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. 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 NFS

• Simple Network Management Protocol (SNMP), which enables network management

• RIP and RDISC routing protocols

Standard TCP/IP Services

• 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. 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.

UNIX "r" Commands

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 Solaris Advanced User's Guide and in rcp(1), rlogin(1), and rsh(1) man pages.

Name Services

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.

File Services

The NFS application layer protocol provides file services for the Solaris operating system. You can find complete information about the NFS service in NFS Administration Guide.

Network Administration

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 Manager^TM 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 Chapter 5, Configuring Routers.