13. Internet Information Resources

13.1 The World Wide Web

The primary method used to retrieve network information is the World Wide Web. The Web is an interlinked network of hypertext servers based on the Hypertext Transfer Protocol (HTTP) that runs on top of TCP/IP. The Web is accessed via a browser, a program that provides a consistent graphical interface to the user. All of the popular UNIX browsers - Netscape, Mosaic, Arena, etc. - are modeled after the original Mosaic browser developed at the National Center for Supercomputer Applications (NCSA). Therefore, they share a common look and feel.

Most UNIX systems do not ship with a built-in browser; you need to download one from the Internet. The Netscape browser is available at the URL http://www.netscape.com. It can be downloaded, evaluated, and then purchased. (It's nice to be able to try before you buy!) The Mosaic browser is available free of charge at ftp://ftp.ncsa.edu/Web/Mosaic/Unix/binaries. They both work well and in an almost identical manner. However, Netscape is the most popular browser and has an active development team.

Obtaining information from hypertext Web pages is the most common use for a browser. Use yours to keep up with the most current network information. Figure 13.1 shows a network administrator checking the security alerts at the Computer Security Resource Clearinghouse at the National Institute of Standards and Technology.

Figure 13.1: Security alerts website

"Location" or "Netsite," but in all cases it performs the same function: it holds the path to the information resource. In the example the location is http://csrc.nist.gov/secalert/. "URL" stands for universal resource locator. It is a standard way of defining a network resource and it has a specific structure:

service://server/path/file

In the sample URL, http is the service; csrc.nist.gov is the server; and secalerts is the path to the resource contained on that server. This tells the browser to locate a host with the domain name csrc.nist.gov, and to ask it for the hypertext information located in the secalerts one of the services that can be specified in a URL.

A Web browser can be used to view local hypertext files. This is how the gated documentation is delivered. Figure 13.2 shows a network administrator reading the gated documentation. The URL in Figure 13.2 is file://localhost/usr/doc/config_guide/config.html. The service is file, which means that the resource is to be read via the standard filesystem. The server is the local host (localhost). The path is /usr/doc/config_gated, and the file is config.html.

Figure 13.2: Reading GateD documentation

Another browser service that is often used by a network administrator is FTP. Figure 13.3 shows a network administrator using a browser to download software. The URL in Figure 13.3 is ftp://ftp.ncsa.edu/Web/Mosaic/Unix/binaries/2.6. FTP is the service used to access the resource, which in this case is a binary file. The server is ftp.ncsa.edu, which is the anonymous FTP server at the National Center for Super Computing Applications. The path is /Web/Mosaic/Unix/binaries/2.6 and the file is any of the files listed on the screen.

Figure 13.3: Browser FTP interface

be done with a browser and a huge number of resources available on the network. A detailed discussion of browsers and the Web is beyond the scope of this book. See The Whole Internet User's Guide and Catalog, by Ed Krol (O'Reilly & Associates), for a full treatment of these subjects.

fastest or most efficient way to download a file. Figure 13.3 shows a file being downloaded from an anonymous FTP server. An alternative is to invoke ftp directly from the command-line interface.