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194 lines
8.0 KiB
HTML
194 lines
8.0 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" 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" style="border-collapse: collapse" bordercolor="#111111" width="100%" id="AutoNumber1" bgcolor="#400169" height="90">
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<tr>
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<td width="100%">
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<h1 align="center"><font color="#FFFFFF">Shorewall Troubleshooting</font></h1>
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</td>
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</tr>
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</table>
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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>
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to be sure that there isn't an update that you are missing for your version
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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 common problems.</p>
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<h3 align="Left">If the firewall fails to start</h3>
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If you
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receive an error message when starting or restarting the firewall and you
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can't determine the cause, then do the following:
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<ul>
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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 what
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the problem is.</li>
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<li>If you still can't determine what's wrong then see the
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<a href="support.htm">support page</a>.</li>
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</ul>
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<h3>Your test 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 test setup. Here are several popular snafus: </p>
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<ul>
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<li>Port
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Forwarding where client and server are in the same subnet. See <a href="FAQ.htm">FAQ
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2.</a></li>
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<li>Changing the IP address of a local system to be in the external subnet,
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thinking that Shorewall will suddenly believe that the system is in the
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'net' zone.</li>
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<li>Multiple interfaces connected to the same HUB or Switch. Given the way
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that the Linux kernel respond to ARP "who-has" requests, this type of setup
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does NOT work the way that you expect it to.</li>
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</ul>
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<h3 align="Left">If you are having
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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 TRYING
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TO MAKE IT WORK. Such additional rules will NEVER make it work, they add
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clutter to your rule set and they represent a big security hole in the event
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that you forget to remove them later.</p>
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<p align="Left">I also recommend against setting all of your policies to
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ACCEPT in an effort to make something work. That robs you of one of your
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best diagnostic tools - the "Shorewall" messages that Netfilter will
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generate when you try to connect in a way that isn't permitted by your
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rule set.</p>
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<p align="Left">Check your log. If you don't see Shorewall messages,
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then your problem is probably NOT a Shorewall problem. If you DO see packet
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messages, it is an indication that you are missing one or more rules.</p>
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<p align="Left">While you are troubleshooting, it is a good idea to clear
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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
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OUT=eth1 SRC=192.168.2.2 DST=192.168.1.3 LEN=67 TOS=0x00 PREC=0x00 TTL=63
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ID=5805 DF PROTO=UDP 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 - the packet was rejected under the "all"->"all" REJECT
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policy</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<EFBFBD><EFBFBD><EFBFBD> dmz<6D><7A><EFBFBD> loc<6F><63><EFBFBD> udp<64><70><EFBFBD> 53</p>
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<h3 align="Left">Other Gotchas</h3>
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<ul>
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<li>Remember that Shorewall doesn't automatically allow ICMP type 8 ("ping")
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requests to be sent between zones. If you want pings to be allowed between
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zones, you need a rule of the form:<br>
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<br>
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<20><><EFBFBD> ACCEPT<50><54><EFBFBD> <source zone><EFBFBD><EFBFBD><EFBFBD> <destination zone><EFBFBD><EFBFBD><EFBFBD>
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icmp<EFBFBD><EFBFBD><EFBFBD> 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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<20><><EFBFBD> 10.1.1.2<EFBFBD><EFBFBD><EFBFBD> eth0<68><30><EFBFBD> 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 between
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the zone containing the system you are pinging from and the zone containing
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10.1.1.2, the ping requests will be dropped. This is true even if you
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have NOT specified 'noping' for eth0 in /etc/shorewall/interfaces.</li>
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<li>If you specify "routefilter" for an interface, that interface must be
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up prior to starting the firewall.</li>
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<li>Is your routing correct? For example, internal systems usually need to
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be configured with their default gateway set to the IP address of their
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nearest firewall interface. One often overlooked aspect of routing is that
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in order for two hosts to communicate, the routing between them must be set
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up <u>in both directions.</u> So when setting up routing between <b>A</b>
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and<b> B</b>, be sure to verify that the route from <b>B</b> back to <b>A</b>
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is defined.</li>
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<li>Some versions of LRP (EigerStein2Beta for example) have a shell with
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broken variable expansion. <a href="ftp://ftp.shorewall.net/pub/shorewall/ash.gz">
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You can get a corrected shell from the Shorewall Errata download site.</a>
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</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>Some features require the "ip" program. That program is generally included
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in the "iproute" package which should be included with your distribution
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(though many distributions don't install iproute by default). You
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may also download the latest source tarball from <a href="ftp://ftp.inr.ac.ru/ip-routing" target="_blank">
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ftp://ftp.inr.ac.ru/ip-routing</a>
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.</li>
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<li>If you have <u>any</u> entry for a zone in /etc/shorewall/hosts then the
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zone must be entirely defined in /etc/shorewall/hosts unless you have
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specified MERGE_HOSTS=Yes (Shorewall version 1.3.5 and later). For example, if
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a zone has two interfaces but only one interface has an entry in /etc/shorewall/hosts
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then hosts attached to the other interface will <u>not</u> be considered
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part of the zone.</li>
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<li>Problems with NAT? Be sure that you let Shorewall add all external addresses
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to be use with NAT unless you have set <a href="Documentation.htm#Aliases">
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ADD_IP_ALIASES</a>
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=No 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.</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 7/27/2002 -
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Tom Eastep</font>
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</p>
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<p><font face="Trebuchet MS"><a href="copyright.htm"><font size="2">Copyright</font>
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<20> <font size="2">2001, 2002 Thomas M. Eastep.</font></a></font></p>
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</body>
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</html> |