linux-from-scratch/glfs
1
0
Fork 0
mirror of https://github.com/Zeckmathederg/glfs.git synced 2025-02-04 07:17:15 +08:00
Code Issues Actions Packages Projects Releases Wiki Activity
869a277e9d
glfs/postlfs/security/iptables.xml
Pierre Labastie e1e58be454 Remove all ftp urls 
neither firefox nor epiphany can download them, and they are not
well maintained, because rarely tested.
This is WIP because the "(HTTP)" part of "Download (HTTP)" will
need to be removed too.
But let's see what users think first...
2023-10-15 21:43:08 +02:00

1030 lines
35 KiB
XML
Raw Blame History

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../../general.ent">
%general-entities;
<!ENTITY iptables-download-http "https://www.netfilter.org/projects/iptables/files/iptables-&iptables-version;.tar.xz">
<!ENTITY iptables-download-ftp " ">
<!ENTITY iptables-md5sum "5eaa3bb424dd3a13c98c0cb026314029">
<!ENTITY iptables-size "628 KB">
<!ENTITY iptables-buildsize "16 MB">
<!ENTITY iptables-time "0.1 SBU">
]>
<sect1 id="iptables" xreflabel="iptables-&iptables-version;">
<?dbhtml filename="iptables.html"?>
<title>iptables-&iptables-version;</title>
<indexterm zone="iptables">
<primary sortas="a-iptables">iptables</primary>
</indexterm>
<sect2 role="package">
<title>Introduction to iptables</title>
<para>
<application>iptables</application> is a userspace command line program
used to configure the Linux 2.4 and later kernel packet filtering ruleset.
</para>
&lfs120_checked;
<bridgehead renderas="sect3">Package Information</bridgehead>
<itemizedlist spacing="compact">
<listitem>
<para>
Download (HTTP): <ulink url="&iptables-download-http;"/>
</para>
</listitem>
<listitem>
<para>
Download (FTP): <ulink url="&iptables-download-ftp;"/>
</para>
</listitem>
<listitem>
<para>
Download MD5 sum: &iptables-md5sum;
</para>
</listitem>
<listitem>
<para>
Download size: &iptables-size;
</para>
</listitem>
<listitem>
<para>
Estimated disk space required: &iptables-buildsize;
</para>
</listitem>
<listitem>
<para>
Estimated build time: &iptables-time;
</para>
</listitem>
</itemizedlist>
<bridgehead renderas="sect3">iptables Dependencies</bridgehead>
<bridgehead renderas="sect4">Optional</bridgehead>
<para role="optional">
<!-- <xref linkend="nftables"/>, -->
<xref linkend="libpcap"/> (required for BPF compiler or nfsynproxy support),
<ulink url="https://github.com/tadamdam/bpf-utils">bpf-utils</ulink>
(required for Berkeley Packet Filter support),
<ulink url="https://netfilter.org/projects/libnfnetlink/">libnfnetlink</ulink>
(required for connlabel support),
<ulink url="https://netfilter.org/projects/libnetfilter_conntrack/">libnetfilter_conntrack</ulink>
(required for connlabel support), and
<ulink url="https://netfilter.org/projects/nftables/">nftables</ulink>
</para>
</sect2>
<sect2 role="kernel" id="iptables-kernel">
<title>Kernel Configuration</title>
<para>
A firewall in Linux is accomplished through the netfilter interface. To
use <application>iptables</application> to configure netfilter, the
following kernel configuration parameters are required:
</para>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
href="iptables-kernel.xml"/>
<para>
Include any connection tracking protocols that will be used, as well as
any protocols that you wish to use for match support under the
"Core Netfilter Configuration" section. The above options are enough
for running <xref linkend="fw-persFw-ipt"/> below.
