forked from extern/shorewall_code
d282399aa7
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@548 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
1299 lines
68 KiB
HTML
1299 lines
68 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-Language" content="en-us">
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<meta http-equiv="Content-Type"
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content="text/html; charset=windows-1252">
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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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<title>Shorewall FAQ</title>
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<meta name="Microsoft Theme" content="none">
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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;" width="100%" id="AutoNumber4"
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bgcolor="#400169" height="90">
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<tbody>
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<tr>
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<td
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width="100%">
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<h1 align="center"><font color="#ffffff">Shorewall FAQs</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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<h1>Looking for Step by Step Configuration Instructions? Check out the <a
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href="shorewall_quickstart_guide.htm">QuickStart Guides</a>. <br>
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</h1>
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<h1>PORT FORWARDING<br>
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</h1>
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<p align="left"><b>1. </b><a href="#faq1"> I want to <b>forward</b> UDP <b>
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port</b> 7777 to my my personal PC with IP address
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192.168.1.5. I've looked everywhere and can't find
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<b>how to do it</b>.</a></p>
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<p align="left"><b>1a. </b><a href="#faq1a">Ok -- I followed those instructions
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but it doesn't work.<br>
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</a></p>
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<p align="left"><b>1b. </b><a href="#faq1b">I'm still having problems with
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port forwarding</a></p>
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<p align="left"><b>1c. </b><a href="#faq1c">From the internet, I want to
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<b>connect to port 1022</b> on my firewall and have the <b>firewall forward
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the connection to port 22 on local system 192.168.1.3</b>. How do I do that?</a><br>
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</p>
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<h1><b>DNS and PORT FORWARDING/NAT<br>
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</b></h1>
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<p align="left"><b>2.</b> <a href="#faq2">I <b>port forward</b> www requests
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to www.mydomain.com (IP 130.151.100.69) to system
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192.168.1.5 in my local network. <b>External clients
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can browse</b> http://www.mydomain.com but <b>internal
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clients can't</b>.</a></p>
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<p align="left"><b>2a. </b><a href="#faq3">I have a zone "Z" with an RFC1918
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subnet and I use <b>static NAT</b> to assign non-RFC1918
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addresses to hosts in Z. Hosts in Z cannot communicate
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with each other using their external (non-RFC1918 addresses)
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so they <b>can't access each other using their DNS names.</b></a></p>
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<h1><b>NETMEETING/MSN<br>
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</b></h1>
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<p align="left"><b>3. </b><a href="#faq3">I want to use <b>Netmeeting</b>
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or <b>MSN Instant Messenger </b>with Shorewall.
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What do I do?</a></p>
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<h1><b>OPEN PORTS<br>
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</b></h1>
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<p align="left"><b>4. </b><a href="#faq4">I just used an online port scanner
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to check my firewall and it shows <b>some ports
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as 'closed' rather than 'blocked'.</b> Why?</a></p>
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<p align="left"><b>4a. </b><a href="#faq4a">I just ran an <b>nmap UDP scan</b>
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of my firewall and it showed 100s of ports as
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open!!!!<br>
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</a></p>
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<b>4b</b>. <a href="#faq4b">I have a port that I can't close no matter how
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I change my rules.<2E></a>
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<h1>CONNECTION PROBLEMS</h1>
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<p align="left"><b>5. </b><a href="#faq5">I've installed Shorewall and now
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I <b> can't ping</b> through the firewall</a><br>
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<b><br>
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15. </b><a href="#faq15"><b>My local systems can't see out
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to the net</b></a></p>
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<h1>LOGGING<br>
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</h1>
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<p align="left"><b>6. </b><a href="#faq6">Where are the <b>log messages</b>
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written and how do I <b>change the destination</b>?</a></p>
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<p align="left"><b>6a. </b><a href="#faq6a">Are there any <b>log parsers</b>
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that work with Shorewall?</a></p>
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<p align="left"><b>6b. <a href="#faq6b">DROP messages</a></b><a
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href="#faq6b"> on port 10619 are <b>flooding the logs</b> with their connect
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requests. Can i exclude these error messages for this port temporarily
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from logging in Shorewall?</a><br>
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</p>
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<p align="left"><b>6c. </b><a href="#faq6c">All day long I get a steady flow
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of these <b>DROP messages from port 53</b> <b>to some high numbered
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port</b>. They get dropped, but what the heck are they?</a><br>
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</p>
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<p align="left"><b>6d.</b> <a href="#faq6d">Why is the <b>MAC address</b>
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in Shorewall log messages <b>so long</b>? I thought MAC addresses
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were only 6 bytes in length.</a><b><br>
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</b></p>
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<p align="left"><b>16. </b><a href="#faq16">Shorewall is writing <b>log messages
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all over my console</b> making it unusable!<br>
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</a></p>
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<b>17</b>.
