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    1 The unique fully-qualified domain name
    2     This document will introduce you to the Message-ID and FQDN difficulties
    3     and help you out.
    4 
    5 What is this fully-qualified domain name or FQDN?
    6     The unique fully-qualified domain name (or host name, FQDN or FQHN for
    7     short) is used by leafnode to generate the Message-ID.
    8 
    9     What is the Message-ID?
   10 
   11     Every message (mail or news) has a unique piece of text in its header,
   12     the so-called Message-ID. It is not usually visible in your software
   13     unless you choose "display all headers" or "display raw" or "display
   14     source".
   15 
   16     The Message-ID looks roughly like a strange E-Mail address,
   17     <12345.67890@host.example.com>: it has two parts. Left of the @ is the
   18     "local" part, right of the "@" is the domain part. The local part of the
   19     Message-ID is different for different pieces of mail or news, while the
   20     domain part of the mail address is constant. The domain part is usually
   21     the name of the host that generated the Message-ID: your computer's name
   22     when you are sending mail or posting news.
   23 
   24     Whenever a news server is offered a new news article for redistribution,
   25     it looks at the Message-ID to determine if it already has the article,
   26     to avoid double work, and to avoid that new articles run in circles.
   27 
   28     Therefore, each message sent, mail or news, must have a unique
   29     Message-ID. If the Message-ID is not unique, because you use the same
   30     host name as somebody else, and you and the other person write an
   31     article at the same time, the article that arrives later will be
   32     considered a *duplicate* or *Message-ID collision* and be discarded by
   33     the server - and as messages take a few seconds from one end of the
   34     world to another, two servers at different ends of the net may see the
   35     messages arrive in reverse order.
   36 
   37     Leafnode will tell you that the Message-ID of the article it is about to
   38     post is already in use upstream.
   39 
   40     Please note that this problem is not leafnode-specific. Any mail or news
   41     software may suffer from collisions, but it's less prominent in mail,
   42     and it's difficult to see at all, because the messages disappear
   43     silently, no message will be coming back to tell you another message was
   44     lost.
   45 
   46 How to get a unique fully-qualified domain name
   47     There are several ways to obtain one. When you got yours, see below on
   48     how to configure your domain name.
   49 
   50     If you have a domain registered:
   51         Assume you are the rightful owner of example.com. You can now
   52         reserve any sub domain you wish, say mid.example.com, and a host
   53         name for your leafnode computer, say, abacus.mid.example.com, or for
   54         a friend. How you track that only one machine has the same name at
   55         the same time, is up to you. Writing *gave abacus.mid.example.com to
   56         Joe at 2002-07-11* on a sheet of paper is sufficient - if you can
   57         find this sheet later on.
   58 
   59         Again: This host name need not be entered into your DNS data base,
   60         just make sure only one computer uses this name at the same time.
   61 
   62     If you have an account at "news.individual.de" or "news.individual.net":
   63         You have been assigned a user ID. To find it out, type in your
   64         shell:
   65 
   66          telnet news.individual.de 119
   67 
   68         (wait until connected)
   69 
   70          authinfo user sixpack
   71          authinfo pass joe
   72          quit
   73 
   74         Replace "sixpack" and "joe" by your login and password. After the
   75         "authinfo pass" line, you should see a line that reads:
   76 
   77          281 Authentication accepted. (UID=00000)
   78 
   79         If you get a 481 line, please retry, you may have mistyped user name
   80         or password. Correcting these lines with Backspace or Delete may
   81         also lead to failed logins. Retry with careful typing so that you do
   82         not need to correct your input.
   83 
   84         The server would have printed your user ID where my example shows
   85         00000.
   86 
   87         Your hostname then is ID-00000.user.uni-berlin.de. DO MAKE SURE TO
   88         REPLACE THE NUMBER IN ID-00000 by the number the server told you in
   89         the UID= LINE.
   90 
   91     Specific providers:
   92 
   93         T-Online
   94             T-Online customers, your hostname is NNNNN.dialin.t-online.de,
   95             where NNNNN is your T-Online number. If your T-Online number
   96             contains your telephone number, contact T-Online support to have
   97             a new T-Online number assigned. I'm unaware if they charge you
   98             for this change.
