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Setting up a Linux system as a firewall for a small network is a fairly straight-forward task if you understand the basics and follow the documentation.
This guide doesn't attempt to acquaint you with all of the features of Shorewall. It rather focuses on what is required to configure Shorewall in its most common configuration:
<para><emphasisrole="bold">Single public IP address.</emphasis> If you have more than one public IP address, this is not the guide you want -- see the <ulinkurl="shorewall_setup_guide.htm">Shorewall Setup Guide</ulink> instead.
<figurelabel="1"><title>Common two interface firewall configuration</title><mediaobject><imageobject><imagedatafileref="images/basics.png"format="PNG"/></imageobject></mediaobject></figure>
<tip><title>Shorewall and <trademark>Mandrake</trademark> 9.0+</title><para>
If you are running Shorewall under <trademark>Mandrake</trademark> 9.0 or later, you can easily configure the above setup using the <trademark>Mandrake</trademark><quote>Internet Connection Sharing</quote> applet. From the <emphasis><interface>Mandrake Control Center</interface></emphasis>, select <quote><guimenuitem>Network</guimenuitem>&<guisubmenu>Internet</guisubmenu></quote> then <quote><interface>Connection Sharing</interface></quote>.
Note however, that the Shorewall configuration produced by <emphasis>Mandrake Internet Connection Sharing</emphasis> is strange and is apt to confuse you if you use the rest of this documentation (it has two local zones; <varname>loc</varname> and <varname>masq</varname> where <varname>loc</varname> is empty; this conflicts with this documentation which assumes a single local zone <varname>loc</varname>). We therefore recommend that once you have set up this sharing that you uninstall the <trademark>Mandrake</trademark> Shorewall RPM and install the one from the <ulinkurl="download.htm">download</ulink> page then follow the instructions in this Guide.
If you edit your configuration files on a <trademark>Windows</trademark> system, you must save them as <trademark>Unix</trademark> files if your editor supports that option or you must run them through <command>dos2unix</command> before trying to use them. Similarly, if you copy a configuration file from your <trademark>Windows</trademark> hard drive to a floppy disk, you must run <command>dos2unix</command> against the copy before using it with Shorewall.
<itemizedlist><listitem><para><ulinkurl="http://www.simtel.net/pub/pd/51438.html"><trademark>Windows</trademark> Version of <command>dos2unix</command></ulink></para></listitem><listitem><para><ulinkurl="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux Version of <command>dos2unix</command></ulink></para></listitem></itemizedlist>
Shorewall requires that you have the <command>iproute</command>/<command>iproute2</command> package installed (on <trademark>RedHat</trademark>, the package is called <command>iproute</command>). You can tell if this package is installed by the presence of an <command>ip</command> program on your firewall system. As <systemitemclass="username">root</systemitem>, you can use the <command>which</command> command to check for this program:
<programlisting>
[root@gateway root]# which ip
/sbin/ip
[root@gateway root]#
</programlisting>
I recommend that you first read through the guide to familiarize yourself with what's involved then go back through it again making your configuration changes.
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>If you have an <acronym>ADSL</acronym> Modem and you use <acronym>PPTP</acronym> to communicate with a server in that modem, you must make the changes recommended here in addition to those detailed below. <acronym>ADSL</acronym> with <acronym>PPTP</acronym> is most commonly found in Europe, notably in Austria.
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>The configuration files for Shorewall are contained in the directory <filenameclass="directory">/etc/shorewall</filename> -- for simple setups, you will only need to deal with a few of these as described in this guide.
After you have <ulinkurl="Install.htm">installed Shorewall</ulink>, download the <ulinkurl="http://www1.shorewall.net/pub/shorewall/Samples/">two-interface sample</ulink>, un-tar it (<command>tar <option>-zxvf</option><filename>two-interfaces.tgz</filename></command>) and and copy the files to <filenameclass="directory">/etc/shorewall</filename><emphasisrole="bold">(these files will replace files with the same name)</emphasis>.
