).
TCP enables applications to communicate with each other as though 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 discreet packets. This transmission consists of a starting point, which opens the connection, the entire transmission in byte order, and an ending point, which closes the connection.
TCP attaches a header onto the transmitted data. This header contains a large number of parameters that help processes on the sending machine connect to peer processes on the receiving machine.
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.
UDP, the other transport layer protocol, provides datagram delivery service. It does not provide any means of verifying that connection was ever achieved between receiving and sending hosts. Because UDP eliminates the processes of establishing and verifying connections, applications that send small amounts of data use it rather than TCP.
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. There are many applications layer protocols, some of which you probably already use. Some of the protocols include:
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 Domain Name System (DNS)
File services, such as the NFS service
Simple Network Management Protocol (SNMP), which enables network management
FTP and Anonymous FTP - The File Transfer Protocol (FTP) transfers files to and from a remote network. The protocol includes the ftp command (local machine) and the in.ftpd daemon (remote machine). 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 computer to make an ftp connection unless it has been set up to allow anonymous FTP.
You can now obtain a wealth of materials from anonymous FTP servers connected to the Internet. These servers are set up by universities and other institutions to make certain software, research papers, and other information available to the public domain. When you log in to this type of server, you use the login name anonymous, hence the term "anonymous FTP servers."
Using anonymous FTP and setting up anonymous FTP servers is outside the scope of this manual. However, many trade books, such as The Whole Internet User's Guide & Catalog, discuss anonymous FTP in detail. Instructions for using FTP to reach standard machines are in System Administration Guide, Volume 1. The ftp(1) man page describes all ftp command options, including those invoked through the command interpreter. The ftpd(1M) man page describes the services provided by the daemon in.ftpd.
Telnet - The Telnet protocol enables terminals and terminal-oriented processes to communicate on a network running TCP/IP. It is implemented as the program telnet (on local machines) and the daemon in.telnet (on remote machines). Telnet provides a user interface through which two hosts can communicate on a character-by-character or line-by-line basis. The application includes a set of commands that are fully documented in the telnet(1) man page.
TFTP - The trivial file transfer protocol (tftp) provides functions similar to ftp, but it does not establish ftp's interactive connection. As a result, users cannot list the contents of a directory or change directories. This means that a user must know the full name of the file to be copied. The tftp(1) man page describes the tftp command set.
The UNIX "r" commands enable users to issue commands on their local machines that are actually carried out on the remote host that they specify. These commands include
rcp
rlogin
rsh
Instructions for using these commands are in rcp(1), rlogin(1), and rsh(1) man pages.
Two name services are available from the Solaris implementation of TCP/IP: NIS+ and DNS.
NIS+ - NIS+ provides centralized control over network administration services, such as mapping host names to IP and Ethernet addresses, verifying passwords, and so on. See Solaris Naming Administration Guide for complete details.
Domain Name System - The Domain Name System (DNS) provides host names to the IP address service. It also serves as a database for mail administration. For a complete description of this service, see Solaris Naming Administration Guide. See also the in.named(1M) man page.
The NFS application layer protocol provides file services for the Solaris operating environment. You can find complete information about the NFS service in Chapter 29, Solaris NFS Environment.
The Simple Network Management Protocol (SNMP) enables you to view the layout of your network, view status of key machines, and obtain complex network statistics from graphical user interface based software. Many companies offer network management packages that implement SNMP; SunNet ManagerTM software is an example.
The Routing Information Protocol (RIP) and the Router Discovery Protocol (RDISC) are two routing protocols for TCP/IP networks. They are described in "Routing Protocols".
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