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<a href="#faq17">How do I find out <b>why this traffic is</b>
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getting <b>logged?</b></a><br>
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<b><br>
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21. </b><a href="#faq21">I see these <b>strange log entries
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</b>occasionally; what are they?</a><br>
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<h1>STARTING AND STOPPING<br>
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</h1>
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<p align="left"><b>7. </b><a href="#faq7">When I stop Shorewall <b>using 'shorewall
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stop', I can't connect to anything</b>. Why doesn't that command
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work?</a></p>
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<p align="left"><b>8. </b><a href="#faq8">When I try to <b>start Shorewall
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on RedHat</b> I get messages about insmod failing
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-- what's wrong?<br>
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</a></p>
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<p align="left"><b>8a. </b><a href="#faq8a">When I try to <b>start Shorewall
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on RedHat</b> I get a message referring me to <b>FAQ #8</b></a><br>
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</p>
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<p align="left"><b>9. </b><a href="FAQ.htm#faq9">Why can't Shorewall <b>detect
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my interfaces </b>properly at startup?</a></p>
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<b>22. </b><a href="#faq22">I have
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some <b>iptables commands </b>that I want to <b>run when Shorewall
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starts.</b> Which file do I put them in?</a><br>
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<h1>ABOUT SHOREWALL<br>
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</h1>
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<p align="left"><b>10. </b><a href="#faq10">What <b>distributions</b> does
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it work with?</a></p>
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<p align="left"><b>11. </b><a href="#faq18">What <b>features</b> does it support?</a></p>
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<p align="left"><b>12. </b><a href="#faq12">Is there a <b>GUI?</b></a></p>
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<p align="left"><b>13. </b><a href="#faq13">Why do you call it <b>"Shorewall"?</b></a></p>
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<b>23. </b><a href="#faq23">Why do you use
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such <b>ugly fonts</b> on your <b>web site</b>?</a><br>
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<b><br>
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25. </b><a href="#faq25">How to I tell <b>which version of Shorewall</b>
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I am <b>running</b>?</a><br>
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<h1>RFC 1918<br>
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</h1>
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<p align="left"><b>14. </b><a href="#faq14">I'm connected via a cable modem
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||
and it has an internel web server that allows
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||
me to configure/monitor it but as expected if I enable
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||
<b> rfc1918 blocking</b> for my eth0 interface, it also
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blocks the <b>cable modems web server</b></a>.</p>
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<p align="left"><b>14a. </b><a href="#faq14a">Even though it assigns public
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IP addresses, my ISP's DHCP server has an RFC
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1918 address. If I enable RFC 1918 filtering on my external
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interface, <b>my DHCP client cannot renew its lease</b>.</a></p>
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<h1>ALIAS IP ADDRESSES/VIRTUAL INTERFACES<br>
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</h1>
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<b>18.</b> <a href="#faq18">Is there
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any way to use <b>aliased ip addresses</b> with Shorewall,
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and maintain separate rulesets for different IPs?</a><br>
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<h1>MISCELLANEOUS<br>
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</h1>
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<b>19. </b><a href="#faq19">I have added <b>entries to /etc/shorewall/tcrules</b>
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but they <b>don't </b>seem to <b>do anything</b>. Why?</a><br>
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<br>
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<b>20. </b><a href="#faq20">I
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have just set up a server. <b>Do I have to change Shorewall
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to allow access to my server from the internet?</b></a><br>
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<br>
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<b>24. </b><a href="#faq24">How can I <b>allow
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conections</b> to let's say the ssh port only<b> from specific
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IP Addresses</b> on the internet?</a><br>
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<br>
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<br>
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<br>
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<hr>
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<h4 align="left"><a name="faq1"></a>1. I want to forward UDP port 7777 to
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my my personal PC with IP address 192.168.1.5.
