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209 lines
9.9 KiB
HTML
209 lines
9.9 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type"
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content="text/html; charset=windows-1252">
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<title>Shorewall Troubleshooting</title>
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<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
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<meta name="ProgId" content="FrontPage.Editor.Document">
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</head>
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<body>
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<table border="0" cellpadding="0" cellspacing="0"
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style="border-collapse: collapse;" bordercolor="#111111" width="100%"
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id="AutoNumber1" bgcolor="#3366ff" height="90">
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<tbody>
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<tr>
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<td width="100%">
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<h1 align="center"><font color="#ffffff">Shorewall Troubleshooting<img
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src="images/obrasinf.gif" alt="Beating head on table" width="90"
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height="90" align="middle"> </font></h1>
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</td>
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</tr>
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</tbody>
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</table>
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<h3 style="text-align: center;"><span style="font-style: italic;">"If
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you think you can you can; if you think you can't you're right.<br>
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If you don't believe that you can, why should someone else?" -- Gunnar
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Tapper<br>
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</span></h3>
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<h3 align="left">Check the Errata</h3>
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<p align="left">Check the <a href="errata.htm">Shorewall Errata</a> to
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be sure that there isn't an update that you are missing for your
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version of the firewall.</p>
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<h3 align="left">Check the FAQs</h3>
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<p align="left">Check the <a href="FAQ.htm">FAQs</a> for solutions to
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common problems.</p>
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<h3 align="left">If the firewall fails to start</h3>
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If you receive an error message when starting or restarting the
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firewall and you can't determine the cause, then do the following:
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<ul>
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<li>Make a note of the error message that you see.<br>
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</li>
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<li>shorewall debug start 2> /tmp/trace</li>
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<li>Look at the /tmp/trace file and see if that helps you determine
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what the problem is. Be sure you find the place in the log where the
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error message you saw is generated -- If you are using Shorewall 1.4.0
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or later, you should find the message near the end of the log.</li>
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<li>If you still can't determine what's wrong then see the <a
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href="support.htm">support page</a>.</li>
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</ul>
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Here's an example. During startup, a user sees the following:<br>
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<blockquote>
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<pre>Adding Common Rules<br>iptables: No chain/target/match by that name<br>Terminated<br></pre>
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</blockquote>
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A search through the trace for "No chain/target/match by that name"
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turned up the following:
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<blockquote>
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<pre>+ echo 'Adding Common Rules'<br>+ add_common_rules<br>+ run_iptables -A reject -p tcp -j REJECT --reject-with tcp-reset<br>++ echo -A reject -p tcp -j REJECT --reject-with tcp-reset<br>++ sed 's/!/! /g'<br>+ iptables -A reject -p tcp -j REJECT --reject-with tcp-reset<br>iptables: No chain/target/match by that name<br></pre>
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</blockquote>
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The command that failed was: "iptables -A reject -p tcp -j REJECT
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--reject-with tcp-reset". In this case, the user had compiled his own
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kernel and had
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forgotten to include REJECT target support (see <a href="kernel.htm">kernel.htm</a>)
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<h3>Your network environment</h3>
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<p>Many times when people have problems with Shorewall, the problem is
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actually an ill-conceived network setup. Here are several popular
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snafus: </p>
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<ul>
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<li>Port Forwarding where client and server are in the same subnet.
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See <a href="FAQ.htm">FAQ 2.</a></li>
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<li>Changing the IP address of a local system to be in the external
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subnet, thinking that Shorewall will suddenly believe
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that the system is in the 'net' zone.</li>
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<li>Multiple interfaces connected to the same HUB or Switch. Given
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the way that the Linux kernel respond to ARP "who-has" requests, this
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type of setup does NOT work the way that you expect it to. If you
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are running Shorewall version 1.4.7 or later, you can test using this
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kind of configuration if you specify
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the <span style="font-weight: bold;">arp_filter</span>
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option in /etc/shorewall/interfaces for all interfaces connected to the
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common hub/switch. Using such a setup with a production firewall is
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strongly recommended against.</li>
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</ul>
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<h3 align="left">If you are having connection problems:</h3>
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<p align="left">If the appropriate policy for the connection that you
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are trying to make is ACCEPT, please DO NOT ADD ADDITIONAL ACCEPT RULES
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TRYING TO MAKE IT WORK. Such additional rules will NEVER make it work,
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they add clutter to your rule set and they represent a big security
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hole
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in the event that you forget to remove them later.</p>
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<p align="left">I also recommend against setting all of your policies
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to ACCEPT in an effort to make something work. That robs you of one of
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your best diagnostic tools - the "Shorewall" messages that Netfilter
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will generate when you try to connect in a way that isn't permitted by
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your rule set.</p>
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<p align="left">Check your log ("/sbin/shorewall show log"). If you
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don't see Shorewall messages, then your problem is probably NOT a
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Shorewall problem. If you DO see packet messages, it may be an
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indication that
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you are missing one or more rules -- see <a href="FAQ.htm#faq17">FAQ 17</a>.</p>
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<p align="left">While you are troubleshooting, it is a good idea to
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clear two variables in /etc/shorewall/shorewall.conf:</p>
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<p align="left">LOGRATE=""<br>
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LOGBURST=""</p>
