TCP/IP Protocol Architecture Model
The OSI model describes an idealized network communications with a familyof protocols. TCP/IP does not correspond to this model directly. TCP/IP eithercombines several OSI layers into a single layer, or does not use certain layersat all. The following table shows the layers of the Solaris implementationof 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 |
|---|---|---|---|
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. Also shown are the OSI Modelequivalents with examples of the protocols that are available at each levelof the TCP/IP protocol stack. Each host that is involved in a communicationtransaction runs a unique implementation of the protocol stack.
Physical Network Layer
The physical network layer specifies the characteristics of the hardwareto be used for the network. For example, physical network layer specifiesthe physical characteristics of the communications media. The physical layerof TCP/IP describes hardware standards such as IEEE 802.3, the specificationfor Ethernet network media, and RS-232, the specification for standard pinconnectors.
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 andPoint-to-Point Protocol (PPP) framing.
Internet Layer
This layer, also known as the network layer, accepts and delivers packetsfor 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 themost significant of the entire TCP/IP suite. IP is responsible for the following:
IP addressing – The IP addressingconventions are part of the IP protocol. Chapter3, Planning Your TCP/IP Network (Task) describesIPv4 addressing in detail and Chapter14, IPv6 (Overview) describes IPv6 addressingin detail.
Host-to-host communications – IPdetermines the path a packet must take, based on the receiving host's IP address.
Packet formatting – IP assemblespackets into units that are known as IP datagrams. Datagramsare fully described in Internet Layer.
Fragmentation – If a packet istoo large for transmission over the network media, IP on the sending hostbreaks the packet into smaller fragments. IP on the receiving host then reconstructsthe fragments into the original packet.
Previous releases of the Solaris operating environment implement version4 of the Internet Protocol, which is abbreviated as IPv4. However, becauseof the rapid growth of the Internet, a new Internet Protocol was created.The new protocol increases address space. This new version, known as version6, is abbreviated as IPv6. The Solaris operating environment supports bothversions, which are described in this book. To avoid confusion when addressingthe Internet Protocol, one of the following conventions is used:
When the term IP is used in a description, the descriptionapplies to both IPv4 and IPv6.
When the term IPv4 is used in a description, the descriptionapplies only to IPv4.
When the term IPv6 is used in a description, the descriptionapplies only to IPv6.
ARP Protocol
The Address Resolution Protocol (ARP) conceptually exists between thedata-link and Internet layers. ARP assists IP in directing datagrams to theappropriate receiving host by mapping Ethernet addresses (48 bits long) toknown IP addresses (32 bits long).
ICMP Protocol
Internet Control Message Protocol (ICMP) detects and reports networkerror conditions. ICMP reports on the following:
Dropped packets – Packets that arrive too fast to beprocessed
Connectivity failure – A destination host that cannotbe reached)
Redirection – Redirecting a sending host to use anotherrouter
The ping Command contains more information on the operatingsystem commands that use ICMP for error detection.
Transport Layer
The TCP/IP transport layer protocols ensure that packets arrive in sequenceand without error, by swapping acknowledgments of data reception, and retransmittinglost 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 connectedby a physical circuit. TCP sends data in a form that appears to be transmittedin a character-by-character fashion, rather than as discrete packets. Thistransmission consists of a starting point, which opens the connection, theentire transmission in byte order, and an ending point, which closes the connection.
TCP attaches a header onto the transmitted data. This header containsa large number of parameters that help processes on the sending machine connectto peer processes on the receiving machine.
TCP confirms that a packet has reached its destination by establishingan end-to-end connection between sending and receiving hosts. TCP is thereforeconsidered a “reliable, connection-oriented” protocol.
UDP Protocol
UDP, the other transport layer protocol, provides datagram deliveryservice. 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 networkapplications that anyone can use. These services work with the transport layerto send and receive data. Many application layer protocols exist. The followinglist shows examples of application layer protocols:
Standard TCP/IP services such as the ftp, tftp, and telnet commands
UNIX “r” commands, such as rloginand 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 networkmanagement
Standard TCP/IP Services
FTP and Anonymous FTP – The FileTransfer Protocol (FTP) transfers files to and from a remote network. Theprotocol includes the ftp command (local machine) and the in.ftpd daemon (remote machine). FTP enables a user to specify thename of the remote host and file transfer command options on the local host'scommand line. The in.ftpd daemon on the remote host thenhandles the requests from the local host. Unlike rcp, ftp works even when the remote computer does not run a UNIX-basedoperating system. A user must log in to the remote computer to make an ftp connection unless the remote computer has been configured toallow anonymous FTP.