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I've looked everywhere and can't find how to do it.</h4>
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<p align="left"><b>Answer: </b>The <a
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href="Documentation.htm#PortForward"> first example</a> in the <a
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href="Documentation.htm#Rules">rules file documentation</a> shows how to
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do port forwarding under Shorewall. The format
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of a port-forwarding rule to a local system is as follows:</p>
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<blockquote>
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<table border="1" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber1" cellspacing="1">
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<tbody>
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<tr>
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<td><u><b>ACTION</b></u></td>
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<td><u><b>SOURCE</b></u></td>
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<td><u><b>DESTINATION</b></u></td>
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<td><u><b>PROTOCOL</b></u></td>
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<td><u><b>PORT</b></u></td>
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<td><u><b>SOURCE
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PORT</b></u></td>
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<td><u><b>ORIG.
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DEST.</b></u></td>
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</tr>
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<tr>
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<td>DNAT</td>
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<td>net</td>
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<td>loc:<i><local
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IP address></i>[:<i><local port</i>>]</td>
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<td><i><protocol></i></td>
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<td><i><port
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#></i></td>
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<td> <br>
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</td>
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<td> <br>
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</td>
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</tr>
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||
</tbody>
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</table>
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</blockquote>
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<p align="left">So to forward UDP port 7777 to internal system 192.168.1.5,
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the rule is:</p>
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<blockquote>
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<table border="1" cellpadding="2" style="border-collapse: collapse;"
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id="AutoNumber1" cellspacing="1">
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<tbody>
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<tr>
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<td><u><b>ACTION</b></u></td>
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<td><u><b>SOURCE</b></u></td>
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<td><u><b>DESTINATION</b></u></td>
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<td><u><b>PROTOCOL</b></u></td>
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<td><u><b>PORT</b></u></td>
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<td><u><b>SOURCE
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PORT</b></u></td>
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<td><u><b>ORIG.
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DEST.</b></u></td>
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</tr>
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<tr>
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<td>DNAT</td>
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<td>net</td>
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<td>loc:192.168.1.5</td>
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<td>udp</td>
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<td>7777</td>
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<td> <br>
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</td>
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<td> <br>
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</td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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<div align="left"> <font face="Courier"> </font>If
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you want to forward requests directed to a particular address
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( <i><external IP></i> ) on your firewall to an internal
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system:</div>
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<blockquote>
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<table border="1" cellpadding="2" cellspacing="0"
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style="border-collapse: collapse;">
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<tbody>
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<tr>
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<td><u><b>ACTION</b></u></td>
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<td><u><b>SOURCE</b></u></td>
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<td><u><b>DESTINATION</b></u></td>
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<td><u><b>PROTOCOL</b></u></td>
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<td><u><b>PORT</b></u></td>
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<td><u><b>SOURCE
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PORT</b></u></td>
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<td><u><b>ORIG.
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DEST.</b></u></td>
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</tr>
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<tr>
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<td>DNAT</td>
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<td>net</td>
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<td>loc:<i><local
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IP address></i>[:<i><local port</i>>]</td>
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<td><i><protocol></i></td>