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<p align="left">This way, you will see all of the log messages being
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generated (be sure to restart shorewall after clearing these variables).</p>
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<p align="left">Example:</p>
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<font face="Century Gothic, Arial, Helvetica">
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<p align="left"><font face="Courier">Jun 27 15:37:56 gateway kernel:
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Shorewall:all2all:REJECT:IN=eth2 OUT=eth1 SRC=192.168.2.2
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DST=192.168.1.3 LEN=67 TOS=0x00 PREC=0x00 TTL=63 ID=5805 DF PROTO=UDP
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SPT=1803 DPT=53 LEN=47</font></p>
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</font>
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<p align="left">Let's look at the important parts of this message:</p>
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<ul>
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<li>all2all:REJECT - This packet was REJECTed out of the
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all2all chain -- the packet was rejected under the "all"->"all"
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REJECT policy (see <a href="FAQ.htm#faq17">FAQ 17).</a></li>
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<li>IN=eth2 - the packet entered the firewall via eth2</li>
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<li>OUT=eth1 - if accepted, the packet would be sent on eth1</li>
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<li>SRC=192.168.2.2 - the packet was sent by 192.168.2.2</li>
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<li>DST=192.168.1.3 - the packet is destined for 192.168.1.3</li>
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<li>PROTO=UDP - UDP Protocol</li>
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<li>DPT=53 - DNS</li>
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</ul>
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<p align="left">In this case, 192.168.2.2 was in the "dmz" zone and
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192.168.1.3 is in the "loc" zone. I was missing the rule:</p>
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<p align="left">ACCEPT dmz
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loc udp 53<br>
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</p>
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<p align="left">See <a href="FAQ.htm#faq17">FAQ 17</a> for additional
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information about how to interpret the chain name appearing in a
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Shorewall log message.<br>
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</p>
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<h3 align="left">'Ping' Problems?</h3>
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Either can't ping when you think you should be able to or are able to
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ping when you think that you shouldn't be allowed? Shorewall's 'Ping'
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Management<a href="ping.html"> is described here</a>.<br>
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<h3 align="left">Other Gotchas</h3>
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<ul>
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<li>Seeing rejected/dropped packets logged out of the INPUT or
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FORWARD chains? This means that:
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<ol>
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<li>your zone definitions are screwed up and the host that is
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sending the packets or the destination host isn't in any zone (using an
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<a href="Documentation.htm#Hosts">/etc/shorewall/hosts</a> file
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are you?); or</li>
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<li>the source and destination hosts are both connected to the
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same interface and you don't have a policy or rule for the
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source zone to or from the destination zone.</li>
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</ol>
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</li>
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<li>Remember that Shorewall doesn't automatically allow ICMP type 8
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("ping") requests to be sent between zones. If you want pings to be
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allowed between zones, you need a rule of the form:<br>
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<br>
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ACCEPT <source
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zone> <destination zone>
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icmp echo-request<br>
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<br>
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The ramifications of this can be subtle. For example, if you have the
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following in /etc/shorewall/nat:<br>
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<br>
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10.1.1.2 eth0
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130.252.100.18<br>
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<br>
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and you ping 130.252.100.18, unless you have allowed icmp type 8
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between the zone containing the system you are pinging from and the
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zone containing 10.1.1.2, the ping requests will be dropped. </li>
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<li>If you specify "routefilter" for an interface, that interface
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must be up prior to starting the firewall.</li>
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<li>Is your routing correct? For example, internal systems usually
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need to be configured with their default gateway set to
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the IP address of their nearest firewall interface. One often
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overlooked aspect of routing is that in order for two hosts to
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communicate,
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the routing between them must be set up <u>in both directions.</u>
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So when setting up routing between <b>A</b> and<b> B</b>, be sure
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to verify that the route from <b>B</b> back to <b>A</b> is defined.</li>
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<li>Some versions of LRP (EigerStein2Beta for example) have a shell
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with broken variable expansion. <a
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href="ftp://ftp.shorewall.net/pub/shorewall/ash.gz"> You can get a
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corrected shell from the Shorewall Errata download site.</a> </li>
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<li>Do you have your kernel properly configured? <a href="kernel.htm">Click
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here to see my kernel configuration.</a> </li>
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<li>Shorewall requires the "ip" program. That program is generally
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included in the "iproute" package which should be included with your
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distribution (though many distributions don't install iproute by
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default). You may also download the latest source tarball from <a
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href="ftp://ftp.inr.ac.ru/ip-routing" target="_blank">
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ftp://ftp.inr.ac.ru/ip-routing</a> .</li>
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<li>Problems with NAT? Be sure that you let
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Shorewall add all external addresses to be use with NAT unless you
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have set <a href="Documentation.htm#Aliases"> ADD_IP_ALIASES</a> =No
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in /etc/shorewall/shorewall.conf.</li>
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</ul>
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<h3>Still Having Problems?</h3>
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<p>See the<a href="support.htm"> support page.<br>
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</a></p>
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<font face="Century Gothic, Arial, Helvetica">
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<blockquote> </blockquote>
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</font>
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<p><font size="2">Last updated 8/29/2003 - Tom Eastep</font> </p>
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<p><font face="Trebuchet MS"><a href="copyright.htm"><font size="2">Copyright</font>
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<EFBFBD> <font size="2">2001, 2002 Thomas M. Eastep.</font></a></font><br>
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</p>
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<br>
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</body>
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</html>
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