</para>
<indexterm zone="iptables iptables-kernel">
<primary sortas="d-iptables">iptables</primary>
</indexterm>
</sect2>
<sect2 role="installation">
<title>Installation of iptables</title>
<note>
<para>
The installation below does not include building some specialized
extension libraries which require the raw headers in the
<application>Linux</application> source code. If you wish to build the
additional extensions (if you aren't sure, then you probably don't), you
can look at the <filename>INSTALL</filename> file to see an example of
how to change the <parameter>KERNEL_DIR=</parameter> parameter to point
at the <application>Linux</application> source code. Note that if you
upgrade the kernel version, you may also need to recompile
<application>iptables</application> and that the BLFS team has not
tested using the raw kernel headers.
</para>
</note>
<para>
Install <application>iptables</application> by running the following
commands:
</para>
<screen><userinput>./configure --prefix=/usr \
--disable-nftables \
--enable-libipq &amp;&amp;
make</userinput></screen>
<para>
<!-- there is a iptables-test.py script which seems to run a
lot of tests. Unfortunately, success rate is 50% only. Needs
to be clarified how to use and which prerequisites are required
to run to 100%. Contacted Shekhar Sharma for that (Dec'19),
waiting for answer (thomas). -->
This package does not come with a test suite.
</para>
<para>
Now, as the <systemitem class="username">root</systemitem> user:
</para>
<screen role="root"><userinput>make install</userinput></screen>
</sect2>
<sect2 role="commands">
<title>Command Explanations</title>
<para>
<parameter>--disable-nftables</parameter>: This switch disables building
nftables compatibility. <!--Omit this switch if you have installed
<xref linkend="nftables"/>.-->
</para>
<para>
<parameter>--enable-libipq</parameter>: This switch enables building
of <filename class="libraryfile">libipq.so</filename> which
can be used by some packages outside of BLFS.
</para>
<para>
<option>--enable-nfsynproxy</option>: This switch enables installation
of <application>nfsynproxy</application> SYNPROXY configuration tool.
</para>
</sect2>
<sect2 role="configuration">
<title>Configuring iptables</title>
<!--
<note>
<para>
If you intend to use <xref linkend="firewalld"/> to configure your
firewall rules, you should not use the example configurations provided
here, nor should you enable the
<phrase revision="sysv">bootscript.</phrase>
<phrase revision="systemd">systemd unit.</phrase>
</para>
</note>
-->
<note>
<para>
In the following example configurations, <emphasis
role="strong">LAN1</emphasis> is used for the internal LAN interface,
and <emphasis role="strong">WAN1</emphasis> is used for the external
interface connected to the Internet. You will need to replace these
values with appropriate interface names for your system.
</para>
</note>
<sect3 id="fw-persFw-ipt"
xreflabel="Creating a Personal Firewall With iptables">
<title>Personal Firewall</title>
<para>
A Personal Firewall is designed to let you access all the
services offered on the Internet while keeping your computer secure and
your data private.
</para>
<para>
Below is a slightly modified version of Rusty Russell's
recommendation from the <ulink
url="https://www.netfilter.org/documentation/HOWTO/packet-filtering-HOWTO.html">
Linux 2.4 Packet Filtering HOWTO</ulink>. It is still applicable
to the Linux 6.x kernels.
</para>
<screen role="root" revision="sysv"><?dbfo keep-together="auto"?><userinput>cat &gt; /etc/rc.d/rc.iptables &lt;&lt; "EOF"