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<td><i><port
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#></i></td>
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<td>-</td>
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<td><i><external
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IP></i></td>
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</tr>
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</tbody>
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</table>
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</blockquote>
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Finally, if you need to forward a range of ports, in
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the PORT column specify the range as <i>low-port</i>:<i>high-port</i>.<br>
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<h4 align="left"><a name="faq1a"></a>1a. Ok -- I followed those instructions
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but it doesn't work</h4>
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<p align="left"><b>Answer: </b>That is usually the result of one of three
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things:</p>
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<ul>
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<li>You are trying
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to test from inside your firewall (no, that won't
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work -- see <a href="#faq2">FAQ #2</a>).</li>
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<li>You have a
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||
more basic problem with your local system such as an
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incorrect default gateway configured (it should be set to
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the IP address of your firewall's internal interface).</li>
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<li>Your ISP is blocking that particular port inbound.<br>
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||
</li>
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</ul>
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<h4 align="left"><a name="faq1b"></a>1b. I'm still having problems with port
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forwarding</h4>
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<b>Answer: </b>To further
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||
diagnose this problem:<br>
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<ul>
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<li>As root, type "iptables
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-t nat -Z". This clears the NetFilter counters in the
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nat table.</li>
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<li>Try to connect to the
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||
redirected port from an external host.</li>
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||
<li>As root type "shorewall
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show nat"</li>
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<li>Locate the appropriate
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DNAT rule. It will be in a chain called <i><source
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||
zone></i>_dnat ('net_dnat' in the above examples).</li>
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<li>Is the packet count
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||
in the first column non-zero? If so, the connection
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||
request is reaching the firewall and is being redirected
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||
to the server. In this case, the problem is usually a missing
|
||
or incorrect default gateway setting on the server (the server's
|
||
default gateway should be the IP address of the firewall's
|
||
interface to the server).</li>
|
||
<li>If the packet count
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||
is zero:</li>
|
||
|
||
<ul>
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||
<li>the connection request
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||
is not reaching your server (possibly it is being blocked
|
||
by your ISP); or</li>
|
||
<li>you are trying to
|
||
connect to a secondary IP address on your firewall and
|
||
your rule is only redirecting the primary IP address (You need
|
||
to specify the secondary IP address in the "ORIG. DEST." column
|
||
in your DNAT rule); or</li>
|
||
<li>your DNAT rule doesn't
|
||
match the connection request in some other way. In that
|
||
case, you may have to use a packet sniffer such as tcpdump
|
||
or ethereal to further diagnose the problem.<br>
|
||
</li>
|
||
|
||
</ul>
|
||
|
||
</ul>
|
||
|
||
<h4 align="left"><a name="faq1c"></a><b>1c. </b>From the internet, I want
|
||
to connect to port 1022 on my firewall and have the firewall forward the
|
||
connection to port 22 on local system 192.168.1.3. How do I do that?</h4>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber1">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>ACTION</b></u></td>
|
||
<td><u><b>SOURCE</b></u></td>
|
||
<td><u><b>DESTINATION</b></u></td>
|
||
<td><u><b>PROTOCOL</b></u></td>
|
||
<td><u><b>PORT</b></u></td>
|
||
<td><u><b>SOURCE
|
||
PORT</b></u></td>
|
||
<td><u><b>ORIG.
|
||
DEST.</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>DNAT</td>
|
||
<td>net<br>
|
||
</td>
|
||
<td>loc:192.168.1.3:22</td>
|
||
<td>tcp</td>
|
||
<td>1022<br>
|
||
</td>
|
||
<td><br>
|
||
</td>
|
||
<td><br>
|
||
</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<h4 align="left"><a name="faq2"></a>2. I port forward www requests to www.mydomain.com
|
||
(IP 130.151.100.69) to system 192.168.1.5 in my
|
||
local network. External clients can browse http://www.mydomain.com
|
||
but internal clients can't.</h4>
|
||
|
||
<p align="left"><b>Answer: </b>I have two objections to this setup.</p>
|
||
|
||
<ul>
|
||
<li>Having an
|
||
internet-accessible server in your local network
|
||
is like raising foxes in the corner of your hen house. If
|
||
the server is compromised, there's nothing between
|
||
that server and your other internal systems. For the cost
|
||
of another NIC and a cross-over cable, you can put your
|
||
server in a DMZ such that it is isolated from your local systems
|
||
- assuming that the Server can be located near the Firewall,
|
||
of course :-)</li>
|
||
<li>The accessibility
|
||
problem is best solved using <a
|
||
href="shorewall_setup_guide.htm#DNS">Bind Version 9 "views"</a>
|
||
(or using a separate DNS server for local clients) such that www.mydomain.com
|
||
resolves to 130.141.100.69 externally and 192.168.1.5 internally.