As each file is introduced, I suggest that you look through the actual file on your system -- each file contains detailed configuration instructions and default entries.
Shorewall views the network where it is running as being composed of a set of zones. In the two-interface sample configuration, the following zone names are used:
<informaltableframe="all"pgwide="0"><tgroupcols="2"align="left"><theadvalign="middle"><rowvalign="middle"><entryalign="left">Name</entry><entryalign="left">Description</entry></row></thead><tbodyvalign="middle"><rowvalign="middle"><entryalign="left"><varname>net</varname></entry><entryalign="left">The Internet</entry></row><rowvalign="middle"><entryalign="left"><varname>loc</varname></entry><entryalign="left">Your Local Network</entry></row><rowvalign="middle"><entryalign="left"><varname>dmz</varname></entry><entryalign="left">Demilitarized Zone</entry></row></tbody></tgroup></informaltable>
Zones are defined in the <ulinkurl="Documentation.htm#Zones"><filenameclass="directory">/etc/shorewall/</filename><filename>zones</filename></ulink> file.
You express your default policy for connections from one zone to another zone in the <ulinkurl="Documentation.htm#Policy"><filenameclass="directory">/etc/shorewall/</filename><filename>policy</filename></ulink> file.
You define exceptions to those default policies in the <ulinkurl="Documentation.htm#Rules"><filenameclass="directory">/etc/shorewall/</filename><filename>rules</filename></ulink> file.
For each connection request entering the firewall, the request is first checked against the <filenameclass="directory">/etc/shorewall/</filename><filename>rules</filename> file. If no rule in that file matches the connection request then the first policy in <filenameclass="directory">/etc/shorewall/</filename><filename>policy</filename> that matches the request is applied. If that policy is <varname>REJECT</varname> or <varname>DROP</varname> the request is first checked against the rules in <filenameclass="directory">/etc/shorewall/</filename><filename>common</filename> if that file exists; otherwise the rules in <filenameclass="directory">/etc/shorewall/</filename><filename>common.def</filename> are checked.
The <filenameclass="directory">/etc/shorewall/</filename><filename>policy</filename> file included with the two-interface sample has the following policies:
In the two-interface sample, the line below is included but commented out. If you want your firewall system to have full access to servers on the internet, uncomment that line.
Allow all connection requests from your local network to the internet
</para></listitem><listitem><para>
Drop (ignore) all connection requests from the internet to your firewall or local network
</para></listitem><listitem><para>
Optionally accept all connection requests from the firewall to the internet (if you uncomment the additional policy)
</para></listitem><listitem><para>
reject all other connection requests.
</para></listitem></itemizedlist>
<inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>At this point, edit your <filenameclass="directory">/etc/shorewall/</filename><filename>policy</filename> and make any changes that you wish.
The firewall has two network interfaces. Where Internet connectivity is through a cable or <acronym>DSL</acronym><quote>Modem</quote>, the <emphasis>External Interface</emphasis> will be the ethernet adapter that is connected to that <quote>Modem</quote> (e.g., <filenameclass="devicefile">eth0</filename>) unless you connect via <emphasis>Point-to-Point Protocol</emphasis> over Ethernet (<acronym>PPPoE</acronym>) or <emphasis>Point-to-Point Tunneling Protocol</emphasis> (<acronym>PPTP</acronym>) in which case the External Interface will be a <literal>ppp</literal> interface (e.g., <filenameclass="devicefile">ppp0</filename>). If you connect via a regular modem, your External Interface will also be <filenameclass="devicefile">ppp0</filename>. If you connect via <acronym>ISDN</acronym>, your external interface will be <filenameclass="devicefile">ippp0</filename>.
</para>
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>If your external interface is <filenameclass="devicefile">ppp0</filename> or <filenameclass="devicefile">ippp0</filename> then you will want to set <varname>CLAMPMSS=yes</varname> in <filenameclass="directory">/etc/shorewall/</filename><filename>shorewall.conf</filename>.
