TCP/IP Network Administration- P12

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TCP/IP Network Administration- P12

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  1. [Chapter 13] Internet Information Resources some other browsers this field is labeled "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 path. Hypertext is not the only type of information that can be retrieved by a browser. The browser is intended to provide a consistent interface to various types of network resources. HTTP is only 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 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_01.htm (3 of 6) [2001-10-15 09:19:02]
  2. [Chapter 13] Internet Information Resources 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 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_01.htm (4 of 6) [2001-10-15 09:19:02]
  3. [Chapter 13] Internet Information Resources Reading important announcements and documentation and downloading files are probably the most common uses a network administrator has for a Web browser. There are, however, many other things that can 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. The browser provides a consistent interface to a variety of network services. But it is not the only way, or necessarily the best way, to access all of these services. In particular, it may not be the 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. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_01.htm (5 of 6) [2001-10-15 09:19:02]
  4. [Chapter 13] Internet Information Resources Previous: 12.9 Summary TCP/IP Network Next: 13.2 Anonymous FTP Administration 12.9 Summary Book Index 13.2 Anonymous FTP [ Library Home | DNS & BIND | TCP/IP | sendmail | sendmail Reference | Firewalls | Practical Security ] Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_01.htm (6 of 6) [2001-10-15 09:19:02]
  5. [Chapter 13] 13.2 Anonymous FTP Previous: 13.1 The World Chapter 13 Next: 13.3 Finding Files Internet Information Wide Web Resources 13.2 Anonymous FTP Anonymous FTP is mentioned throughout this book as a technique for retrieving publicly available files and programs from the many FTP servers around the Internet. Anonymous FTP is simply an ftp session in which you log into the remote server using the username anonymous and, by convention, your email address as the password. [1] The anonymous FTP example below should make this simple process clear: [1] Some FTP servers request your real username as a password. % ftp ftp.ncsa.edu Connected to ftp.ncsa.uiuc.edu. 220 FTP server Wed May 21 1997 ready. Name (ftp.ncsa.edu:kathy): anonymous 331 Guest login ok, use email address as password. Password: ftp> cd /Web/Mosaic/Unix/binaries/2.6 250 CWD command successful. ftp> binary 200 Type set to I. ftp> get Mosaic-hp-2.6.Z Mosaic.Z 200 PORT command successful. 150 Opening BINARY mode data connection for Mosaic-hp-2.6.Z. 226 Transfer complete. local: Mosaic.Z remote: Mosaic-hp-2.6.Z 809343 bytes received in 3.5 seconds (2.3e+02 Kbytes/s) ftp> quit 221 Goodbye. In this example, the user logs into the server ftp.ncsa.edu using the username anonymous and the password kathy@nuts.com, which is her email address. With anonymous FTP, she can log in even though she doesn't have an account on ftp.ncsa.edu. Of course what she can do is restricted, but she can retrieve certain files from the system, and that's just what she does. She changes to the /Web/Mosaic/Unix/binaries/2.6 directory and gets the compressed file Mosaic-hp-2.6.Z. The file is retrieved in binary mode. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_02.htm (1 of 4) [2001-10-15 09:19:03]
  6. [Chapter 13] 13.2 Anonymous FTP 13.2.1 Creating an FTP Server Using the anonymous FTP service offered by a remote server is very simple. However, setting up an anonymous FTP service on your own system is a little more complicated. Here are the steps to set up an anonymous FTP server: 1. Add user ftp to the /etc/passwd file. 2. Create an ftp home directory owned by user ftp that cannot be written to by anyone. 3. Create a bin directory under the ftp home directory that is owned by root, and that cannot be written to by anyone. The ls program should be placed in this directory and changed to mode 111 (execute-only). 4. Create an etc directory in the ftp home directory that is owned by root, and that cannot be written to by anyone. Create special passwd and group files in this directory, and change the mode of both files to 444 (read-only). 