|
||
That's what I do here at shorewall.net for my local systems
|
||
that use static NAT.</li>
|
||
|
||
</ul>
|
||
|
||
<p align="left">If you insist on an IP solution to the accessibility problem
|
||
rather than a DNS solution, then assuming that
|
||
your external interface is eth0 and your internal
|
||
interface is eth1 and that eth1 has IP address 192.168.1.254
|
||
with subnet 192.168.1.0/24.<br>
|
||
</p>
|
||
|
||
<p align="left">If you are running Shorewall 1.4.0 or earlier see <a
|
||
href="file:///Z:/Shorewall-docs/1.3/FAQ.htm#faq2">the 1.3 FAQ</a> for instructions
|
||
suitable for those releases.<br>
|
||
</p>
|
||
|
||
<p align="left">If you are running Shorewall 1.4.1 or Shorewall 1.4.1a, please
|
||
upgrade to Shorewall 1.4.2 or later.<br>
|
||
</p>
|
||
|
||
<p align="left">Otherwise:<br>
|
||
</p>
|
||
|
||
<ul>
|
||
|
||
</ul>
|
||
|
||
<ul>
|
||
|
||
</ul>
|
||
|
||
<ul>
|
||
<li>In /etc/shorewall/interfaces:</li>
|
||
|
||
</ul>
|
||
|
||
<blockquote>
|
||
<table cellpadding="2" cellspacing="0" border="1">
|
||
<tbody>
|
||
<tr>
|
||
<td valign="top">ZONE<br>
|
||
</td>
|
||
<td valign="top">INTERFACE<br>
|
||
</td>
|
||
<td valign="top">BROADCAST<br>
|
||
</td>
|
||
<td valign="top">OPTIONS<br>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td valign="top">loc<br>
|
||
</td>
|
||
<td valign="top">eth1<br>
|
||
</td>
|
||
<td valign="top">detect<br>
|
||
</td>
|
||
<td valign="top"><b>routeback<br>
|
||
</b> </td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<ul>
|
||
|
||
</ul>
|
||
|
||
<ul>
|
||
<li>In /etc/shorewall/rules: </li>
|
||
|
||
</ul>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;">
|
||
<tbody>
|
||
<tr>
|
||
<td><b>ACTION</b></td>
|
||
<td><b>SOURCE</b></td>
|
||
<td><b>DEST</b></td>
|
||
<td><b> PROTO</b></td>
|
||
<td><b>DEST<br>
|
||
PORT(S)</b></td>
|
||
<td><b>SOURCE<br>
|
||
PORT(S)</b></td>
|
||
<td><b>ORIGINAL<br>
|
||
DEST</b></td>
|
||
</tr>
|
||
<tr>
|
||
<td>DNAT<br>
|
||
</td>
|
||
<td>loc</td>
|
||
<td>web:192.168.1.5<br>
|
||
</td>
|
||
<td>tcp</td>
|
||
<td>www</td>
|
||
<td> -<br>
|
||
</td>
|
||
<td>130.151.100.69:192.168.1.254<br>
|
||
</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<div align="left">
|
||
<p align="left">That rule only works of course if you have a static external
|
||
IP address. If you have a dynamic IP address
|
||
and are running Shorewall 1.3.4 or later then include
|
||
this in /etc/shorewall/init:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<pre> ETH0_IP=`find_interface_address eth0`</pre>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">and make your DNAT rule:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber1">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>ACTION</b></u></td>
|
||
<td><u><b>SOURCE</b></u></td>
|
||
<td><u><b>DESTINATION</b></u></td>
|
||
<td><u><b>PROTOCOL</b></u></td>
|
||
<td><u><b>PORT</b></u></td>
|
||
<td><u><b>SOURCE
|
||
PORT</b></u></td>
|
||
<td><u><b>ORIG.