   99 
  100     Ask your network administrator or your Internet service provider.
  101         Your local network administrator can assign you a domain to use for
  102         Message-IDs.
  103 
  104         Your Internet service provider may have reserved a special sub
  105         domain for the sole purpose of letting users create their own unique
  106         Message-IDs.
  107 
  108   When leafnode ignores your host name
  109     Well, it is probably the default name or domain that your OS vendor
  110     chose, like "localhost.localdomain". As such, it is not unique, but used
  111     on many computers, and can therefore cause collisions and in severe
  112     cases make your articles disappear.
  113 
  114   Why localhost.ANYTHING will not work
  115     Many sites run resolvers that are based on ISC Bind code. And many sites
  116     configure their name servers so that they will resolve
  117     localhost.example.com. Therefore, localhost.example.com will not
  118     designate a single computer, but any computer that has "localhost" as a
  119     name. These resolvers are problematic because they will first see the
  120     domain as unqualified and append the domain or searchlist, so assuming
  121     that your domain is example.com, these resolvers will try
  122     localhost.example.com first, which will resolve to 127.0.0.1 at many
  123     sites.
  124 
  125     (It is usually a mistake to add localhost to the name server for a
  126     domain, the clients had better be fixed instead. As a workaround,
  127     removing all domain and searchlist lines from "/etc/resolv.conf" will
  128     usually work at the expense of not being able to use short names unless
  129     they are listed in "/etc/hosts".)
  130 
  131 How to configure the fully-qualified domain name
  132   System-wide
  133     Preferably, the host name is entered into your system configuration so
  134     that it is available globally, to your mailers and news readers should
  135     they desire to create a FQDN.
  136 
  137     How exactly the hostname is configured, depends on your system, it is
  138     usually a two-step approach, but your system installation/configuration
  139     software may simplify things for you.
  140 
  141     1. Configure the bare hostname. Every system has its own favorite
  142     configurator, but you'll find this in the index. SuSE Linux 8.0 and
  143     newer read the hostname from the file "/etc/HOSTNAME". FreeBSD 4 and
  144     newer reads it from the "hostname" variable in "/etc/rc.conf".
  145 
  146     2. On many systems, you will have to put the fully qualified host name
  147     into "/etc/hosts", too, so the system can find out the full name with
  148     domain if given just its bare name without a domain. (On networked
  149     systems, using NIS, DNS or LDAP is also feasible if the client is
  150     configured to use the respective system to resolve host names.) Usually,
  151     a computer that is to resolve a hostname will look at "/etc/hosts" first
  152     and then at DNS.
  153 
  154     An "/etc/hosts" line might look like this:
  155 
  156      192.168.0.1 abacus.mid.example.com abacus oldname
  157 
  158     Keep the original name of the computer as an alias in case you
  159     configured some other software to use the old name.
  160 
  161   Local to leafnode
  162     You can also write a line like
  163 
  164      hostname = abacus.mid.example.com
  165 
  166     into your "/etc/leafnode/config". But I recommend against doing that,
  167     see the next section why:
  168 
  169   Should I configure the FQDN system-wide or local to leafnode?
  170     You should configure the FQDN system-wide. Your news reader may generate
  171     a Message-ID itself, and it is not aware of leafnode's configuration and
  172     will generate an invalid Message-ID -- leafnode will then reject the
  173     posting because the Message-ID is invalid.
  174 
  175 Author, Copyright
  176     This document was written and is (C) Copyright 2002 - 2004, 2006, 2008
  177     by Matthias Andree.
  178 
  179     Permission is hereby granted, free of charge, to any person obtaining a
  180     copy of this software and associated documentation files (the
  181     "Software"), to deal in the Software without restriction, including
  182     without limitation the rights to use, copy, modify, merge, publish,
  183     distribute, sublicense, and/or sell copies of the Software, and to
  184     permit persons to whom the Software is furnished to do so, subject to
  185     the following conditions:
  186 
  187     The above copyright notice and this permission notice shall be included
  188     in all copies or substantial portions of the Software.
  189 
  190     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  191     OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  192     MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  193     IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
  194     CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  195     TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  196     SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  197