</para>
<para>
Your <emphasis>Internal Interface</emphasis> will be an ethernet adapter (<filenameclass="devicefile">eth1</filename> or <filenameclass="devicefile">eth0</filename>) and will be connected to a hub or switch. Your other computers will be connected to the same hub/switch (note: If you have only a single internal system, you can connect the firewall directly to the computer using a cross-over cable).
<warning><para>
Do not connect the internal and external interface to the same hub or switch except for testing AND you are running Shorewall version 1.4.7 or later. When using these recent versions, you can test using this kind of configuration if you specify the arp_filter option in <filenameclass="directory">/etc/shorewall/</filename><filename>interfaces</filename> for all interfaces connected to the common hub/switch. Using such a setup with a production firewall is strongly recommended against.
</para></warning>
<inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>The Shorewall two-interface sample configuration assumes that the external interface is <filenameclass="devicefile">eth0</filename> and the internal interface is <filenameclass="devicefile">eth1</filename>. If your configuration is different, you will have to modify the sample <filenameclass="directory">/etc/shorewall/</filename><filename>interfaces</filename> file accordingly. While you are there, you may wish to review the list of options that are specified for the interfaces. Some hints:
<itemizedlistspacing="compact"><listitem><para>
If your external interface is <filenameclass="devicefile">ppp0</filename> or <filenameclass="devicefile">ippp0</filename>, you can replace the <varname>detect</varname> in the second column with a <quote>-</quote> (minus the quotes).
</para></listitem><listitem><para>
If your external interface is <filenameclass="devicefile">ppp0</filename> or <filenameclass="devicefile">ippp0</filename> or if you have a static <acronym>IP</acronym> address, you can remove <varname>dhcp</varname> from the option list.
</para></listitem></itemizedlist>
</para>
</section>
<section>
<title>IP Addresses</title>
<para>
Before going further, we should say a few words about Internet Protocol (<acronym>IP</acronym>) addresses. Normally, your <acronym>ISP</acronym> will assign you a single Public IP address. This address may be assigned via the Dynamic Host Configuration Protocol (<acronym>DHCP</acronym>) or as part of establishing your connection when you dial in (standard modem) or establish your <acronym>PPP</acronym> connection. In rare cases, your <acronym>ISP</acronym> may assign you a static <acronym>IP</acronym> address; that means that you configure your firewall's external interface to use that address permanently. However your external address is assigned, it will be shared by all of your systems when you access the Internet. You will have to assign your own addresses in your internal network (the Internal Interface on your firewall plus your other computers). <emphasisrole="bold">RFC 1918</emphasis> reserves several <emphasis>Private</emphasis><acronym>IP</acronym> address ranges for this purpose:
<programlisting>
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
</programlisting>
<inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>Before starting Shorewall, you should look at the IP address of your external interface and if it is one of the above ranges, you should remove the 'norfc1918' option from the external interface's entry in <filenameclass="directory">/etc/shorewall/</filename><filename>interfaces</filename>.
</para>
<para>
You will want to assign your addresses from the same sub-network (subnet). For our purposes, we can consider a subnet to consists of a range of addresses <varname>x.y.z.0 - x.y.z.255</varname>. Such a subnet will have a Subnet Mask of <systemitemclass="netmask">255.255.255.0</systemitem>. The address <varname>x.y.z.0</varname> is reserved as the <emphasis>Subnet Address</emphasis> and <varname>x.y.z.255</varname> is reserved as the <emphasis>Subnet Broadcast Address</emphasis>. In Shorewall, a subnet is described using <ulinkurl="shorewall_setup_guide.htm#Subnets">Classless InterDomain Routing (CIDR) notation</ulink> with consists of the subnet address followed by <varname>/24</varname>. The <quote>24</quote> refers to the number of consecutive leading <quote>1</quote> bits from the left of the subnet mask.