<literal>#!/bin/sh
# Begin rc.iptables
# Insert connection-tracking modules
# (not needed if built into the kernel)
modprobe nf_conntrack
modprobe xt_LOG
# Enable broadcast echo Protection
echo 1 &gt; /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
# Disable Source Routed Packets
echo 0 &gt; /proc/sys/net/ipv4/conf/all/accept_source_route
echo 0 &gt; /proc/sys/net/ipv4/conf/default/accept_source_route
# Enable TCP SYN Cookie Protection
echo 1 &gt; /proc/sys/net/ipv4/tcp_syncookies
# Disable ICMP Redirect Acceptance
echo 0 &gt; /proc/sys/net/ipv4/conf/default/accept_redirects
# Do not send Redirect Messages
echo 0 &gt; /proc/sys/net/ipv4/conf/all/send_redirects
echo 0 &gt; /proc/sys/net/ipv4/conf/default/send_redirects
# Drop Spoofed Packets coming in on an interface, where responses
# would result in the reply going out a different interface.
echo 1 &gt; /proc/sys/net/ipv4/conf/all/rp_filter
echo 1 &gt; /proc/sys/net/ipv4/conf/default/rp_filter
# Log packets with impossible addresses.
echo 1 &gt; /proc/sys/net/ipv4/conf/all/log_martians
echo 1 &gt; /proc/sys/net/ipv4/conf/default/log_martians
# be verbose on dynamic ip-addresses (not needed in case of static IP)
echo 2 &gt; /proc/sys/net/ipv4/ip_dynaddr
# disable Explicit Congestion Notification
# too many routers are still ignorant
echo 0 &gt; /proc/sys/net/ipv4/tcp_ecn
# Set a known state
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP
# These lines are here in case rules are already in place and the
# script is ever rerun on the fly. We want to remove all rules and
# pre-existing user defined chains before we implement new rules.
iptables -F
iptables -X
iptables -Z
iptables -t nat -F
# Allow local-only connections
iptables -A INPUT -i lo -j ACCEPT
# Free output on any interface to any ip for any service
# (equal to -P ACCEPT)
iptables -A OUTPUT -j ACCEPT
# Permit answers on already established connections
# and permit new connections related to established ones
# (e.g. port mode ftp)
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
# Drop any incoming MULTICAST or BROADCAST packet before logging:
# The box outputs several of them when using netbios or mDNS, and those
# appear immediately as incoming, which clutters the log.
iptables -A INPUT -m addrtype --dst-type BROADCAST,MULTICAST -j DROP
# Log everything else.
iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
# End $rc_base/rc.iptables</literal>
EOF
chmod 700 /etc/rc.d/rc.iptables</userinput></screen>
<screen role="root" revision="systemd"><?dbfo keep-together="auto"?><userinput>install -v -dm755 /etc/systemd/scripts
cat &gt; /etc/systemd/scripts/iptables &lt;&lt; "EOF"