You can now obtain an enormous amount of materials from anonymousFTP servers that are connected to the Internet. Universities andother institutions set up these servers to offer software, research papers,and other information to the public domain. When you log in to this type ofserver, you use the login name anonymous, hence the term “anonymousFTP servers.”
Using anonymous FTP and setting up anonymous FTP servers is outsidethe scope of this manual. However, many books, such as The WholeInternet User's Guide & Catalog, discuss anonymous FTP in detail.Instructions for using FTP to reach standard machines are in System Administration Guide: Resource Managementand Network Services. The ftp(1) man page describes all ftp command options that are invoked through the command interpreter.The ftpd(1M)man page describes the services that are provided by the daemon in.ftpd.
Telnet – The Telnet protocol enablesterminals and terminal-oriented processes to communicate on a network thatruns TCP/IP. This protocol is implemented as the program telnet(on local machines) and the daemon in.telnetd (on remotemachines). Telnet provides a user interface through which two hosts can communicateon a character-by-character or line-by-line basis. The application includesa set of commands that are fully documented in the telnet(1) man page.
TFTP – The Trivial File TransferProtocol (tftp) provides functions that are similar to ftp, but the protocol does not establish ftp'sinteractive connection. As a result, users cannot list the contents of a directoryor change directories. A user must know the full name of the file to be copied.The telnet(1)man page describes the tftp command set.
UNIX “r” Commands
The UNIX “r” commands enable users to issue commands ontheir local machines that run on the remote host. These commands include thefollowing:
rcp
rlogin
rsh
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:
DNS – The domain name system (DNS)is the naming service provided by the Internet for TCP/IP networks. DNS provideshost names to the IP address service. DNS also serves as a database for mailadministration. For a complete description of this service, see System Administration Guide: Naming and DirectoryServices (DNS, NIS, and LDAP). See also the resolver(3RESOLV) manpage.
/etc files –The original host-based UNIX™ naming system was developed for standaloneUNIX™ machines and then adapted for network use. Many old UNIX™operating systems and machines still use this system, but it is not well suitedfor 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 namesinstead of numerical IP addresses, NIS focuses on making network administrationmore manageable by providing centralized control over a variety of networkinformation. NIS stores information about machine names and addresses, users,the network itself, and network services. NIS namespace information is storedin NIS maps. For more information on NIS Architecture and NIS Administration,see System AdministrationGuide: Naming and Directory Services (DNS, NIS, and LDAP).
NIS+ – NIS+ provides centralizedcontrol over network administration services, such as mapping host names toIP and Ethernet addresses, verifying passwords, and so on. See System Administration Guide: Naming and DirectoryServices (FNS and NIS+).
FNS – Federated Naming Service(FNS), supports the use of different autonomous naming systems in a singleSolaris operating environment. FNS allows you to use a single, simple namingsystem interface for all of the different name services on your network. FNSconforms to the X/Open federated naming (XFN) specification. FNS is not areplacement for NIS+, NIS, DNS, or /etc files. Rather,FNS is implemented on top of these services and allows you to use a set ofcommon names with desktop applications. See System Administration Guide: Naming and DirectoryServices (FNS and NIS+).
Directory Service
The Solaris operating environment supports LDAP (Lightweight DirectoryAccess Protocol) in conjunction with the iPlanet Directory Server 5.x, aswell as other LDAP Directory Servers. The distinction between a Naming Serviceand a Directory Service is in the differing extent of functionality. A directoryservice provides the same functionality of a naming service, but providesadditional functionalities as well. See System Administration Guide: Naming and Directory Services (DNS, NIS, andLDAP).
File Services
The NFS application layer protocol provides file services for the Solarisoperating environment. You can find complete information about the NFS servicein System AdministrationGuide: Resource Management and Network Services.
Network Administration
The Simple Network Management Protocol (SNMP) enables you to view thelayout of your network and view the status of key machines. SNMP also enablesyou to obtain complex network statistics from software that is based on agraphical user interface. Many companies offer network management packagesthat implement SNMP. SunNet ManagerTM software is anexample.
Routing Protocols
The Routing Information Protocol (RIP) and the Router Discovery Protocol(RDISC) are two routing protocols for TCP/IP networks. They are describedin Routing Protocols.