5. Create a pub directory in the ftp home directory that is owned by root and is only writable by root, i.e., mode 644. Don't allow remote users to store files on your server, unless it is absolutely necessary and your system is on a private, non-connected network. If you must allow users to store files on the server, change the ownership of this directory to ftp and the mode to 666 (read and write). This should be the only directory where anonymous FTP users can store files. The following examples show each of these steps. First, create the ftp home directory and the required subdirectories. In our example, we create the ftp directory under the /usr directory. # mkdir /usr/ftp # cd /usr/ftp # mkdir bin # mkdir etc # mkdir pub Then copy ls to /usr/ftp/bin, and set the correct permissions. # cp /bin/ls /usr/ftp/bin # chmod 111 /usr/ftp/bin/ls Create a group that will be used only by anonymous FTP, a group that has no other members. In our example we create a group called anonymous. An entry for this new group is added to the /etc/group file, and a file named /usr/ftp/etc/group is created that contains only this single entry. anonymous:*:15: Create a user named ftp by placing an entry for that user in the file /etc/passwd. Also create a file named /usr/ftp/etc/passwd that contains only the ftp entry. Here's the entry we used in both files: Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_02.htm (2 of 4) [2001-10-15 09:19:03]
  7. [Chapter 13] 13.2 Anonymous FTP ftp:*:15:15:Anonymous ftp:/usr/ftp: These examples use a GID of 15 and a UID of 15. These are only examples; pick a UID and GID that aren't used for anything else on your system. A cat of the newly created /usr/ftp/etc/passwd and /usr/ftp/etc/group files shows the following: % cat /usr/ftp/etc/passwd ftp:*:15:15:Anonymous ftp:/usr/ftp: % cat /usr/ftp/etc/group anonymous:*:15: After the edits are complete, set both files to mode 444: # chmod 444 /usr/ftp/etc/passwd # chmod 444 /usr/ftp/etc/group Set the correct ownership and mode for each of the directories. The ownership of /usr/ftp/pub, /usr/ftp/bin, and /usr/ftp/etc do not need to be changed because the directories were created by root. # cd /usr/ftp # chmod 644 pub # chmod 555 bin # chmod 555 etc # cd .. # chown ftp ftp # chmod 555 ftp If you must allow users to write their own files in the pub directory, make the following changes: [2] [2] This opens a large security hole. Allow users to write their own files to the anonymous FTP server only if you must. # chown ftp pub # chmod 666 pub For most UNIX systems, the installation is complete. But if you have a Sun OS 4.x system, a few more steps are necessary. The dynamic linking used by Sun OS requires that the ftp home directory contains: 1. The runtime loader 2. The shared C library 3. /dev/zero Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_02.htm (3 of 4) [2001-10-15 09:19:03]
  8. [Chapter 13] 13.2 Anonymous FTP These Sun-specific steps are shown in the following examples. First, create the directory /usr/ftp/usr/lib, then copy the files ld.so and libc.so.* into the new directory, and set the file permissions: # cd /usr/ftp # mkdir usr # mkdir usr/lib # cp /usr/lib/ld.so usr/lib # cp /usr/lib/libc.so.* usr/lib # chmod 555 libc.so.* # chmod 555 usr/lib # chmod 555 usr Next, create the ftp/dev directory, and run mknod to create dev/zero: # cd /usr/ftp # mkdir dev # cd dev # mknod zero c 3 12 # cd .. # chmod 555 dev Now you can copy the files you wish to make publicly available into /usr/ftp/pub. To prevent these files from being overwritten by remote users, set the mode to 644 and make sure the files are not owned by user ftp. Once you complete the configuration steps necessary for your system, test it thoroughly before announcing the service. Make sure that your server provides the anonymous FTP service you want, without providing additional "services" that you don't want (such as allowing anonymous users access to files outside of the ftp home directory). Anonymous FTP is a potential security risk. If you offer this service at all, limit the number of systems at your site that provide it (one is usually enough), and take care to ensure that the installation is done properly. Previous: 13.1 The World TCP/IP Network Next: 13.3 Finding Files Wide Web Administration 13.1 The World Wide Web Book Index 13.3 Finding Files [ Library Home | DNS & BIND | TCP/IP | sendmail | sendmail Reference | Firewalls | Practical Security ] Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_02.htm (4 of 4) [2001-10-15 09:19:03]