<literal>#!/bin/sh
# Begin /etc/systemd/scripts/iptables
# Insert connection-tracking modules
# (not needed if built into the kernel)
modprobe nf_conntrack
modprobe xt_LOG
# Enable broadcast echo Protection
echo 1 &gt; /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
# Disable Source Routed Packets
echo 0 &gt; /proc/sys/net/ipv4/conf/all/accept_source_route
echo 0 &gt; /proc/sys/net/ipv4/conf/default/accept_source_route
# Enable TCP SYN Cookie Protection
echo 1 &gt; /proc/sys/net/ipv4/tcp_syncookies
# Disable ICMP Redirect Acceptance
echo 0 &gt; /proc/sys/net/ipv4/conf/default/accept_redirects
# Do not send Redirect Messages
echo 0 &gt; /proc/sys/net/ipv4/conf/all/send_redirects
echo 0 &gt; /proc/sys/net/ipv4/conf/default/send_redirects
# Drop Spoofed Packets coming in on an interface, where responses
# would result in the reply going out a different interface.
echo 1 &gt; /proc/sys/net/ipv4/conf/all/rp_filter
echo 1 &gt; /proc/sys/net/ipv4/conf/default/rp_filter
# Log packets with impossible addresses.
echo 1 &gt; /proc/sys/net/ipv4/conf/all/log_martians
echo 1 &gt; /proc/sys/net/ipv4/conf/default/log_martians
# be verbose on dynamic ip-addresses (not needed in case of static IP)
echo 2 &gt; /proc/sys/net/ipv4/ip_dynaddr
# disable Explicit Congestion Notification
# too many routers are still ignorant
echo 0 &gt; /proc/sys/net/ipv4/tcp_ecn
# Set a known state
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP
# These lines are here in case rules are already in place and the
# script is ever rerun on the fly. We want to remove all rules and
# pre-existing user defined chains before we implement new rules.
iptables -F
iptables -X
iptables -Z
iptables -t nat -F
# Allow local-only connections
iptables -A INPUT -i lo -j ACCEPT
# Free output on any interface to any ip for any service
# (equal to -P ACCEPT)
iptables -A OUTPUT -j ACCEPT
# Permit answers on already established connections
# and permit new connections related to established ones
# (e.g. port mode ftp)
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
# Log everything else.
iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
# End /etc/systemd/scripts/iptables</literal>
EOF
chmod 700 /etc/systemd/scripts/iptables</userinput></screen>
<para>
This script is quite simple, it drops all traffic coming
into your computer that wasn't initiated from your computer, but
as long as you are simply surfing the Internet you are unlikely
to exceed its limits.
</para>
<para>
If you frequently encounter certain delays at accessing
FTP servers, take a look at <xref linkend="fw-BB-4-ipt"/>.
</para>
<para>
Even if you have daemons or services running on your system,
these will be inaccessible everywhere but from your computer itself.
If you want to allow access to services on your machine, such as
<command>ssh</command> or <command>ping</command>, take a look at
<xref linkend="fw-busybox-ipt"/>.
</para>
</sect3>
<sect3 id="fw-masqRouter-ipt"
xreflabel="Creating a Masquerading Router With iptables">
<title>Masquerading Router</title>
<para>
A Network Firewall has two interfaces, one connected to an
intranet, in this example <emphasis role="strong">LAN1</emphasis>,
and one connected to the Internet, here <emphasis
role="strong">WAN1</emphasis>. To provide the maximum security
for the firewall itself, make sure that there are no unnecessary
servers running on it such as <application>X11</application>.
As a general principle, the firewall itself should not access
any untrusted service (think of a remote server giving answers that
makes a daemon on your system crash, or even worse, that implements
a worm via a buffer-overflow).
</para>
<screen role="root" revision="sysv"><?dbfo keep-together="auto"?><userinput>cat &gt; /etc/rc.d/rc.iptables &lt;&lt; "EOF"
<literal>#!/bin/sh
# Begin rc.iptables
echo
echo "You're using the example configuration for a setup of a firewall"
echo "from Beyond Linux From Scratch."
echo "This example is far from being complete, it is only meant"
echo "to be a reference."
echo "Firewall security is a complex issue, that exceeds the scope"
echo "of the configuration rules below."
echo "You can find additional information"
echo "about firewalls in Chapter 4 of the BLFS book."
echo "https://www.&lfs-domainname;/blfs"