It is conventional to assign the internal interface either the first usable address in the subnet (<systemitemclass="ipaddress">10.10.10.1</systemitem> in the above example) or the last usable address (<systemitemclass="ipaddress">10.10.10.254</systemitem>).
</para>
<para>
One of the purposes of subnetting is to allow all computers in the subnet to understand which other computers can be communicated with directly. To communicate with systems outside of the subnetwork, systems send packets through a gateway (router).
</para>
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>Your local computers (computer 1 and computer 2 in the above diagram) should be configured with their default gateway to be the <acronym>IP</acronym> address of the firewall's internal interface.
</para>
<para>
The foregoing short discussion barely scratches the surface regarding subnetting and routing. If you are interested in learning more about <acronym>IP</acronym> addressing and routing, I highly recommend <quote>IP Fundamentals: What Everyone Needs to Know about Addressing & Routing</quote>, Thomas A. Maufer, Prentice-Hall, 1999, ISBN 0-13-975483-0 (<ulinkurl="http://www.phptr.com/browse/product.asp?product_id={58D4F6D4-54C5-48BA-8EDD-86EBD7A42AF6}">link</ulink>).
</para>
<para>
The remainder of this quide will assume that you have configured your network as shown here:
The default gateway for computer's 1 & 2 would be <systemitemclass="ipaddress">10.10.10.254</systemitem>.
<warning><para>
Your <acronym>ISP</acronym> might assign your external interface an <emphasisrole="bold">RFC 1918</emphasis> address. If that address is in the <systemitemclass="ipaddress">10.10.10.0/24</systemitem> subnet then you will need to select a DIFFERENT RFC 1918 subnet for your local network.
</para></warning>
</para>
</section>
<section>
<title>IP Masquerading (SNAT)</title>
<para>
The addresses reserved by RFC 1918 are sometimes referred to as non-routable because the Internet backbone routers don't forward packets which have an RFC-1918 destination address. When one of your local systems (let's assume computer 1) sends a connection request to an internet host, the firewall must perform <emphasis>Network Address Translation</emphasis> (<acronym>NAT</acronym>). The firewall rewrites the source address in the packet to be the address of the firewall's external interface; in other words, the firewall makes it look as if the firewall itself is initiating the connection. This is necessary so that the destination host will be able to route return packets back to the firewall (remember that packets whose destination address is reserved by RFC 1918 can't be routed across the internet so the remote host can't address its response to computer 1). When the firewall receives a return packet, it rewrites the destination address back to <systemitemclass="ipaddress">10.10.10.1</systemitem> and forwards the packet on to computer 1.
</para>
<para>
On Linux systems, the above process is often referred to as <emphasis>IP Masquerading</emphasis> but you will also see the term <emphasis>Source Network Address Translation</emphasis> (<acronym>SNAT</acronym>) used. Shorewall follows the convention used with Netfilter:
<itemizedlist><listitem><para><emphasis>Masquerade</emphasis> describes the case where you let your firewall system automatically detect the external interface address.
</para></listitem><listitem><para><emphasis><acronym>SNAT</acronym></emphasis> refers to the case when you explicitly specify the source address that you want outbound packets from your local network to use.
</para></listitem></itemizedlist>
In Shorewall, both <emphasis>Masquerading</emphasis> and <emphasis><acronym>SNAT</acronym></emphasis> are configured with entries in the <filenameclass="directory">/etc/shorewall/</filename><filename>masq</filename> file. You will normally use Masquerading if your external <acronym>IP</acronym> is dynamic and <acronym>SNAT</acronym> if the <acronym>IP</acronym> is static.
</para>
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>If your external firewall interface is <filenameclass="devicefile">eth0</filename>, you do not need to modify the file provided with the sample. Otherwise, edit <filenameclass="directory">/etc/shorewall/</filename><filename>masq</filename> and change the first column to the name of your external interface and the second column to the name of your internal interface.
