246 lines
4.2 KiB
HTML
246 lines
4.2 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Refuse responding to broadcasts request</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.60"><LINK
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TITLE="Securing and Optimizing Linux"
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TITLE="General System Security"
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HREF="gen-syssecured.html"><LINK
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TITLE="
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The kernel tunable parameters"
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HREF="chap5sec53.html"><LINK
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TITLE="Routing Protocols"
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>Securing and Optimizing Linux: RedHat Edition -A Hands on Guide</TH
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></TR
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WIDTH="10%"
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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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VALIGN="bottom"
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>Chapter 5. General System Security</TD
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><TD
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WIDTH="10%"
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CLASS="section"
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><H1
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CLASS="section"
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><A
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NAME="AEN4050"
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>5.25. Refuse responding to broadcasts request</A
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></H1
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><P
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> As for the ping request, it's also important to disable broadcast request. When a packet is sent to an <SPAN
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CLASS="acronym"
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>IP</SPAN
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> broadcast address (i.e. 192.168.1.255) from a machine on the
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local network, that packet is delivered to all machines on that network. Then all the machines on a network respond to this ICMP echo request and the result can be
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severe network congestion or outages <EM
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>-denial-of-service</EM
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> attacks. See the <SPAN
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CLASS="acronym"
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>RFC</SPAN
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> 2644 for more information.
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<DIV
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CLASS="mediaobject"
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SRC="images/Version6.1.gif"
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ALT="Version 6.1 only"
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></DIV
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>
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<TABLE
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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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> [root@deep] /# <B
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CLASS="command"
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>echo</B
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> 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
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</PRE
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></TD
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></TR
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></TABLE
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>
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You can add this line in your <TT
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CLASS="filename"
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>/etc/rc.d/rc.local</TT
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> file so the command will be automatically set
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if your system reboots.
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</P
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><P
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> <DIV
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CLASS="mediaobject"
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><P
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><IMG
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SRC="images/Version6.2.gif"
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ALT="Version 6.2 only"
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></IMG
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></P
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></DIV
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>
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Edit the <TT
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CLASS="filename"
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>/etc/sysctl.conf</TT
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> file and add the following 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="programlisting"
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> # Enable ignoring broadcasts request
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net.ipv4.icmp_echo_ignore_broadcasts = 1
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</PRE
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></TD
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></TR
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></TABLE
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>
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You must restart your network for the change to take effect. The command to restart the network is the following:
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</P
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><P
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> To restart all networks devices manually on your system, use the following command:
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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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> [root@deep] /# /etc/rc.d/init.d/network <B
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CLASS="command"
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>restart</B
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>
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</PRE
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></TD
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></TR
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></TABLE
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>
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<P
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CLASS="literallayout"
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><TT
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CLASS="computeroutput"
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> Setting network parameters [ OK ]
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Bringing up interface lo [ OK ]
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Bringing up interface eth0 [ OK ]
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Bringing up interface eth1 [ OK ]
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</TT
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></P
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>
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</P
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></DIV
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>The kernel tunable parameters</TD
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><TD
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WIDTH="34%"
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>Routing Protocols</TD
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> |