Table of Contents for
Linux Network Administrator's Guide, Second Edition

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Linux Network Administrator's Guide, Second Edition by Terry Dawson Published by O'Reilly Media, Inc., 2000
  1. Cover
  2. Linux Network Administrator’s Guide, 2nd Edition
  3. Preface
  4. Sources of Information
  5. File System Standards
  6. Standard Linux Base
  7. About This Book
  8. The Official Printed Version
  9. Overview
  10. Conventions Used in This Book
  11. Submitting Changes
  12. Acknowledgments
  13. 1. Introduction to Networking
  14. TCP/IP Networks
  15. UUCP Networks
  16. Linux Networking
  17. Maintaining Your System
  18. 2. Issues of TCP/IP Networking
  19. IP Addresses
  20. Address Resolution
  21. IP Routing
  22. The Internet Control Message Protocol
  23. Resolving Host Names
  24. 3. Configuring the Networking Hardware
  25. A Tour of Linux Network Devices
  26. Ethernet Installation
  27. The PLIP Driver
  28. The PPP and SLIP Drivers
  29. Other Network Types
  30. 4. Configuring the Serial Hardware
  31. Introduction to Serial Devices
  32. Accessing Serial Devices
  33. Serial Hardware
  34. Using the Configuration Utilities
  35. Serial Devices and the login: Prompt
  36. 5. Configuring TCP/IP Networking
  37. Installing the Binaries
  38. Setting the Hostname
  39. Assigning IP Addresses
  40. Creating Subnets
  41. Writing hosts and networks Files
  42. Interface Configuration for IP
  43. All About ifconfig
  44. The netstat Command
  45. Checking the ARP Tables
  46. 6. Name Service and Resolver Configuration
  47. How DNS Works
  48. Running named
  49. 7. Serial Line IP
  50. SLIP Operation
  51. Dealing with Private IP Networks
  52. Using dip
  53. Running in Server Mode
  54. 8. The Point-to-Point Protocol
  55. Running pppd
  56. Using Options Files
  57. Using chat to Automate Dialing
  58. IP Configuration Options
  59. Link Control Options
  60. General Security Considerations
  61. Authentication with PPP
  62. Debugging Your PPP Setup
  63. More Advanced PPP Configurations
  64. 9. TCP/IP Firewall
  65. What Is a Firewall?
  66. What Is IP Filtering?
  67. Setting Up Linux for Firewalling
  68. Three Ways We Can Do Filtering
  69. Original IP Firewall (2.0 Kernels)
  70. IP Firewall Chains (2.2 Kernels)
  71. Netfilter and IP Tables (2.4 Kernels)
  72. TOS Bit Manipulation
  73. Testing a Firewall Configuration
  74. A Sample Firewall Configuration
  75. 10. IP Accounting
  76. Configuring IP Accounting
  77. Using IP Accounting Results
  78. Resetting the Counters
  79. Flushing the Ruleset
  80. Passive Collection of Accounting Data
  81. 11. IP Masquerade and Network Address Translation
  82. Configuring the Kernel for IP Masquerade
  83. Configuring IP Masquerade
  84. Handling Name Server Lookups
  85. More About Network Address Translation
  86. 12. Important Network Features
  87. The tcpd Access Control Facility
  88. The Services and Protocols Files
  89. Remote Procedure Call
  90. Configuring Remote Login and Execution
  91. 13. The Network Information System
  92. NIS Versus NIS+
  93. The Client Side of NIS
  94. Running an NIS Server
  95. NIS Server Security
  96. Setting Up an NIS Client with GNU libc
  97. Choosing the Right Maps
  98. Using the passwd and group Maps
  99. Using NIS with Shadow Support
  100. 14. The Network File System
  101. Mounting an NFS Volume
  102. The NFS Daemons
  103. The exports File
  104. Kernel-Based NFSv2 Server Support
  105. Kernel-Based NFSv3 Server Support
  106. 15. IPX and the NCP Filesystem
  107. IPX and Linux
  108. Configuring the Kernel for IPX and NCPFS
  109. Configuring IPX Interfaces
  110. Configuring an IPX Router
  111. Mounting a Remote NetWare Volume
  112. Exploring Some of the Other IPX Tools
  113. Printing to a NetWare Print Queue
  114. NetWare Server Emulation
  115. 16. Managing Taylor UUCP
  116. UUCP Configuration Files
  117. Controlling Access to UUCP Features
  118. Setting Up Your System for Dialing In
  119. UUCP Low-Level Protocols
  120. Troubleshooting
  121. Log Files and Debugging
  122. 17. Electronic Mail
  123. How Is Mail Delivered?
  124. Email Addresses
  125. How Does Mail Routing Work?
  126. Configuring elm
  127. 18. Sendmail
  128. Installing sendmail
  129. Overview of Configuration Files
  130. The sendmail.cf and sendmail.mc Files
  131. Generating the sendmail.cf File
  132. Interpreting and Writing Rewrite Rules
  133. Configuring sendmail Options
  134. Some Useful sendmail Configurations
  135. Testing Your Configuration
  136. Running sendmail
  137. Tips and Tricks
  138. 19. Getting Exim Up and Running
  139. If Your Mail Doesn’t Get Through
  140. Compiling Exim
  141. Mail Delivery Modes
  142. Miscellaneous config Options
  143. Message Routing and Delivery
  144. Protecting Against Mail Spam
  145. UUCP Setup
  146. 20. Netnews
  147. What Is Usenet, Anyway?
  148. How Does Usenet Handle News?
  149. 21. C News
  150. Installation
  151. The sys File
  152. The active File
  153. Article Batching
  154. Expiring News
  155. Miscellaneous Files
  156. Control Messages
  157. C News in an NFS Environment
  158. Maintenance Tools and Tasks
  159. 22. NNTP and the nntpd Daemon
  160. Installing the NNTP Server
  161. Restricting NNTP Access
  162. NNTP Authorization
  163. nntpd Interaction with C News
  164. 23. Internet News
  165. Newsreaders and INN
  166. Installing INN
  167. Configuring INN: the Basic Setup
  168. INN Configuration Files
  169. Running INN
  170. Managing INN: The ctlinnd Command
  171. 24. Newsreader Configuration
  172. trn Configuration
  173. nn Configuration
  174. A. Example Network: The Virtual Brewery
  175. B. Useful Cable Configurations
  176. A Serial NULL Modem Cable
  177. C. Linux Network Administrator’s Guide, Second Edition Copyright Information
  178. 1. Applicability and Definitions
  179. 2. Verbatim Copying
  180. 3. Copying in Quantity
  181. 4. Modifications
  182. 5. Combining Documents
  183. 6. Collections of Documents
  184. 7. Aggregation with Independent Works
  185. 8. Translation
  186. 9. Termination
  187. 10. Future Revisions of this License
  188. D. SAGE: The System Administrators Guild
  189. Index
  190. Colophon

