System Administration Guide: IP Services

Introducing the Internet Protocol Suite

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.

TCP/IP is the abbreviation 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, the “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 network number. At the time of this writing, the InterNIC organization assigns IP network numbers.

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 also handles the registration of domain names under certain top-level domains such as .com (commercial), .edu (education), and .gov (government). Chapter 3, Planning Your TCP/IP Network (Task) contains more information about the InterNIC. For more information on DNS, refer to System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP).

Protocol Layers and the OSI Model

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. Each layer exists on both the sending and receiving hosts. A specific layer on one machine sends or receives exactly the same object that another machine's peer process sends or receives. These activities occur independently from activities in layers above or below the layer under consideration. Effectively, each layer on a host acts independently of other layers on the same machine. Each layer acts in parallel with the same layer on other hosts.

OSI Reference Model

Most network protocol suites are viewed as 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. Each layer associates one or more protocols with the layer. The layers represent data transfer operations common to all types of data transfers among cooperating networks.

The OSI Reference Model lists the protocol layers from the top (layer 7) to the bottom (layer 1). The following table shows the model.

Table 2–1 Open Systems Interconnection Reference Model

Layer No. 

Layer Name 



Consists of standard communication services and applications that everyone can use. 


Ensures that information is delivered to the receiving machine in a form that the machine can understand. 


Manages the connections and terminations between cooperating computers. 


Manages the transfer of data. Also assures that the received data are identical to the transmitted data. 


Manages data addressing and delivery between networks. 

Data Link

Handles the transfer of data across the network media. 


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 Reference 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.

TCP/IP Protocol Architecture Model

The OSI model describes an idealized network communications with a family of protocols. TCP/IP does not correspond to this model directly. 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 lowest (physical network).

Table 2–2 TCP/IP Protocol Stack

OSI Ref. Layer No. 

OSI Layer Equivalent 

TCP/IP Layer 

TCP/IP Protocol Examples 


Application, session, presentation 


NFS, NIS+, DNS, telnet, ftp, rlogin, rsh, rcp, RIP, RDISC, SNMP, and others







Data link 

Data link

PPP, IEEE 802.2 


Physical network

Ethernet (IEEE 802.3) Token Ring, RS-232, others  

The table shows the TCP/IP protocol layers. Also shown are the OSI Model equivalents with examples of the protocols that are available at each level of the TCP/IP protocol stack. Each host that is involved in a communication transaction runs a unique implementation of the protocol stack.

Physical Network Layer

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.

Data-Link Layer

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.

Internet Layer

This layer, also known as the network 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).

IP Protocol

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:

Previous releases of the Solaris operating environment implement version 4 of the Internet Protocol, which is abbreviated as IPv4. However, because of the rapid growth of the Internet, a new Internet Protocol was created. The new protocol increases address space. This new version, known as version 6, is abbreviated as IPv6. The Solaris operating environment supports both versions, which are described in this book. To avoid confusion when addressing the Internet Protocol, one of the following conventions is used:

ARP Protocol

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).

ICMP Protocol

Internet Control Message Protocol (ICMP) detects and reports network error conditions. ICMP reports on the following:

The ping Command contains more information on the operating system commands that use ICMP for error detection.

Transport Layer

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 Protocol

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 discrete 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 Protocol

UDP, the other transport layer protocol, 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 rather than TCP.

Application Layer

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

UNIX “r” Commands

The UNIX “r” commands enable users to issue commands on their local machines that run on the remote host. These commands include the following:

Instructions for using these commands are in rcp(1), rlogin(1), and rsh(1) man pages.

Name Services

The Solaris operating environment provides the following naming services:

Directory Service

The Solaris operating environment supports LDAP (Lightweight Directory Access Protocol) in conjunction with the iPlanet Directory Server 5.x, as well as other LDAP Directory Servers. The distinction between a Naming 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).

File Services

The NFS application layer protocol provides file services for the Solaris operating environment. You can find complete information about the NFS service in System Administration Guide: Resource Management and Network Services.

Network Administration

The Simple Network Management Protocol (SNMP) enables you to view the layout of your network and view the status of key machines. SNMP also enables you to obtain complex network statistics from software that is based on a graphical user interface. Many companies offer network management packages that implement SNMP. SunNet ManagerTM software is an example.

Routing Protocols

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.