|
||
DEST.</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>DNAT</td>
|
||
<td>loc</td>
|
||
<td>web:192.168.1.5</td>
|
||
<td>tcp</td>
|
||
<td>www</td>
|
||
<td>-</td>
|
||
<td>$ETH0_IP:192.168.1.254</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Using this technique, you will want to configure your DHCP/PPPoE
|
||
client to automatically restart Shorewall each
|
||
time that you get a new IP address.</p>
|
||
</div>
|
||
|
||
<h4 align="left"><a name="faq2a"></a>2a. I have a zone "Z" with an RFC1918
|
||
subnet and I use static NAT to assign non-RFC1918
|
||
addresses to hosts in Z. Hosts in Z cannot communicate
|
||
with each other using their external (non-RFC1918 addresses)
|
||
so they can't access each other using their DNS names.</h4>
|
||
|
||
<p align="left"><b>Answer: </b>This is another problem that is best solved
|
||
using Bind Version 9 "views". It allows both external
|
||
and internal clients to access a NATed host using
|
||
the host's DNS name.</p>
|
||
|
||
<p align="left">Another good way to approach this problem is to switch from
|
||
static NAT to Proxy ARP. That way, the hosts in
|
||
Z have non-RFC1918 addresses and can be accessed externally
|
||
and internally using the same address. </p>
|
||
|
||
<p align="left">If you don't like those solutions and prefer routing all
|
||
Z->Z traffic through your firewall then:</p>
|
||
|
||
<p align="left">a) Set the Z->Z policy to ACCEPT.<br>
|
||
b) Masquerade Z
|
||
to itself.<br>
|
||
<br>
|
||
Example:</p>
|
||
|
||
<p align="left">Zone: dmz<br>
|
||
Interface: eth2<br>
|
||
Subnet: 192.168.2.0/24</p>
|
||
|
||
<p align="left">In /etc/shorewall/interfaces:</p>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber2">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>ZONE</b></u></td>
|
||
<td><u><b>INTERFACE</b></u></td>
|
||
<td><u><b>BROADCAST</b></u></td>
|
||
<td><u><b>OPTIONS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>dmz</td>
|
||
<td>eth2</td>
|
||
<td>192.168.2.255</td>
|
||
<td><br>
|
||
</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p align="left">In /etc/shorewall/policy:</p>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber3">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>SOURCE
|
||
</b></u></td>
|
||
<td><u><b>DESTINATION</b></u></td>
|
||
<td><u><b>POLICY</b></u></td>
|
||
<td><u><b>LIMIT:BURST</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>dmz</td>
|
||
<td>dmz</td>
|
||
<td>ACCEPT</td>
|
||
<td> <br>
|
||
</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<p align="left">In /etc/shorewall/masq:</p>
|
||
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber3" width="369">
|
||
<tbody>
|
||
<tr>
|
||
<td
|
||
width="93"><u><b>INTERFACE </b></u></td>
|
||
<td
|
||
width="31"><u><b>SUBNET</b></u></td>
|
||
<td
|
||
width="120"><u><b>ADDRESS</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td
|
||
width="93">eth2</td>
|
||
<td
|
||
width="31">192.168.2.0/24</td>
|
||
<td
|
||
width="120"> <br>
|
||
</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
|
||
<h4 align="left"><a name="faq3"></a>3. I want to use Netmeeting or MSN Instant
|
||
Messenger with Shorewall. What do I do?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>There is an <a
|
||
href="http://www.kfki.hu/%7Ekadlec/sw/netfilter/newnat-suite/"> H.323 connection
|
||
tracking/NAT module</a> that may help with Netmeeting.
|
||
Look <a href="http://linux-igd.sourceforge.net">here</a> for a
|
||
solution for MSN IM but be aware that there are significant security
|
||
risks involved with this solution. Also check the Netfilter mailing
|
||
list archives at <a href="http://www.netfilter.org">http://www.netfilter.org</a>.
|
||
</p>
|
||
|
||
<h4 align="left"><a name="faq4"></a>4. I just used an online port scanner
|
||
to check my firewall and it shows some ports
|
||
as 'closed' rather than 'blocked'. Why?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>The common.def included with version 1.3.x
|
||
always rejects connection requests on TCP port
|
||
113 rather than dropping them. This is necessary
|
||
to prevent outgoing connection problems to services
|
||
that use the 'Auth' mechanism for identifying requesting
|
||
users. Shorewall also rejects TCP ports 135, 137 and 139
|
||
as well as UDP ports 137-139. These are ports that are used
|
||
by Windows (Windows <u>can</u> be configured to use the DCE cell
|
||
locator on port 135). Rejecting these connection requests rather
|
||
than dropping them cuts down slightly on the amount of Windows chatter
|
||
on LAN segments connected to the Firewall. </p>
|
||
|
||
<p align="left">If you are seeing port 80 being 'closed', that's probably
|
||
your ISP preventing you from running a web server
|
||
in violation of your Service Agreement.</p>
|
||
|
||
<h4 align="left"><a name="faq4a"></a>4a. I just ran an nmap UDP scan of my
|
||
firewall and it showed 100s of ports as open!!!!</h4>
|
||
|
||
<p align="left"><b>Answer: </b>Take a deep breath and read the nmap man page
|
||
section about UDP scans. If nmap gets <b>nothing</b>
|
||
back from your firewall then it reports the port
|
||
as open. If you want to see which UDP ports are really
|
||
open, temporarily change your net->all policy to REJECT,
|
||
restart Shorewall and do the nmap UDP scan again.<br>
|
||
</p>
|
||
|
||
<h4><a name="faq4b"></a>4b. I have a port that I can't close no matter how
|
||
I change my rules.<2E></h4>
|
||
I had a rule that allowed telnet from my local network to my firewall; I
|
||
removed that rule and restarted Shorewall but my telnet session still works!!!<br>
|
||
<br>
|
||
<b>Answer: </b><EFBFBD>Rules only govern the establishment of new connections.