</para>
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>If your external <acronym>IP</acronym> is static, you can enter it in the third column in the <filenameclass="directory">/etc/shorewall/</filename><filename>masq</filename> entry if you like although your firewall will work fine if you leave that column empty. Entering your static <acronym>IP</acronym> in column 3 makes processing outgoing packets a little more efficient.
</para>
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>If you are using the Debian package, please check your <filename>shorewall.conf</filename> file to ensure that the following are set correctly; if they are not, change them appropriately:
<itemizedlistspacing="compact"><listitem><para><varname>NAT_ENABLED=Yes</varname> (Shorewall versions earlier than 1.4.6)
One of your goals may be to run one or more servers on your local computers. Because these computers have RFC-1918 addresses, it is not possible for clients on the internet to connect directly to them. It is rather necessary for those clients to address their connection requests to the firewall who rewrites the destination address to the address of your server and forwards the packet to that server. When your server responds, the firewall automatically performs <acronym>SNAT</acronym> to rewrite the source address in the response.
</para>
<para>
The above process is called <emphasis>Port Forwarding</emphasis> or <emphasis>Destination Network Address Translation</emphasis> (<acronym>DNAT</acronym>). You configure port forwarding using <acronym>DNAT</acronym> rules in the <filenameclass="directory">/etc/shorewall/</filename><filename>rules</filename> file.
</para>
<para>
The general form of a simple port forwarding rule in <filenameclass="directory">/etc/shorewall/</filename><filename>rules</filename> is:
<informaltableframe="all"pgwide="0"label="rules"><tgroupcols="7"align="left"><theadvalign="middle"><rowvalign="middle"><entryalign="left">ACTION</entry><entryalign="left">SOURCE</entry><entryalign="left">DESTINATION</entry><entryalign="left">PROTOCOL</entry><entryalign="left">PORT</entry><entryalign="left">SOURCE PORT</entry><entryalign="left">ORIGINAL ADDRESS</entry></row></thead><tbody><row><entryalign="left"><varname>DNAT</varname></entry><entryalign="left"><varname>net</varname></entry><entryalign="left"><varname>loc:<server local ip address> [:<server port>]</varname></entry><entryalign="left"><varname><protocol></varname></entry><entryalign="left"><varname><port></varname></entry><entry/><entry/></row></tbody></tgroup></informaltable>
<examplelabel="1"><title>Web Server</title><para>
You run a Web Server on computer 2 and you want to forward incoming <acronym>TCP</acronym> port 80 to that system:
For <acronym>FTP</acronym>, you will also need to have <acronym>FTP</acronym> connection tracking and <acronym>NAT</acronym> support in your kernel. For vendor-supplied kernels, this means that the <filenameclass="libraryfile">ip_conntrack_ftp</filename> and <filenameclass="libraryfile">ip_nat_ftp</filename> modules must be loaded. Shorewall will automatically load these modules if they are available and located in the standard place under <filenameclass="directory">/lib/modules/<kernel version>/kernel/net/ipv4/netfilter</filename>.
</para></example>
A couple of important points to keep in mind:
<itemizedlist><listitem><para>
You must test the above rule from a client outside of your local network (i.e., don't test from a browser running on computers 1 or 2 or on the firewall). If you want to be able to access your web server and/or <acronym>FTP</acronym> server from inside your firewall using the <acronym>IP</acronym> address of your external interface, see <ulinkurl="FAQ.htm#faq2">Shorewall FAQ #2</ulink>.
</para></listitem><listitem><para>
Many <acronym>ISP</acronym>s block incoming connection requests to port 80. If you have problems connecting to your web server, try the following rule and try connecting to port 5000.
<inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>At this point, modify <filenameclass="directory">/etc/shorewall/</filename><filename>rules</filename> to add any <acronym>DNAT</acronym> rules that you require.
