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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.
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.
9 What is the Message-ID?
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
16 The Message-ID looks roughly like a strange E-Mail address,
17 <email@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.
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.
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.
37 Leafnode will tell you that the Message-ID of the article it is about to
38 post is already in use upstream.
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
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.
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.
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.
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
66 telnet news.individual.de 119
68 (wait until connected)
70 authinfo user sixpack
71 authinfo pass joe
74 Replace "sixpack" and "joe" by your login and password. After the
75 "authinfo pass" line, you should see a line that reads:
77 281 Authentication accepted. (UID=00000)
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.
84 The server would have printed your user ID where my example shows
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.
91 Specific providers:
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.
100 Ask your network administrator or your Internet service provider.
101 Your local network administrator can assign you a domain to use for
104 Your Internet service provider may have reserved a special sub
105 domain for the sole purpose of letting users create their own unique
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.
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
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".)
131 How to configure the fully-qualified domain name
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.
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.
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".
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.
154 An "/etc/hosts" line might look like this:
156 192.168.0.1 abacus.mid.example.com abacus oldname
158 Keep the original name of the computer as an alias in case you
159 configured some other software to use the old name.
161 Local to leafnode
162 You can also write a line like
164 hostname = abacus.mid.example.com
166 into your "/etc/leafnode/config". But I recommend against doing that,
167 see the next section why:
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.
175 Author, Copyright
176 This document was written and is (C) Copyright 2002 - 2004, 2006, 2008
177 by Matthias Andree.
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:
187 The above copyright notice and this permission notice shall be included
188 in all copies or substantial portions of the Software.
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.