|
||
Once a connection is established through the firewall it will be usable until
|
||
disconnected (tcp) or until it times out (other protocols).<2E> If you stop telnet
|
||
and try to establish a new session your firerwall will block that attempt.<br>
|
||
|
||
<h4 align="left"><a name="faq5"></a>5. I've installed Shorewall and now I
|
||
can't ping through the firewall</h4>
|
||
|
||
<p align="left"><b>Answer: </b>If you want your firewall to be totally open
|
||
for "ping", </p>
|
||
|
||
<p align="left">a) Create /etc/shorewall/common if it doesn't already exist.
|
||
<br>
|
||
b) Be sure that
|
||
the first command in the file is ". /etc/shorewall/common.def"<br>
|
||
c) Add the following
|
||
to /etc/shorewall/common </p>
|
||
|
||
<blockquote>
|
||
<p align="left">run_iptables -A icmpdef -p ICMP --icmp-type echo-request
|
||
-j ACCEPT<br>
|
||
</p>
|
||
</blockquote>
|
||
For a complete description of Shorewall
|
||
'ping' management, see <a href="ping.html">this page</a>.
|
||
|
||
<h4 align="left"><a name="faq6"></a>6. Where are the log messages written
|
||
and how do I change the destination?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>NetFilter uses the kernel's equivalent of
|
||
syslog (see "man syslog") to log messages. It always uses the LOG_KERN (kern)
|
||
facility (see "man openlog") and you get to choose the log level (again,
|
||
see "man syslog") in your <a href="Documentation.htm#Policy">policies</a>
|
||
and <a href="Documentation.htm#Rules">rules</a>. The destination for messaged
|
||
logged by syslog is controlled by /etc/syslog.conf (see "man syslog.conf").
|
||
When you have changed /etc/syslog.conf, be sure
|
||
to restart syslogd (on a RedHat system, "service syslog
|
||
restart"). </p>
|
||
|
||
<p align="left">By default, older versions of Shorewall ratelimited log messages
|
||
through <a href="Documentation.htm#Conf">settings</a>
|
||
in /etc/shorewall/shorewall.conf -- If you want to
|
||
log all messages, set: </p>
|
||
|
||
<div align="left">
|
||
<pre align="left"> LOGLIMIT=""<br> LOGBURST=""<br></pre>
|
||
Beginning with Shorewall version 1.3.12, you can <a
|
||
href="shorewall_logging.html">set up Shorewall to log all of its messages
|
||
to a separate file</a>.<br>
|
||
</div>
|
||
|
||
<h4 align="left"><a name="faq6a"></a>6a. Are there any log parsers that work
|
||
with Shorewall?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>Here are several links that may be helpful:
|
||
</p>
|
||
|
||
<blockquote>
|
||
<p align="left"><a
|
||
href="http://www.shorewall.net/pub/shorewall/parsefw/"> http://www.shorewall.net/pub/shorewall/parsefw/</a><br>
|
||
<a
|
||
href="http://www.fireparse.com">http://www.fireparse.com</a><br>
|
||
<a
|
||
href="http://cert.uni-stuttgart.de/projects/fwlogwatch">http://cert.uni-stuttgart.de/projects/fwlogwatch</a><a
|
||
href="http://www.logwatch.org"><br>
|
||
http://www.logwatch.org</a><br>
|
||
<a href="http://gege.org/iptables">http://gege.org/iptables</a><br>
|
||
</p>
|
||
</blockquote>
|
||
I personnaly use Logwatch. It emails
|
||
me a report each day from my various systems with each report
|
||
summarizing the logged activity on the corresponding system.
|
||
|
||
<h4 align="left"><b><a name="faq6b"></a>6b. DROP messages</b> on port 10619
|
||
are <b>flooding the logs</b> with their connect requests. Can
|
||
i exclude these error messages for this port temporarily from logging
|
||
in Shorewall?</h4>
|
||
Temporarily add the following rule:<br>
|
||
|
||
<pre> DROP net fw udp 10619</pre>
|
||
|
||
<h4 align="left"><a name="faq6c"></a>6c. All day long I get a steady flow
|
||
of these DROP messages from port 53 to some high numbered port.
