267 lines
6.0 KiB
HTML
267 lines
6.0 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Using Internet services with Dynamic IP numbers</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.52"><LINK
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>Linux PPP HOWTO</A
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><H1
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><A
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NAME="DYNAMIC-SERVER"
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>Chapter 23. Using Internet services with Dynamic IP numbers</A
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></H1
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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>23.1. <A
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HREF="dynamic-server.html#AEN1368"
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>Setting up email</A
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></DT
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><DT
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>23.2. <A
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HREF="x1386.html"
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>Setting Up a local Name server</A
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></DT
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></DL
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></DIV
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><P
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>If you are using dynamic IP numbers (and many service providers will only
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give you a dynamic IP number unless you pay significantly more for your
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connection), then you have to recognize the limitations this imposes.</P
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><P
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>First of all, outbound service requests will work just fine. That is,
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you can send email using sendmail (provided you have correctly set up
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sendmail), ftp files from remote sites, finger users on other machines,
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browse the web etc.</P
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><P
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>In particular, you can answer email that you have brought down to your
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machine whilst you are off line. Mail will simply sit in your mail queue
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until you dial back into your ISP.</P
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><P
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>However, your machine is NOT connected to the Internet 24 hours a day,
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nor does it have the same IP number every time it is connected. So it is
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impossible for you to receive email directed to your machine, and very
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difficult to set up a web or ftp server that your friends can access! As
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far as the Internet is concerned your machine does not exist as a
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unique, permanently contactable machine as it does not have a unique IP
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number (remember - other machines will be using the IP number when they
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are allocated it on dial-in).</P
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><P
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>If you set up a WWW, (or any other server), it is totally unknown by any
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user on the Internet UNLESS they know that your machine is connected AND
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its actual (current) IP number. There are a number of ways they can get
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this info, ranging from you ringing them, sending them email to tell
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them or cunning use of ".plan" files on a shell account at your service
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provider (assuming that your provider allows shell and finger access).</P
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><P
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>Now, for most users, this is not a problem - all that most people want
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is to send and receive email (using your account on your service
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provider) and make outbound connections to WWW, ftp and other servers on
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the Internet. If you MUST have inbound connections to your server, you
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should really get a static IP number. Alternatively you can explore the
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methods hinted at above...</P
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="AEN1368"
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>23.1. Setting up email</A
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></H1
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><P
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>Even for dynamic IP numbers, you can certainly configure sendmail on your
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machine to send out any email that you compose locally. Configuration of
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sendmail can be obscure and difficult - so this document does not
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attempt to tell you how to do this. However, you should probably
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configure sendmail so that your Internet service provider is designated
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as your "smart relay" host (the <TT
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CLASS="LITERAL"
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>sendmail.cf</TT
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> <I
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CLASS="EMPHASIS"
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>DS</I
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> option). (For more
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sendmail configuration info, see the sendmail documents - and look at the
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m4 configurations that come with sendmail. There is almost certain to be
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one there that will meet your needs).</P
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><P
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>There are also excellent books on Sendmail (notably the 'bible' from
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O'Reilly and Associates), but these are almost certainly overkill for
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most users!</P
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><P
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>Once you have sendmail configured, you will probably want to have
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sendmail dispatch any messages that have been sitting in the outbound
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mail queue as soon as the PPP connection comes up. To do this, add the
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command</P
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><P
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> <TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>sendmail -q &</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>to your /etc/ppp/ip-up script (see below).</P
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><P
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>Inbound email is a problem for dynamic IP numbers. The way to handle
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this is to:-
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<P
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></P
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><UL
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><LI
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><P
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>configure your mail user agent so that all mail is sent out with a
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"reply to" header giving your email address at your Internet Service
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provider.
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If you can, you should also set your FROM address to be your email
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address at your ISP as well. </P
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></LI
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><LI
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><P
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>use the popclient, fetchmail programs to retrieve your email from your
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service provider. Alternatively, if your ISP is using IMAP, use an IMAP
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enabled mail user agent, (such as pine).</P
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></LI
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></UL
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> </P
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><P
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>You can automate this process at dial up time by putting the necessary
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commands in the <TT
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CLASS="LITERAL"
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>/etc/ppp/ip-up</TT
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> script (see below).</P
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></DIV
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></DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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>Prev</A
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ALIGN="center"
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VALIGN="top"
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HREF="index.html"
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>Home</A
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></TD
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ALIGN="right"
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HREF="x1386.html"
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>Next</A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
|
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ALIGN="left"
|
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VALIGN="top"
|
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>Why can't people finger, WWW, gopher, talk, etc. to my machine?</TD
|
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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> </TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
|
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>Setting Up a local Name server</TD
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> |