  9. [Chapter 13] 13.3 Finding Files Previous: 13.2 Anonymous Chapter 13 Next: 13.4 Retrieving RFCs Internet Information FTP Resources 13.3 Finding Files Anonymous FTP requires detailed knowledge from the user. To retrieve a file, you must know the FTP server and the directory where the file is located. When the network was small, this was not a major problem. There were a limited number of important FTP servers, and they were well stocked with files. You could always ftp to a major server and search through some directories using ftp's ls command. This old approach is not compatible with a large and expanding Internet for two reasons: q There are now thousands of major anonymous FTP servers. Knowing them all is difficult. q There are now millions of Internet users. They cannot all rely on a few well-known servers. The servers would quickly be overwhelmed with ftp requests. archie is an application designed to help with this problem. It provides a database of information about anonymous FTP sites and the files they contain. 13.3.1 archie archie expands the usefulness of anonymous FTP by helping you locate the file, program, or other information that you need. archie uses information servers that maintain databases containing information about hundreds of FTP servers, and thousands of files and programs throughout the Internet. archie's primary database is a listing of files and the servers from which the files can be retrieved. In the simplest sense, you tell archie which file you're looking for, and archie tells you which FTP servers the file is available from. archie can be used in four different ways: interactively, through electronic mail, via a Web browser, or from an archie client. To use archie interactively, telnet to one of the archie servers. [3] Log in using the username archie and no password. At the archie> prompt, type help to get a full set of interactive archie commands. [3] The list of publicly accessible servers is available at http://www.bunyip.com/products/archie/world/servers.html. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_03.htm (1 of 5) [2001-10-15 09:19:04]
  10. [Chapter 13] 13.3 Finding Files There are many interactive archie commands, but the basic function of locating a program that is accessible via anonymous FTP can be reduced to two commands. prog pattern Display all files in the database with names that match the specified pattern. mail address Mail the output of the last command to address, which is normally your own email address. The following example uses both of these commands to interactively search for gated-R3_5_5.tar, and then mail the results of the search to craig@peanut.nuts.com. % telnet archie.internic.net Trying 198.49.45.10... Connected to archie.ds.internic.net. Escape character is ']'. UNIX(r) System V Release 4.0 (ds0) login: archie # Bunyip Information Systems, Inc., 1993, 1994, 1995 archie> prog gated-R3_5_5.tar # Search type: sub. # Your queue position: 1 # Estimated time for completion: 5 seconds. working... O Host ftp.zcu.cz (147.228.206.16) Last updated 11:32 27 Jun 1997 Location: /pub/security/merit/gated FILE -r--r--r-- 1460773 bytes Jan 1997 gated-R3_5_5.tar.gz archie> mail craig@peanut.nuts.com archie> quit The archie output provides all of the information you need to initiate an anonymous FTP transfer: q The name of the server (ftp.zcu.cz in our example) q The directory on the server that contains the file (/pub/security/merit/gated in our example) q The full name of the file (gated-R3_5_5.tar.gz in our example) You can also use archie by sending email to archie at any one of the archie servers; for example, archie@archie.internic.net. The text of the mail message must contain a valid archie email command. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_03.htm (2 of 5) [2001-10-15 09:19:04]
  11. [Chapter 13] 13.3 Finding Files To get a complete list of archie email commands, send mail containing the help command to one of the servers. In the example below, the email help file is requested from archie.internic.net. % mail archie@archie.internic.net Subject: help ^D EOT While these two methods of accessing archie work fine, the best way to use archie is through a Web browser. Many Web servers provide an archie interface. http://pubweb.nexor.co/uk/public/archie/servers.html lists several of these gateways. The server used in Figure 13.4 is http://archie.bunyip.com/archie.html. Figure 13.4: Archie Web interface Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_03.htm (3 of 5) [2001-10-15 09:19:04]
