320 lines
6.0 KiB
HTML
320 lines
6.0 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Setting up Name to Address Resolution (DNS)</TITLE
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><META
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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="DNS"
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>Chapter 13. Setting up Name to Address Resolution (DNS)</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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>13.1. <A
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HREF="dns.html#AEN877"
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>The <TT
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CLASS="LITERAL"
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>/etc/resolv.conf</TT
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> file</A
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></DT
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><DT
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>13.2. <A
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HREF="x892.html"
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>The <TT
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CLASS="LITERAL"
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>/etc/host.conf</TT
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> file</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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>Whilst we humans like to give names to things, computers really like
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numbers. On a TCP/IP network (which is what the Internet is), we call
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machines by a particular name - and every machine lives in a
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particular domain. For example, my Linux workstation is called
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<I
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CLASS="EMPHASIS"
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>archenland</I
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> and it resides in the <I
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CLASS="EMPHASIS"
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>interweft.com.au</I
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>
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domain. Its human readable address is thus archenland.interweft.com.au (which is known as
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the FQDN - fully qualified domain name).</P
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><P
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>However, for this machine to be found by other computers on the
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Internet, it is actually known by its IP number when computers are
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communicating across the Internet.</P
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><P
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>Translating (resolving) machine (and domain) names into the numbers
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actually used on the Internet is the business of machines that offer the
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Domain Name Service.</P
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><P
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>What happens is this:-</P
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><P
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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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> your machine needs to know the
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IP address of a particular computer. The application requiring this
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information asks the 'resolver' on your Linux PC to provide this
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information; </P
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></LI
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><LI
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><P
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>the resolver queries the local host file (<TT
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CLASS="LITERAL"
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>/etc/hosts</TT
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>
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and/or the domain name servers it knows about (the exact behaviour of
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the resolver is determined by <TT
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CLASS="LITERAL"
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>/etc/host.conf</TT
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>); </P
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></LI
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><LI
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><P
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>if the answer is found in the host file, this answer is returned; </P
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></LI
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><LI
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><P
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>if a domain name server is specified, your PC queries this
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machine; </P
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></LI
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><LI
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><P
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>if the DNS machine already knows the IP number for the required
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name, it returns it. If it does not, it queries other name servers across
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the Internet to find the information. The name server than passes this
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information back to the requesting resolver - which gives the
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information to the requesting application.</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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>When you make a PPP connection, you need to tell your Linux machine
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where it can get host name to IP number (address resolution) information
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so that <I
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CLASS="EMPHASIS"
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>you</I
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> can use the machine names but your <I
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CLASS="EMPHASIS"
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>computer</I
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> can
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translate these to the IP numbers it needs to do its work.</P
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><P
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>One way is to enter every host that you want to talk to into the
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<TT
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CLASS="LITERAL"
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>/etc/hosts</TT
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> file (which is in reality totally impossible if you are
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connecting to the Internet); another is to use the machine IP numbers as
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opposed to the names (an impossible memory task for all but the smallest
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LANs).</P
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><P
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>The best way is to set up Linux so that it knows where to go to get this
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name to number information - automatically. This service is provided by
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the Domain Name Server (DNS) system. All that is necessary is to enter
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the IP number(s) for the domain name servers into your /etc/resolv.conf file.</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="AEN877"
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>13.1. The <TT
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CLASS="LITERAL"
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>/etc/resolv.conf</TT
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> file</A
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></H1
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><P
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>Your PPP server sysadmin/user support people should provide you with two
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DNS IP numbers (only one is necessary - but two gives some
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redundancy in the event of failure).</P
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><P
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>As previously mentioned, Linux cannot set its name server IP number
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in the way that MS Windows 95 does. So you must <I
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CLASS="EMPHASIS"
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>insist</I
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> (politely) that
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your ISP provide you with this information!</P
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><P
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>Your <TT
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CLASS="LITERAL"
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>/etc/resolv.conf</TT
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> should look something like :-</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="PROGRAMLISTING"
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>domain your.isp.domain.name
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nameserver 10.25.0.1
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nameserver 10.25.1.2</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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>Edit this file (creating it if necessary) to represent the information
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that your ISP has provided. It should have ownership and permissions as
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follows :-</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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>-rw-r--r-- 1 root root 73 Feb 19 01:46 /etc/resolv.conf</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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>If you have already set up a <TT
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CLASS="LITERAL"
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>/etc/resolv.conf</TT
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> because you are on a
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LAN, simply add the IP numbers of the PPP DNS servers to your
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existing file.</P
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></DIV
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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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WIDTH="100%"><TABLE
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WIDTH="100%"
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WIDTH="33%"
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><A
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HREF="x808.html"
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>Prev</A
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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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><A
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HREF="index.html"
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>Home</A
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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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><A
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HREF="x892.html"
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>Next</A
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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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>Testing your modem for dial out</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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>The <TT
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CLASS="LITERAL"
|
|
>/etc/host.conf</TT
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> file</TD
|
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |