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214 lines
8.8 KiB
XML
214 lines
8.8 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<refentry>
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<refmeta>
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<refentrytitle>shorewall-nesting</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>nesting</refname>
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<refpurpose>Shorewall Nested Zones</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<arg choice="plain"
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rep="norepeat"><replaceable>child-zone</replaceable>[:<replaceable>parent-zone</replaceable>[,<replaceable>parent-zone</replaceable>]...]</arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>In <ulink url="shorewall-zones.html">shorewall-zones</ulink>(5), a
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zone may be declared to be a sub-zone of one or more other zones using the
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above syntax.</para>
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<para>Where zones are nested, the CONTINUE policy in <ulink
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url="shorewall-policy.html">shorewall-policy</ulink>(5) allows hosts that
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are within multiple zones to be managed under the rules of all of these
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zones.</para>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<para><filename>/etc/shorewall/zones</filename>:</para>
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<programlisting> #ZONE TYPE OPTION
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fw firewall
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net ipv4
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sam:net ipv4
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loc ipv4</programlisting>
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<para><filename>/etc/shorewall/interfaces</filename>:</para>
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<programlisting> #ZONE INTERFACE BROADCAST OPTIONS
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- eth0 detect dhcp,norfc1918
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loc eth1 detect</programlisting>
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<para><filename>/etc/shorewall/hosts</filename>:</para>
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<programlisting> #ZONE HOST(S) OPTIONS
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net eth0:0.0.0.0/0
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sam eth0:206.191.149.197</programlisting>
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<para><filename>/etc/shorewall/policy</filename>:</para>
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<programlisting> #SOURCE DEST POLICY LOG LEVEL
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loc net ACCEPT
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sam all CONTINUE
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net all DROP info
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all all REJECT info</programlisting>
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<para>The second entry above says that when Sam is the client, connection
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requests should first be processed under rules where the source zone is
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sam and if there is no match then the connection request should be treated
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under rules where the source zone is net. It is important that this policy
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be listed BEFORE the next policy (net to all). You can have this policy
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generated for you automatically by using the IMPLICIT_CONTINUE option in
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<ulink url="shorewall.conf.html">shorewall.conf</ulink>(5).</para>
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<para>Partial <filename>/etc/shorewall/rules</filename>:</para>
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<programlisting> #ACTION SOURCE DEST PROTO DEST PORT(S)
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...
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DNAT sam loc:192.168.1.3 tcp ssh
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DNAT net loc:192.168.1.5 tcp www
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...</programlisting>
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<para>Given these two rules, Sam can connect to the firewall's internet
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interface with ssh and the connection request will be forwarded to
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192.168.1.3. Like all hosts in the net zone, Sam can connect to the
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firewall's internet interface on TCP port 80 and the connection request
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will be forwarded to 192.168.1.5. The order of the rules is not
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significant. Sometimes it is necessary to suppress port forwarding for a
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sub-zone. For example, suppose that all hosts can SSH to the firewall and
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be forwarded to 192.168.1.5 EXCEPT Sam. When Sam connects to the
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firewall's external IP, he should be connected to the firewall itself.
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Because of the way that Netfilter is constructed, this requires two rules
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as follows:</para>
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<programlisting> #ACTION SOURCE DEST PROTO DEST PORT(S)
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...
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ACCEPT+ sam $FW tcp ssh
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DNAT net loc:192.168.1.3 tcp ssh
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...</programlisting>
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<para>The first rule allows Sam SSH access to the firewall. The second
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rule says that any clients from the net zone with the exception of those
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in the “sam” zone should have their connection port forwarded to
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192.168.1.3. If you need to exclude more than one zone, simply use
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multiple ACCEPT+ rules. This technique also may be used when the ACTION is
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REDIRECT.</para>
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<para>Care must be taken when nesting occurs as a result of the use of
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wildcard interfaces (interface names ends in '+').</para>
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<para>Here's an example. <filename>/etc/shorewall/zones</filename>:</para>
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<para><filename>/etc/shorewall/interfaces</filename>:<programlisting> #ZONE INTERFACE BROADCAST OPTIONS
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net ppp0
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loc eth1
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loc ppp+
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dmz eth2</programlisting></para>
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<para>Because the net zone is declared before the loc zone, net is an
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implicit sub-zone of loc and in the absence of a net->... CONTINUE
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policy, traffic from the net zone will not be passed through loc->...