  12. [Chapter 13] 13.3 Finding Files Enter the name of the program you want to locate in the Search for: box and press the Search button. Your browser displays the search results with links directly to the file you're seeking. For example, assume we rerun the search for gated-R3_5_5.tar.gz using the http://archie.bunyip.com/archie.html Web page. The server returns a list of eight matches, the first of which is the anonymous FTP server at ftp.zcu.cz. The filename gated-R3_5_5.tar.gz that is displayed next to the FTP server is a link. Clicking on the link transfers the file from ftp.zcu.cz to your system. Search and retrieval all in one interface! While the Web browser provides the easiest interface to archie, some people prefer to run an archie client on their local system. Using an archie client reduces the load on the servers and improves responsiveness for the user. If you believe you'll access archie very frequently, it might be worth setting up an archie client. 13.3.1.1 archie client software archie client software is available via anonymous FTP from the ftp.bunyip.com server. The software is stored in the pub/archie/clients directory. The README file in this directory provides a short description of each type of client. There are at least three different client software packages for UNIX: an X windows client and two command-line clients, one written in C and the other written in Perl. Check the archie servers for the latest developments in client software. This section uses the command-line archie client written in C as an example. The C code and the instruction to make the client are all contained in the c-archie-1.4.1.tar.gz file from ftp.bunyip.com. Once the client has been made and installed, it is invoked using the command: % archie [options] string The string is the name of the file that you are asking archie to find. It can be the exact filename, a substring of the name, or a regular expression. The options control how the string is interpreted. The -e option searches for a filename that exactly matches the string; the -s option matches on any record that contains the string as any part of the filename; and the -r option interprets the string as a UNIX regular expression when looking for matches. The following example uses the archie client to search for sites from which the ppp software can be retrieved. The search uses a regular expression that will match any compressed tar file with a name that starts with ppp. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_03.htm (4 of 5) [2001-10-15 09:19:04]
  13. [Chapter 13] 13.3 Finding Files % archie -r '^ppp.*\.tar\.Z' > ppp.locations Our example stores archie's output in the file ppp.locations. You can then examine ppp.locations to find the closest FTP server that has the latest version of the ppp tar file. Redirecting the output to a file is usually a good idea because archie often produces a lot of output. By default, the archie client will return as many as 95 matches to the search. To limit the number of matches returned, use the option -mn, where n is the maximum number of matches archie should return. For example, -m5 limits the search to five matches. The archie database is frequently out-of-date or dominated by obscure FTP servers that have poor connectivity. This limits its utility. But sometimes archie is the only place you have to start your search for a file. Previous: 13.2 Anonymous TCP/IP Network Next: 13.4 Retrieving RFCs FTP Administration 13.2 Anonymous FTP Book Index 13.4 Retrieving RFCs [ Library Home | DNS & BIND | TCP/IP | sendmail | sendmail Reference | Firewalls | Practical Security ] Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_03.htm (5 of 5) [2001-10-15 09:19:04]
  14. [Chapter 13] 13.4 Retrieving RFCs Previous: 13.3 Finding Files Chapter 13 Next: 13.5 Mailing Lists Internet Information Resources 13.4 Retrieving RFCs Throughout this book, we have referred to many RFCs. These are the Internet documents used for everything from general information to the definitions of the TCP/IP protocols standards. As a network administrator, there are several important RFCs that you'll want to read. In this section we describe how you can obtain them. RFCs are available via the World Wide Web at http://www.internic.net. Follow the links from that home page through the directory services to the IETF RFC page. The page allows you to search the RFCs for keywords or to load the RFC index. The index is particularly useful if you know the number of the RFC you want. Figure 13.5 shows a network administrator scrolling through the index looking for RFC 1122. Figure 13.5: The RFC index Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_04.htm (1 of 4) [2001-10-15 09:19:05]
  15. [Chapter 13] 13.4 Retrieving RFCs In another example the network administrator does not know which RFCs contain the information she is looking for, but she knows what she wants. The administrator is trying to find out more about the SMTP service extensions that have been proposed for Extended SMTP. Figure 13.6 shows the four RFCs displayed as a result of her query. Figure 13.6: An RFC Web search Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_04.htm (2 of 4) [2001-10-15 09:19:05]