echo
# Insert iptables modules (not needed if built into the kernel).
modprobe nf_conntrack
modprobe nf_conntrack_ftp
modprobe xt_conntrack
modprobe xt_LOG
modprobe xt_state
# Enable broadcast echo Protection
echo 1 &gt; /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
# Disable Source Routed Packets
echo 0 &gt; /proc/sys/net/ipv4/conf/all/accept_source_route
# Enable TCP SYN Cookie Protection
echo 1 &gt; /proc/sys/net/ipv4/tcp_syncookies
# Disable ICMP Redirect Acceptance
echo 0 &gt; /proc/sys/net/ipv4/conf/all/accept_redirects
# Don't send Redirect Messages
echo 0 &gt; /proc/sys/net/ipv4/conf/default/send_redirects
# Drop Spoofed Packets coming in on an interface where responses
# would result in the reply going out a different interface.
echo 1 &gt; /proc/sys/net/ipv4/conf/default/rp_filter
# Log packets with impossible addresses.
echo 1 &gt; /proc/sys/net/ipv4/conf/all/log_martians
# Be verbose on dynamic ip-addresses (not needed in case of static IP)
echo 2 &gt; /proc/sys/net/ipv4/ip_dynaddr
# Disable Explicit Congestion Notification
# Too many routers are still ignorant
echo 0 &gt; /proc/sys/net/ipv4/tcp_ecn
# Set a known state
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP
# These lines are here in case rules are already in place and the
# script is ever rerun on the fly. We want to remove all rules and
# pre-existing user defined chains before we implement new rules.
iptables -F
iptables -X
iptables -Z
iptables -t nat -F
# Allow local connections
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# Allow forwarding if the initiated on the intranet
iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD ! -i WAN1 -m conntrack --ctstate NEW -j ACCEPT
# Do masquerading
# (not needed if intranet is not using private ip-addresses)
iptables -t nat -A POSTROUTING -o WAN1 -j MASQUERADE
# Log everything for debugging
# (last of all rules, but before policy rules)
iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
iptables -A FORWARD -j LOG --log-prefix "FIREWALL:FORWARD "
iptables -A OUTPUT -j LOG --log-prefix "FIREWALL:OUTPUT "
# Enable IP Forwarding
echo 1 &gt; /proc/sys/net/ipv4/ip_forward</literal>
EOF
chmod 700 /etc/rc.d/rc.iptables</userinput></screen>
<screen role="root" revision="systemd"><?dbfo keep-together="auto"?><userinput>install -v -dm755 /etc/systemd/scripts
cat &gt; /etc/systemd/scripts/iptables &lt;&lt; "EOF"
<literal>#!/bin/sh
# Begin /etc/systemd/scripts/iptables
echo
echo "You're using the example configuration for a setup of a firewall"
echo "from Beyond Linux From Scratch."
echo "This example is far from being complete, it is only meant"
echo "to be a reference."
echo "Firewall security is a complex issue, that exceeds the scope"
echo "of the configuration rules below."
echo "You can find additional information"
echo "about firewalls in Chapter 4 of the BLFS book."
echo "https://www.&lfs-domainname;/blfs"