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rules. But DNAT and REDIRECT rules are an exception!</para>
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<itemizedlist>
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<listitem>
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<para>DNAT and REDIRECT rules generate two Netfilter rules: a 'nat'
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table rule that rewrites the destination IP address and/or port
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number, and a 'filter' table rule that ACCEPTs the rewritten
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connection.</para>
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</listitem>
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<listitem>
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<para>Policies only affect the 'filter' table.</para>
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</listitem>
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</itemizedlist>
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<para>As a consequence, the following rules will have unexpected
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behavior:<programlisting> #ACTION SOURCE DEST PROTO DEST
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# PORT(S)
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ACCEPT net dmz tcp 80
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REDIRECT loc 3128 tcp 80</programlisting></para>
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<para>The second rule is intended to redirect local web requests to a
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proxy running on the firewall and listening on TCP port 3128. But the
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'nat' part of that rule will cause all connection requests for TCP port 80
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arriving on interface ppp+ (including ppp0!) to have their destination
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port rewritten to 3128. Hence, the web server running in the DMZ will be
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inaccessible from the web.</para>
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<para>The above problem can be corrected in several ways.</para>
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<para>The preferred way is to use the <option>ifname</option> pppd option
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to change the 'net' interface to something other than ppp0. That way, it
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won't match ppp+.</para>
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<para>If you are running Shorewall version 4.1.4 or later, a second way is
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to simply make the nested zones explicit:<programlisting> #ZONE TYPE OPTION
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fw firewall
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loc ipv4
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net:loc ipv4
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dmz ipv4</programlisting></para>
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<para>If you take this approach, be sure to set IMPLICIT_CONTINUE=No in
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<filename>shorewall.conf</filename>.</para>
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<para>When using other Shorewall versions, another way is to rewrite the
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DNAT rule (assume that the local zone is entirely within
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192.168.2.0/23):<programlisting> #ACTION SOURCE DEST PROTO DEST
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# PORT(S)
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ACCEPT net dmz tcp 80
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REDIRECT loc:192.168.2.0/23 3128 tcp 80</programlisting></para>
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<para>Another way is to restrict the definition of the loc zone:</para>
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<para><filename>/etc/shorewall/interfaces</filename>:<programlisting> #ZONE INTERFACE BROADCAST OPTIONS
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net ppp0
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loc eth1
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- ppp+
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dmz eth2</programlisting></para>
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<para><filename>/etc/shorewall/hosts</filename>:<programlisting> #ZONE HOST(S) OPTIONS
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loc ppp+:192.168.2.0/23</programlisting></para>
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</refsect1>
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<refsect1>
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<title>FILES</title>
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<para>/etc/shorewall/zones</para>
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<para>/etc/shorewall/interfaces</para>
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<para>/etc/shorewall/hosts</para>
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<para>/etc/shorewall/policy</para>
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<para>/etc/shorewall/rules</para>
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</refsect1>
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<refsect1>
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<title>See ALSO</title>
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<para>shorewall(8), shorewall-accounting(5), shorewall-actions(5),
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shorewall-blacklist(5), shorewall-hosts(5), shorewall-interfaces(5),
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shorewall-ipsec(5), shorewall-maclist(5), shorewall-masq(5),
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shorewall-nat(5), shorewall-netmap(5), shorewall-params(5),
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shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5),
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shorewall-route_rules(5), shorewall-routestopped(5), shorewall-rules(5),
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shorewall.conf(5), shorewall-tcclasses(5), shorewall-tcdevices(5),
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shorewall-tcrules(5), shorewall-tos(5), shorewall-tunnels(5),
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shorewall-zones(5)</para>
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</refsect1>
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</refentry>
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