388 lines
6.9 KiB
HTML
388 lines
6.9 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Writing hosts and networks Files</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.57"><LINK
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REL="HOME"
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TITLE="Linux Network Administrators Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Configuring TCP/IP Networking"
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HREF="x-087-2-iface.html"><LINK
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REL="PREVIOUS"
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TITLE="Creating Subnets"
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HREF="x-087-2-create.subnets.html"><LINK
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REL="NEXT"
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TITLE="Interface Configuration for IP"
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HREF="x-087-2-iface.interface.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Linux Network Administrators Guide</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="x-087-2-create.subnets.html"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 5. Configuring TCP/IP Networking</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="x-087-2-iface.interface.html"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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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="X-087-2-IFACE.SIMPLE-RESOLV"
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>5.6. Writing hosts and networks Files</A
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></H1
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><P
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>After you have subnetted your network, you should prepare for some simple
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sort of hostname resolution using the <TT
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CLASS="FILENAME"
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>/etc/hosts</TT
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> file.
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If you are not going to use DNS or NIS for address resolution, you have to put
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all hosts in the <TT
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CLASS="FILENAME"
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>hosts</TT
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> file.</P
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><P
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>Even if you want to run DNS or NIS during normal operation, you should
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have some subset of all hostnames in
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<TT
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CLASS="FILENAME"
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>/etc/hosts</TT
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>. You should have some sort of name
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resolution, even when no network interfaces are running, for example,
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during boot time. This is not only a matter of convenience, but it
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allows you to use symbolic hostnames in your network
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<TT
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CLASS="FILENAME"
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>rc</TT
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> scripts. Thus, when changing IP addresses, you
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only have to copy an updated <TT
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CLASS="FILENAME"
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>hosts</TT
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> file to all
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machines and reboot, rather than edit a large number of
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<TT
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CLASS="FILENAME"
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>rc</TT
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> files separately. Usually you put all local
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hostnames and addresses in <TT
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CLASS="FILENAME"
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>hosts</TT
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>, adding those of
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any gateways and NIS servers used.<A
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NAME="X-087-2-FNTC03"
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HREF="#FTN.X-087-2-FNTC03"
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>[1]</A
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></P
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><P
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>You should make sure your resolver only uses information from the
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<TT
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CLASS="FILENAME"
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>hosts</TT
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> file during initial testing. Sample files
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that come with your DNS or NIS software may produce strange
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results. To make all applications use <TT
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CLASS="FILENAME"
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>/etc/hosts</TT
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>
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exclusively when looking up the IP address of a host, you have to edit
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the <TT
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CLASS="FILENAME"
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>/etc/host.conf</TT
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> file. Comment out any lines
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that begin with the keyword <SPAN
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CLASS="SYSTEMITEM"
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>order</SPAN
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> by preceding them with a hash sign,
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and insert the line:
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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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>order hosts</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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>The configuration of the resolver library is covered in detail in
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<A
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HREF="x-087-2-resolv.html"
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>Chapter 6</A
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>.</P
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><P
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>The <TT
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CLASS="FILENAME"
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>hosts</TT
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> file contains one entry per line, consisting
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of an IP address, a hostname, and an optional list of aliases for the
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hostname. The fields are separated by spaces or tabs, and the address
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field must begin in the first column. Anything following a hash sign (#) is
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regarded as a comment and is ignored.</P
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><P
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>Hostnames can be either fully qualified or relative to the local domain.
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For <SPAN
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CLASS="SYSTEMITEM"
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>vale</SPAN
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>, you would usually enter the
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fully qualified name, <SPAN
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CLASS="SYSTEMITEM"
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>vale.vbrew.com</SPAN
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>,
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and <SPAN
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CLASS="SYSTEMITEM"
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>vale</SPAN
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> by itself in the
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<TT
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CLASS="FILENAME"
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>hosts</TT
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> file, so that it is known by both its official name
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and the shorter local name.</P
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><P
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>This is an example how a <TT
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CLASS="FILENAME"
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>hosts</TT
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> file at the Virtual
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Brewery might look. Two special names are included,
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<SPAN
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CLASS="SYSTEMITEM"
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>vlager-if1</SPAN
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> and
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<SPAN
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CLASS="SYSTEMITEM"
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>vlager-if2</SPAN
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>, which give the addresses
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for both interfaces used on <SPAN
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CLASS="SYSTEMITEM"
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>vlager</SPAN
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>:</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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>#
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# Hosts file for Virtual Brewery/Virtual Winery
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#
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# IP FQDN aliases
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#
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127.0.0.1 localhost
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#
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172.16.1.1 vlager.vbrew.com vlager vlager-if1
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172.16.1.2 vstout.vbrew.com vstout
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172.16.1.3 vale.vbrew.com vale
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#
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172.16.2.1 vlager-if2
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172.16.2.2 vbeaujolais.vbrew.com vbeaujolais
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172.16.2.3 vbardolino.vbrew.com vbardolino
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172.16.2.4 vchianti.vbrew.com vchianti</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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>
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Just as with a host's IP address, you should sometimes use a symbolic
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name for network numbers, too. Therefore, the
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<TT
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CLASS="FILENAME"
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>hosts</TT
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> file has a companion called
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<TT
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CLASS="FILENAME"
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>/etc/networks</TT
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> that maps network names to network
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numbers, and vice versa. At the Virtual Brewery, we might install a
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<TT
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CLASS="FILENAME"
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>networks</TT
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> file like this:<A
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NAME="X-087-2-FNTC04"
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HREF="#FTN.X-087-2-FNTC04"
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>[2]</A
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>
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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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># /etc/networks for the Virtual Brewery
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brew-net 172.16.1.0
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wine-net 172.16.2.0</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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></DIV
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><H3
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CLASS="FOOTNOTES"
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>Notes</H3
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><TABLE
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BORDER="0"
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CLASS="FOOTNOTES"
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WIDTH="100%"
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="5%"
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><A
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NAME="FTN.X-087-2-FNTC03"
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HREF="x-087-2-iface.simple-resolv.html#X-087-2-FNTC03"
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>[1]</A
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="95%"
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><P
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>You need the address of an NIS server only if you use Peter Eriksson's
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NYS. Other NIS implementations locate their servers only at runtime by
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using <B
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CLASS="COMMAND"
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>ypbind</B
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>.</P
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></TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="5%"
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><A
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NAME="FTN.X-087-2-FNTC04"
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HREF="x-087-2-iface.simple-resolv.html#X-087-2-FNTC04"
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>[2]</A
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="95%"
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><P
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> Note that names in
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<TT
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CLASS="FILENAME"
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>networks</TT
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> must not collide with hostnames from the
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<TT
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CLASS="FILENAME"
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>hosts</TT
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> file, or else some programs may produce
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strange results.</P
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></TD
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></TR
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></TABLE
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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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WIDTH="100%"
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CELLSPACING="0"
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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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><A
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HREF="x-087-2-create.subnets.html"
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>Prev</A
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></TD
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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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>Next</A
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WIDTH="33%"
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VALIGN="top"
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>Creating Subnets</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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><A
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HREF="x-087-2-iface.html"
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>Up</A
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Interface Configuration for IP</TD
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