echo
# Insert iptables modules (not needed if built into the kernel).
modprobe nf_conntrack
modprobe nf_conntrack_ftp
modprobe xt_conntrack
modprobe xt_LOG
modprobe xt_state
# Enable broadcast echo Protection
echo 1 &gt; /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
# Disable Source Routed Packets
echo 0 &gt; /proc/sys/net/ipv4/conf/all/accept_source_route
# Enable TCP SYN Cookie Protection
echo 1 &gt; /proc/sys/net/ipv4/tcp_syncookies
# Disable ICMP Redirect Acceptance
echo 0 &gt; /proc/sys/net/ipv4/conf/all/accept_redirects
# Don't send Redirect Messages
echo 0 &gt; /proc/sys/net/ipv4/conf/default/send_redirects
# Drop Spoofed Packets coming in on an interface where responses
# would result in the reply going out a different interface.
echo 1 &gt; /proc/sys/net/ipv4/conf/default/rp_filter
# Log packets with impossible addresses.
echo 1 &gt; /proc/sys/net/ipv4/conf/all/log_martians
# Be verbose on dynamic ip-addresses (not needed in case of static IP)
echo 2 &gt; /proc/sys/net/ipv4/ip_dynaddr
# Disable Explicit Congestion Notification
# Too many routers are still ignorant
echo 0 &gt; /proc/sys/net/ipv4/tcp_ecn
# Set a known state
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP
# These lines are here in case rules are already in place and the
# script is ever rerun on the fly. We want to remove all rules and
# pre-existing user defined chains before we implement new rules.
iptables -F
iptables -X
iptables -Z
iptables -t nat -F
# Allow local connections
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# Allow forwarding if the initiated on the intranet
iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD ! -i WAN1 -m conntrack --ctstate NEW -j ACCEPT
# Do masquerading
# (not needed if intranet is not using private ip-addresses)
iptables -t nat -A POSTROUTING -o WAN1 -j MASQUERADE
# Log everything for debugging
# (last of all rules, but before policy rules)
iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
iptables -A FORWARD -j LOG --log-prefix "FIREWALL:FORWARD "
iptables -A OUTPUT -j LOG --log-prefix "FIREWALL:OUTPUT "
# Enable IP Forwarding
echo 1 &gt; /proc/sys/net/ipv4/ip_forward
# The following sections allow inbound packets for specific examples
# Uncomment the example lines and adjust as necessary
# Allow ping on the external interface
#iptables -A INPUT -p icmp -m icmp --icmp-type echo-request -j ACCEPT
#iptables -A OUTPUT -p icmp -m icmp --icmp-type echo-reply -j ACCEPT
# Reject ident packets with TCP reset to avoid delays with FTP or IRC
#iptables -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset
# Allow HTTP and HTTPS to 192.168.0.2
#iptables -A PREROUTING -t nat -i WAN1 -p tcp --dport 80 -j DNAT --to 192.168.0.2
#iptables -A PREROUTING -t nat -i WAN1 -p tcp --dport 443 -j DNAT --to 192.168.0.2
#iptables -A FORWARD -p tcp -d 192.168.0.2 --dport 80 -j ACCEPT
#iptables -A FORWARD -p tcp -d 192.168.0.2 --dport 443 -j ACCEPT
# End /etc/systemd/scripts/iptables</literal>
EOF
chmod 700 /etc/systemd/scripts/iptables</userinput></screen>
<para>
With this script your intranet should be reasonably secure
against external attacks. No one should be able to setup a new
connection to any internal service and, if it's masqueraded,
makes your intranet invisible to the Internet. Furthermore, your
firewall should be relatively safe because there are no services
running that a cracker could attack.
</para>
</sect3>
<sect3 id="fw-busybox-ipt" xreflabel="Creating a BusyBox With iptables">
<title>BusyBox</title>
<para>
This scenario isn't too different from the <xref
linkend="fw-masqRouter-ipt"/>, but additionally offers some
services to your intranet. Examples of this can be when
you want to administer your firewall from another host on
your intranet or use it as a proxy or a name server.
</para>
<note>
<para>
Outlining specifically how to protect a server that
offers services on the Internet goes far beyond the scope of
this document. See the references in <xref linkend="fw-extra-info"/>
for more information.
</para>
</note>
<para>
Be cautious. Every service you have enabled makes your
setup more complex and your firewall less secure. You are
exposed to the risks of misconfigured services or running
a service with an exploitable bug. A firewall should generally
not run any extra services. See the introduction to the
<xref linkend="fw-masqRouter-ipt"/> for some more details.
</para>
<para>
If you want to add services such as internal Samba or
name servers that do not need to access the Internet themselves,
the additional statements are quite simple and should still be
acceptable from a security standpoint. Just add the following lines
into the script <emphasis>before</emphasis> the logging rules.
</para>
<screen><literal>iptables -A INPUT -i ! WAN1 -j ACCEPT
iptables -A OUTPUT -o ! WAN1 -j ACCEPT</literal></screen>
<para>
If daemons, such as squid, have to access the Internet
themselves, you could open OUTPUT generally and restrict
INPUT.
</para>
<screen><literal>iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT -j ACCEPT</literal></screen>
<para>
However, it is generally not advisable to leave OUTPUT
unrestricted. You lose any control over trojans who would like
to "call home", and a bit of redundancy in case you've
(mis-)configured a service so that it broadcasts its existence
to the world.
</para>
<para>
To accomplish this, you should restrict INPUT and OUTPUT
on all ports except those that it's absolutely necessary to have
open. Which ports you have to open depends on your needs: mostly
you will find them by looking for failed accesses in your log
files.
</para>
<itemizedlist spacing="compact" role='iptables'>
<title>Have a Look at the Following Examples:</title>
<listitem>
<para>
Squid is caching the web:
</para>
<screen><literal>iptables -A OUTPUT -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -p tcp --sport 80 -m conntrack --ctstate ESTABLISHED \
-j ACCEPT</literal></screen>
</listitem>
<listitem>
<para>
Your caching name server (e.g., named) does its lookups via UDP:
</para>
<screen><literal>iptables -A OUTPUT -p udp --dport 53 -j ACCEPT</literal></screen>
</listitem>
<listitem>
<para>
You want to be able to ping your computer to ensure it's still
alive:
</para>
<screen><literal>iptables -A INPUT -p icmp -m icmp --icmp-type echo-request -j ACCEPT
iptables -A OUTPUT -p icmp -m icmp --icmp-type echo-reply -j ACCEPT</literal></screen>
</listitem>
<listitem>
<para id='fw-BB-4-ipt' xreflabel="BusyBox with iptables example number 4">
If you are frequently accessing FTP servers or enjoy chatting, you
might notice delays because some implementations of these daemons
query an identd daemon on your system to obtain usernames. Although
there's really little harm in this, having an identd running is not
recommended because many security experts feel the service gives
out too much additional information.