The sys File

The sys file, located in /etc/news, controls which hierarchies you receive and forward to other sites. Although there are maintenance tools named addfeed and delfeed, we think it’s better to maintain this file by hand.

The sys file contains entries for each site to which you forward news, as well as a description of the groups you will accept. The first line is a ME entry that describes your system. It’s a safe bet to use the following:

ME:all/all::

You also have to add a line for each site to which you feed news. Each line looks like this:

               site[/exclusions]:grouplist[/distlist][:flags[:cmds]]

Entries may be continued across newlines using a backslash (\) at the end of the line to be continued. A hash sign (#) denotes a comment.

site

This is the name of the site the entry applies to. One usually chooses the site’s UUCP name for this. There has to be an entry for your site in the sys file too, or you will not receive any articles yourself.

The special site name ME denotes your site. The ME entry defines all groups you are willing to store locally. Articles that aren’t matched by the ME line will go to the junk group.

C News rejects any articles that have already passed through this site to prevent loops. C News does this by ensuring that the local site name does not appear in the Path: of the article. Some sites may be known by a number of valid names. For example, some sites use their fully qualified domain name in this field, or an alias like news. site.domain. To ensure the loop prevention mechanism works, it is important to add all aliases to the exclusion list, separating them by commas.

For the entry applying to site moria, for instance, the site field would contain moria/moria.orcnet.org. If moria were also by an alias of news.orcnet.org, then our site field would contain moria/moria.orcnet.org,news.orcnet.org.

grouplist

This is a comma-separated subscription list of groups and hierarchies for this particular site. A hierarchy may be specified by giving the hierarchy’s prefix (such as comp.os for all groups whose names start with this prefix), optionally followed by the keyword all (e.g., comp.os.all).

You can exclude a hierarchy or group from forwarding by preceding it with an exclamation mark. If a newsgroup is checked against the list, the longest match applies. For example, if grouplist contains this list:

!comp,comp.os.linux,comp.folklore.computers

no groups from the comp hierarchy except comp.folklore.computers and all groups below comp.os.linux will be fed to that site.

If the site requests to be forwarded all news you receive yourself, enter all as grouplist.

distlist

This value is offset from the grouplist by a slash and contains a list of distributions to be forwarded. Again, you may exclude certain distributions by preceding them with an exclamation mark. All distributions are denoted by all. Omitting distlist implies a list of all.

For example, you may use a distribution list of all,!local to prevent news meant only for local use from being sent to remote sites.

There are usually at least two distributions: world, which is often the default distribution used when none is specified by the user, and local. There may be other distributions that apply to a certain region, state, country, etc. Finally, there are two distributions used by C News only; these are sendme and ihave, and are used for the sendme/ihave protocol.

The use of distributions is a subject of debate. The distribution field in a news article can be created arbitrarily, but for a distribution to be effective, the news servers in the network must know it. Some misbehaving newsreaders create bogus distributions by simply assuming the top-level newsgroup hierarchy of the article destination is a reasonable distribution. For example, one might assume comp to be a reasonable distribution to use when posting to the comp.os.linux.networking newsgroup. Distributions that apply to regions are often questionable, too, because news may travel outside of your region when sent across the Internet.[127] Distributions applying to an organization, however, are very meaningful; e.g., to prevent confidential information from leaving the company network. This purpose, however, is generally served better by creating a separate newsgroup or hierarchy.

flags

This option describes certain parameters for the feed. It may be empty or a combination of the following:

F

This flag enables batching.

f

This is almost identical to the F flag, but allows C News to calculate the size of outgoing batches more precisely, and should probably be used in preference.

I

This flag makes C News produce an article list suitable for use by ihave/sendme. Additional modifications to the sys and the batchparms file are required to enable ihave/sendme.

n

This creates batch files for active NNTP transfer clients like nntpxmit (see Chapter 22). The batch files contain the article’s filename along with its message ID.

L

This tells C News to transmit only articles posted at your site. This flag may be followed by a decimal number n, which makes C News transfer articles posted only within n hops from your site. C News determines the number of hops from the Path: field.

u

This tells C News to batch only articles from unmoderated groups.

m

This tells C News to batch only articles from moderated groups.

You may use at most one of F, f, I, or n.

cmds

This field contains a command that will be executed for each article, unless you enable batching. The article will be fed to the command on standard input. This should be used for very small feed only; otherwise, the load on both systems will be too high.

The default command is:

uux - -r -z remote-system!rnews

This invokes rnews on the remote system, feeding it the article on standard input.

The default search path for commands given in this field is /bin:/usr/bin:/usr/lib/news/batch. The latter directory contains a number of shell scripts whose names start with via; they are briefly described later in this chapter.

If batching is enabled using one of the F, f, I, or n flags, C News expects to find a filename in this field rather than a command. If the filename does not begin with a slash (/), it is assumed to be relative to /var/spool/news/out.going. If the field is empty, it defaults to remote-system/togo. The file is expected to be in the same format as the remote-system/togo file and contain a list of articles to transmit.

When setting up C News, you will most probably have to write your own sys file. Here is a sample file for vbrew.com, from which you may copy what you need:

# We take whatever they give us.
ME:all/all::
# We send everything we receive to moria, except for local and
# brewery-related articles. We use batching.
moria/moria.orcnet.org:all,!to,to.moria/all,!local,!brewery:f:
# We mail comp.risks to jack@ponderosa.uucp
ponderosa:comp.risks/all::rmail jack@ponderosa.uucp
# swim gets a minor feed
swim/swim.twobirds.com:comp.os.linux,rec.humor.oracle/all,!local:f:
# Log mail map articles for later processing
usenet-maps:comp.mail.maps/all:F:/var/spool/uumaps/work/batch


[127] It is not uncommon for an article posted in say, Hamburg, to go to Frankfurt via reston.ans.net in the Netherlands, or even via some site in the U.S.