</para>
</section>
<section>
<title>Domain Name Server (DNS)</title>
<para>
Normally, when you connect to your ISP, as part of getting an IP address your firewall's <emphasis>Domain Name Service</emphasis> (<acronym>DNS</acronym>) resolver will be automatically configured (e.g., the <filenameclass="directory">/etc/</filename><filename>resolv.conf</filename> file will be written). Alternatively, your ISP may have given you the <acronym>IP</acronym> address of a pair of <acronym>DNS</acronym> name servers for you to manually configure as your primary and secondary name servers. Regardless of how <acronym>DNS</acronym> gets configured on your firewall, it is your responsibility to configure the resolver in your internal systems. You can take one of two approaches:
<itemizedlistspacing="compact"><listitem><para>
You can configure your internal systems to use your ISP's name servers. If you ISP gave you the addresses of their servers or if those addresses are available on their web site, you can configure your internal systems to use those addresses. If that information isn't available, look in /etc/resolv.conf on your firewall system -- the name servers are given in "nameserver" records in that file.
You can configure a <emphasis>Caching Name Server</emphasis> on your firewall. <trademark>Red Hat</trademark> has an <acronym>RPM</acronym> for a caching name server (the <acronym>RPM</acronym> also requires the <command>bind</command><acronym>RPM</acronym>) and for Bering users, there is <command>dnscache.lrp</command>. If you take this approach, you configure your internal systems to use the firewall itself as their primary (and only) name server. You use the internal <acronym>IP</acronym> address of the firewall (<systemitemclass="ipaddress">10.10.10.254</systemitem> in the example above) for the name server address. To allow your local systems to talk to your caching name server, you must open port 53 (both <acronym>UDP</acronym> and <acronym>TCP</acronym>) from the local network to the firewall; you do that by adding the following rules in <filenameclass="directory">/etc/shorewall/</filename><filename>rules</filename>.
Those rules allow <acronym>DNS</acronym> access from your firewall and may be removed if you uncommented the line in <filenameclass="directory">/etc/shorewall/</filename><filename>policy</filename> allowing all connections from the firewall to the internet.
<example><title>Web Server on Firewall</title><para>
You want to run a Web Server on your firewall system:
<informaltableframe="all"pgwide="0"label="rules"><tgroupcols="7"align="left"><colspeccolname="c1"/><colspeccolname="c2"/><colspeccolname="c3"/><colspeccolname="c4"/><colspeccolname="c5"/><colspeccolname="c6"/><colspeccolname="c7"/><theadvalign="middle"><rowvalign="middle"><entryalign="left">ACTION</entry><entryalign="left">SOURCE</entry><entryalign="left">DESTINATION</entry><entryalign="left">PROTOCOL</entry><entryalign="left">PORT</entry><entryalign="left">SOURCE PORT</entry><entryalign="left">ORIGINAL ADDRESS</entry></row></thead><tbody><row><entryalign="left"><varname>ACCEPT</varname></entry><entryalign="left"><varname>net</varname></entry><entryalign="left"><varname>fw</varname></entry><entryalign="left"><varname>tcp</varname></entry><entryalign="left"><varname>80</varname></entry><entrynamest="c6"nameend="c7">#Allow web access from the Internet</entry></row><row><entryalign="left"><varname>ACCEPT</varname></entry><entryalign="left"><varname>loc</varname></entry><entryalign="left"><varname>fw</varname></entry><entryalign="left"><varname>tcp</varname></entry><entryalign="left"><varname>80</varname></entry><entrynamest="c6"nameend="c7">#Allow web access from the local network</entry></row></tbody></tgroup></informaltable>
Those two rules would of course be in addition to the rules listed above under <quote><linklinkend="cachingdns">You can configure a Caching Name Server on your firewall</link></quote>.
</para></example>
If you don't know what port and protocol a particular application uses, look <ulinkurl="ports.htm">here</ulink>.
<important><para>
I don't recommend enabling <command>telnet</command> to/from the internet because it uses clear text (even for login!). If you want shell access to your firewall from the internet, use <acronym>SSH</acronym>:
<inlinegraphicfileref="images/leaflogo.gif"format="GIF"/>Bering users will want to add the following two rules to be compatible with Jacques's Shorewall configuration.