</para>
<para>
To avoid these delays you could reject the requests with a
'tcp-reset' response:
</para>
<screen><literal>iptables -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset</literal></screen>
</listitem>
<listitem>
<para>
To log and drop invalid packets (packets
that came in after netfilter's timeout or some types of
network scans) insert these rules at the top of the chain:
</para>
<screen><literal>iptables -I INPUT 0 -p tcp -m conntrack --ctstate INVALID \
-j LOG --log-prefix "FIREWALL:INVALID "
iptables -I INPUT 1 -p tcp -m conntrack --ctstate INVALID -j DROP</literal></screen>
</listitem>
<listitem>
<para>
Anything coming from the outside should not have a
private address, this is a common attack called IP-spoofing:
</para>
<screen><literal>iptables -A INPUT -i WAN1 -s 10.0.0.0/8 -j DROP
iptables -A INPUT -i WAN1 -s 172.16.0.0/12 -j DROP
iptables -A INPUT -i WAN1 -s 192.168.0.0/16 -j DROP</literal></screen>
<para>
There are other addresses that you may also want to drop:
0.0.0.0/8, 127.0.0.0/8, 224.0.0.0/3 (multicast and
experimental), 169.254.0.0/16 (Link Local Networks), and
192.0.2.0/24 (IANA defined test network).
</para>
</listitem>
<listitem>
<para>
If your firewall is a DHCP client, you need to allow those packets:
</para>
<screen><literal>iptables -A INPUT -i WAN1 -p udp -s 0.0.0.0 --sport 67 \
-d 255.255.255.255 --dport 68 -j ACCEPT</literal></screen>
</listitem>
<listitem>
<para>
To simplify debugging and be fair to anyone who'd like
to access a service you have disabled, purposely or by mistake,
you could REJECT those packets that are dropped.
</para>
<para>
Obviously this must be done directly after logging as the very
last lines before the packets are dropped by policy:
</para>
<screen><literal>iptables -A INPUT -j REJECT</literal></screen>
</listitem>
</itemizedlist>
<para>
These are only examples to show you some of the capabilities
of the firewall code in Linux. Have a look at the man page of iptables.
There you will find much more information. The port numbers needed for
this can be found in <filename>/etc/services</filename>, in case you
didn't find them by trial and error in your log file.
</para>
</sect3>
<sect3 id="iptables-init">
<title><phrase revision="sysv">Boot Script</phrase>
<phrase revision="systemd">Systemd Unit</phrase></title>
<para revision="sysv">
To set up the iptables firewall at boot, install the
<filename>/etc/rc.d/init.d/iptables</filename> init script included
in the <xref linkend="bootscripts"/> package.
</para>
<para revision="systemd">
To set up the iptables firewall at boot, install the
<filename>iptables.service</filename> unit included in the
<xref linkend="systemd-units"/> package.