  16. [Chapter 13] 13.4 Retrieving RFCs The Web provides the most popular and best method for browsing through RFCs. However, if you know what you want, anonymous FTP can be a faster way to retrieve a specific document. RFCs are stored at ds.internic.net in the rfc directory. It stores the RFCs with filenames in the form rfcnnnn.txt or rfcnnnn.ps, where nnnn is the RFC number and txt or ps indicates whether the RFC is ASCII text or PostScript. To retrieve RFC 1122, ftp to ds.internic.net and enter get rfc/rfc1122.txt at the ftp> prompt. This is generally a very quick way to get an RFC, if you know what you want. To help you find out which RFC you do want, get the rfc-index.txt file. It is a complete index of all RFCs by RFC number, and it's available from ds.internic.net in the rfc directory. You'll only need to Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_04.htm (3 of 4) [2001-10-15 09:19:05]
  17. [Chapter 13] 13.4 Retrieving RFCs get a new RFC index occasionally. Most of the time, the RFC you're looking for has been in publication for some time and is already listed in the index. Retrieve the RFC index and store it on your system. Then search it for references to the RFCs you're interested in. 13.4.1 Retrieving RFCs by mail While anonymous FTP is the fastest way and the Web is the best way to get an RFC, they are not the only ways. You can also obtain RFCs through electronic mail. Electronic mail is available to many users who are denied direct access to Internet services because they are on a non-connected network or are sitting behind a restrictive firewall. Also, there are times when email provides sufficient service because you don't need the document quickly. Retrieve RFCs through email by sending mail to mailserv@ds.internic.net. Leave the Subject: line blank. Request the RFC in the body of the email text, preceding the pathname of the RFC with the keyword FILE. In this example, we request RFC 1258. % mail mailserv@ds.internic.net Subject: FILE /rfc/rfc1258.txt ^D The technique works very well. In the time it took to type these paragraphs, the requested RFC was already in my mailbox. Previous: 13.3 Finding Files TCP/IP Network Next: 13.5 Mailing Lists Administration 13.3 Finding Files Book Index 13.5 Mailing Lists [ Library Home | DNS & BIND | TCP/IP | sendmail | sendmail Reference | Firewalls | Practical Security ] Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_04.htm (4 of 4) [2001-10-15 09:19:05]
  18. [Chapter 13] 13.5 Mailing Lists Previous: 13.4 Retrieving Chapter 13 Next: 13.6 The White Pages Internet Information RFCs Resources 13.5 Mailing Lists Mailing lists bring together people with similar interests to exchange information and ideas. Most mailing lists run under usage guidelines that restricted discussion to a specific topic. Mailing lists are often used as places to report problems and get solutions, or to receive announcements. Some mailing lists are digests of newsgroups. There is an enormous number of mailing lists. The list-of-lists contains information about many of the mailing lists that are of interest to network administrators. [4] Use a Web browser to search for mailing lists that interest you at http://catalog.com/vivian/interest-group-search.html. If you prefer, the list-of-lists can be downloaded via anonymous FTP from nisc.sri.com in the file netinfo/interest-groups.txt and searched with standard UNIX tools. Either way, you get the same information. The following example is the list-of-lists entry for the Berkeley Internet Name Domain (BIND) software mailing list: [4] Despite its large size, not every network administration mailing list is contained in the interest-groups.txt file. You hear about some lists by word of mouth. BIND@uunet.uu.net Subscription Address: bind-request@uunet.uu.net Owner: BIND-REQUEST@UUNET.UU.NET Description: This list covers topics relating to Berkeley Internet Name Domain (BIND) domain software. The entry has four sections: the address of the mailing list, the address to which subscription requests are sent, the address of the owner, and a description of the list. When you find a list you wish to join, don't send mail directly to the list asking to be enrolled. Instead, send the enrollment request to the subscription address, which identifies the person or process that maintains the list. If the list is manually maintained, as in the BIND example above, send your enrollment request to list- name-request@host where list-name is the actual name of the list, and is followed by the literal string - request. The -request extension is widely used as the address for administrative requests, such as being added to or dropped from a list, when lists are manually maintained. For example, to join the BIND mailing list, send your enrollment request to bind-request@uunet.uu.net. All other correspondence is sent directly to bind@uunet.uu.net. Many mailing lists automate list management with programs like majordomo and LISTSERV. You can tell Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_05.htm (1 of 5) [2001-10-15 09:19:06]