<informaltableframe="all"pgwide="0"label="rules"><tgroupcols="7"align="left"><colspeccolname="c1"/><colspeccolname="c2"/><colspeccolname="c3"/><colspeccolname="c4"/><colspeccolname="c5"/><colspeccolname="c6"/><colspeccolname="c7"/><theadvalign="middle"><rowvalign="middle"><entryalign="left">ACTION</entry><entryalign="left">SOURCE</entry><entryalign="left">DESTINATION</entry><entryalign="left">PROTOCOL</entry><entryalign="left">PORT</entry><entryalign="left">SOURCE PORT</entry><entryalign="left">ORIGINAL ADDRESS</entry></row></thead><tbody><row><entryalign="left"><varname>ACCEPT</varname></entry><entryalign="left"><varname>loc</varname></entry><entryalign="left"><varname>fw</varname></entry><entryalign="left"><varname>udp</varname></entry><entryalign="left"><varname>53</varname></entry><entrynamest="c6"nameend="c7">#Allow DNS Cache to work</entry></row><row><entryalign="left"><varname>ACCEPT</varname></entry><entryalign="left"><varname>loc</varname></entry><entryalign="left"><varname>fw</varname></entry><entryalign="left"><varname>tcp</varname></entry><entryalign="left"><varname>80</varname></entry><entrynamest="c6"nameend="c7">#Allow weblet to work</entry></row></tbody></tgroup></informaltable>
<inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>Now edit your <filenameclass="directory">/etc/shorewall/</filename><filename>rules</filename> file to add or delete other connections as required.
</para>
</section>
<section>
<title>Starting and Stopping Your Firewall</title>
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>The <ulinkurl="Install.htm">installation procedure</ulink> configures your system to start Shorewall at system boot but beginning with Shorewall version 1.3.9 startup is disabled so that your system won't try to start Shorewall before configuration is complete. Once you have completed configuration of your firewall, you can enable Shorewall startup by removing the file <filenameclass="directory">/etc/shorewall/</filename><filename>startup_disabled</filename>.
<important><para>
Users of the .deb package must edit <filenameclass="directory">/etc/default/</filename><filename>shorewall</filename> and set <varname>startup=1</varname>.
</para></important>
The firewall is started using the <quote><command>shorewall start</command></quote> command and stopped using <quote><command>shorewall stop</command></quote>. When the firewall is stopped, routing is enabled on those hosts that have an entry in <filenameclass="directory">/etc/shorewall/</filename><filename><ulinkurl="Documentation.htm#Routestopped">routestopped</ulink></filename>. A running firewall may be restarted using the <quote><command>shorewall restart</command></quote> command. If you want to totally remove any trace of Shorewall from your Netfilter configuration, use <quote><command>shorewall clear</command></quote>.
</para>
<para><inlinegraphicfileref="images/BD21298_.gif"format="GIF"/>The two-interface sample assumes that you want to enable routing to/from <filenameclass="devicefile">eth1</filename> (the local network) when Shorewall is stopped. If your local network isn't connected to <filenameclass="devicefile">eth1</filename> or if you wish to enable access to/from other hosts, change <filenameclass="directory">/etc/shorewall/</filename><filename>routestopped</filename> accordingly.
<warning><para>
If you are connected to your firewall from the internet, do not issue a <quote><command>shorewall stop</command></quote> command unless you have added an entry for the <acronym>IP</acronym> address that you are connected from to <filenameclass="directory">/etc/shorewall/</filename><filename>routestopped</filename>. Also, I don't recommend using <quote><command>shorewall restart</command></quote>; it is better to create an alternate configuration and test it using the <quote><command>shorewall try</command></quote> command.
</para></warning></para>
</section>
<section>
<title>Additional Recommended Reading</title>
<para>
I highly recommend that you review the <ulinkurl="configuration_file_basics.htm">Common Configuration File Features page</ulink> -- it contains helpful tips about Shorewall features than make administering your firewall easier.