</para>
<indexterm zone="iptables iptables-init">
<primary sortas="f-iptables">iptables</primary>
</indexterm>
<screen role="root"><userinput>make install-iptables</userinput></screen>
</sect3>
</sect2>
<sect2 role="content">
<title>Contents</title>
<segmentedlist>
<segtitle>Installed Programs</segtitle>
<segtitle>Installed Libraries</segtitle>
<segtitle>Installed Directories</segtitle>
<seglistitem>
<seg>
ip6tables,
ip6tables-apply,
ip6tables-legacy,
ip6tables-legacy-restore,
ip6tables-legacy-save,
ip6tables-restore,
ip6tables-save,
iptables,
iptables-apply,
iptables-legacy,
iptables-legacy-restore,
iptables-legacy-apply,
iptables-restore,
iptables-save,
iptables-xml,
nfsynproxy (optional),
and xtables-multi
</seg>
<seg>
libip4tc.so,
libip6tc.so,
libipq.so,
libiptc.so,
and libxtables.so
</seg>
<seg>
/lib/xtables and
/usr/include/libiptc
</seg>
</seglistitem>
</segmentedlist>
<variablelist>
<bridgehead renderas="sect3">Short Descriptions</bridgehead>
<?dbfo list-presentation="list"?>
<?dbhtml list-presentation="table"?>
<varlistentry id="iptables-prog">
<term><command>iptables</command></term>
<listitem>
<para>
is used to set up, maintain, and inspect the tables of
IP packet filter rules in the Linux kernel
</para>
<indexterm zone="iptables iptables-prog">
<primary sortas="b-iptables">iptables</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="iptables-apply">
<term><command>iptables-apply</command></term>
<listitem>
<para>
is a safer way to update iptables remotely
</para>
<indexterm zone="iptables iptables-apply">
<primary sortas="b-iptables-apply">iptables-apply</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="iptables-legacy">
<term><command>iptables-legacy</command></term>
<listitem>
<para>
is used to interact with iptables using the legacy command set
</para>
<indexterm zone="iptables iptables-legacy">
<primary sortas="b-iptables-legacy">iptables-legacy</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="iptables-legacy-restore">
<term><command>iptables-legacy-restore</command></term>
<listitem>
<para>
is used to restore a set of legacy iptables rules
</para>
<indexterm zone="iptables iptables-legacy-restore">
<primary sortas="b-iptables-legacy-restore">iptables-legacy-restore</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="iptables-legacy-save">
<term><command>iptables-legacy-save</command></term>
<listitem>
<para>
is used to save a set of legacy iptables rules
</para>
<indexterm zone="iptables iptables-legacy-save">
<primary sortas="b-iptables-legacy-save">iptables-legacy-save</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="iptables-restore">
<term><command>iptables-restore</command></term>
<listitem>
<para>
is used to restore IP Tables from data specified on
STDIN. Use I/O redirection provided by your
shell to read from a file
</para>
<indexterm zone="iptables iptables-restore">
<primary sortas="b-iptables-restore">iptables-restore</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="iptables-save">
<term><command>iptables-save</command></term>
<listitem>
<para>
is used to dump the contents of an IP Table in easily
parseable format to STDOUT. Use I/O-redirection
provided by your shell to write to a file
</para>
<indexterm zone="iptables iptables-save">
<primary sortas="b-iptables-save">iptables-save</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="iptables-xml">
<term><command>iptables-xml</command></term>
<listitem>
<para>
is used to convert the output of
<command>iptables-save</command> to an XML format. Using the
<filename>iptables.xslt</filename> stylesheet converts the XML
back to the format of <command>iptables-restore</command>
</para>
<indexterm zone="iptables iptables-xml">
<primary sortas="b-iptables-xml">iptables-xml</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="ip6tables">
<term><command>ip6tables*</command></term>
<listitem>
<para>
are a set of commands for IPV6 that parallel the iptables
commands above
</para>
<indexterm zone="iptables ip6tables">
<primary sortas="b-ip6tables">ip6tables</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="nfsynproxy">
<term><command>nfsynproxy</command></term>
<listitem>
<para>
(optional) configuration tool. SYNPROXY target makes handling of
large SYN floods possible without the large performance penalties
imposed by the connection tracking in such cases
</para>
<indexterm zone="iptables nfsynproxy">
<primary sortas="b-nfsynproxy">nfsynproxy</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="xtables-multi">
<term><command>xtables-multi</command></term>
<listitem>
<para>
is a binary that behaves according to the name it is called by
</para>
<indexterm zone="iptables xtables-multi">
<primary sortas="b-xtables-multi">xtables-multi</primary>
</indexterm>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>
Reference in New Issue View Git Blame Copy Permalink