  19. [Chapter 13] 13.5 Mailing Lists the type of server being used by looking at the subscription address in the list-of-lists. The user portion of that address will be either "majordomo" or "LISTSERV," depending on the server being used. To subscribe to a majordomo list, send email to the subscription address and type the following in the body of the message: subscribe list-address your-address where list-address is the address of the email list, and your-address is your email address. To subscribe to a LISTSERV mailing list, send email to the subscription address with the following in the message body: subscribe list your-name where list is the name of the list, not necessarily its address, as that name appears in the first line of its list- of-lists entry. your-name is your first and last name. This is not your email address. LISTSERV takes your email address from the email headers. 13.5.1 Newsgroups A mailing list is one way of distributing announcements and exchanging questions and answers, but it is not the most efficient way. A mail message is sent to every person on the list. It is sent immediately, and it must be stored on the local system until it is read. Thus, if there are 100 people on a list, 100 messages are sent over the network and stored at 100 receiving systems. Network news provides a more efficient method for distributing this kind of information. The information is stored around the network on, for most sites, one or two news servers. Therefore, instead of moving mail messages to every individual on your network who wants to discuss the Linux operating system, news articles about Linux are stored at one location where they can be read when the user is ready. Not only does this reduce the network load, it reduces the number of redundant copies that are stored on local disk files. Network news is delivered over TCP/IP networks using the Network News Transfer Protocol (NNTP). NNTP is included as part of the TCP/IP protocol stack on most UNIX systems and requires no special configuration. The only thing you need to know to get started is the name of your closest network news server. Ask your ISP. Most ISPs provide network news as part of their basic service. NNTP is a simple command/response protocol. The NNTP server listens to port 119: % telnet news.nuts.com 119 Trying 172.16.16.19... Connected to news.nuts.com. Escape character is ']'. 200 news.nuts.com ready (posting ok). quit 205 Connection closed by foreign host. A help command sent to this server would have produced a list of 23 NNTP commands. Luckily this is not Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_05.htm (2 of 5) [2001-10-15 09:19:06]
  20. [Chapter 13] 13.5 Mailing Lists how you read network news. You use a newsreader. UNIX systems often include a news reader. Our sample Linux system includes several different readers: nn, rn, tin, and trn. Your system may have anyone one of these or another newsreader. See the appropriate manpage for specific instructions on using a particular reader. Regardless of the reader you have, they all have certain things in common. They all provide a way to subscribe to a news group, read articles from the group, and post your own articles to the group. In this trn example from our Linux system, the titles of the first 26 articles in the comp.os.linux.announce group are listed. To read an article, the user scrolls down to select the article and presses Enter. All readers provide a similar interface. comp.os.linux.announce 50 articles (moderated) a root 1 Ringconnect b Clark 1 NTLUG Meeting d Dave 1 Caldera e Martin 1 Linux Users Group Meeting f Evan 1 COMDEX Canada g Jimn 1 Salt Lake Linux Users Group i Tyde 1 San Fransisco Linux users' group j Andy 1 Worcester Linux Users' Group l Bob 1 MELUG meeting o Olaf 1 IP tunnel r Norbert 1 Index files s Albert 1 Client-/Server-Backup t Michael 1 Parallel programming u Oz 1 FTP client v Ted 1 Important notice w Kamran 1 DIPC available x Ken 1 Web site y Cindy 1 CD-ROM available now! z Bishop 1 C program documentation tool -- Select threads (date order) -- Top 38% [>Z] -- Our sample Solaris system doesn't include any news readers mentioned above. But it doesn't matter. News is supported in the Netscape Navigator Web browser. Selecting Netscape News from the Windows menu in the Netscape browser opens a news reader. Figure 13.7 shows us reading news from comp.os.linux. Figure 13.7: Netscape news interface Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. file:///C|/mynapster/Downloads/warez/tcpip/ch13_05.htm (3 of 5) [2001-10-15 09:19:06]
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