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<TITLE>The Answer Guy 44: IP forwarding and Linux</TITLE>
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<H4>"The Linux Gazette...<I>making Linux just a little more fun!</I>"</H4>
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<H1><A NAME="answer">
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<font color="#B03060">The Answer Guy</font>
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<H4>By James T. Dennis,
<a href="mailto:linux-questions-only@ssc.com">linux-questions-only@ssc.com</a><BR>
LinuxCare,
<A HREF="http://www.linuxcare.com/">http://www.linuxcare.com/</A>
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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
height="50" width="60" alt="(?) " border="0"
>IP forwarding and Linux</H3>
<p><strong>From Hal Pomeranz on Mon, 26 Jul 1999
</strong></p>
<P><STRONG>
Jim--
</STRONG></P>
<P><STRONG>
I admit that I'm being lazy and not searching for the answer in a FAQ,
but could you tell me the right incantation under Linux to disable IP
forwarding on multi-homed machines. Thanks muchly in advance!
</STRONG></P>
<P><STRONG>
--Hal
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
It's already the default setting for most Linux kernels.
However, you can force it with:
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><code>
echo 0 &gt; /proc/sys/net/ipv4/ip_forward
</code></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
(you can 'cat' the contents of that node to view the
current setting). It's more commonly necessary to use:
</BLOCKQUOTE>
<BLOCKQUOTE><BlockQuote><code>
echo 1 &gt; /proc/sys/net/ipv4/ip_forward
</code></BlockQuote></BLOCKQUOTE>
<BLOCKQUOTE>
... to ENABLE the forwarding.
</BLOCKQUOTE>
<BLOCKQUOTE>
Of course this assumes that you have <TT>/proc</TT> enabled
in your Linux kernel (also the default and STRONGLY
recommended). I believe there's also a <tt>sysctl()</tt>
interface to this, in case you've stubbornly built
your system without <TT>/proc</TT> support (and replaced the
entire procps suite of utilities including your 'ps'
command).
</BLOCKQUOTE>
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<H5 align="center"><a href="http://www.linuxgazette.com/copying.html"
>Copyright &copy;</a> 1999, James T. Dennis
<BR>Published in <I>The Linux Gazette</I> Issue 44 August 1999</H5>
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