|
||
They get dropped, but what the heck are they?</h4>
|
||
|
||
<pre>Jan 8 15:50:48 norcomix kernel: Shorewall:net2all:DROP:IN=eth0 OUT= MAC=00:40:c7:2e:09:c0:00:01:64:4a:70:00:08:00<br> SRC=208.138.130.16 DST=24.237.22.45 LEN=53 TOS=0x00 PREC=0x00<br> TTL=251 ID=8288 DF PROTO=UDP SPT=53 DPT=40275 LEN=33 </pre>
|
||
<b>Answer: </b>There are two possibilities:<br>
|
||
|
||
<ol>
|
||
<li>They are late-arriving replies to DNS queries.</li>
|
||
<li>They are corrupted reply packets.</li>
|
||
|
||
</ol>
|
||
You can distinguish the difference by setting the
|
||
<b>logunclean</b> option (<a
|
||
href="Documentation.htm#Interfaces">/etc/shorewall/interfaces</a>)
|
||
on your external interface (eth0 in the above example). If they get
|
||
logged twice, they are corrupted. I solve this problem by using
|
||
an /etc/shorewall/common file like this:<br>
|
||
|
||
<blockquote>
|
||
<pre>#<br># Include the standard common.def file<br>#<br>. /etc/shorewall/common.def<br>#<br># The following rule is non-standard and compensates for tardy<br># DNS replies<br>#<br>run_iptables -A common -p udp --sport 53 -mstate --state NEW -j DROP</pre>
|
||
</blockquote>
|
||
The above file is also include in all of my sample
|
||
configurations available in the <a
|
||
href="shorewall_quickstart_guide.htm">Quick Start Guides</a> and in
|
||
the common.def file in Shorewall 1.4.0 and later.<br>
|
||
|
||
<h4 align="left"><a name="faq6d"></a><b>6d.</b> Why is the MAC address in
|
||
Shorewall log messages so long? I thought MAC addresses were only
|
||
6 bytes in length.</h4>
|
||
What is labeled as the MAC address in a Shorewall log message
|
||
is actually the Ethernet frame header. IT contains:<br>
|
||
|
||
<ul>
|
||
<li>the destination MAC address (6 bytes)</li>
|
||
<li>the source MAC address (6 bytes)</li>
|
||
<li>the ethernet frame type (2 bytes)</li>
|
||
|
||
</ul>
|
||
Example:<br>
|
||
<br>
|
||
MAC=00:04:4c:dc:e2:28:00:b0:8e:cf:3c:4c:08:00<br>
|
||
|
||
<ul>
|
||
<li>Destination MAC address = 00:04:4c:dc:e2:28</li>
|
||
<li>Source MAC address = 00:b0:8e:cf:3c:4c</li>
|
||
<li>Ethernet Frame Type = 08:00 (IP Version 4)</li>
|
||
|
||
</ul>
|
||
|
||
<h4 align="left"><a name="faq7"></a>7. When I stop Shorewall using 'shorewall
|
||
stop', I can't connect to anything. Why doesn't
|
||
that command work?</h4>
|
||
|
||
<p align="left">The 'stop' command is intended to place your firewall into
|
||
a safe state whereby only those hosts listed in
|
||
/etc/shorewall/routestopped' are activated. If
|
||
you want to totally open up your firewall, you must use the
|
||
'shorewall clear' command. </p>
|
||
|
||
<h4 align="left"><a name="faq8"></a>8. When I try to start Shorewall on RedHat,
|
||
I get messages about insmod failing -- what's wrong?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>The output you will see looks something like
|
||
this:</p>
|
||
|
||
<pre> /lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: init_module: Device or resource busy<br> Hint: insmod errors can be caused by incorrect module parameters, including invalid IO or IRQ parameters<br> /lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: insmod<br> /lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o failed<br> /lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: insmod ip_tables failed<br> iptables v1.2.3: can't initialize iptables table `nat': iptables who? (do you need to insmod?)<br> Perhaps iptables or your kernel needs to be upgraded.</pre>
|
||
|
||
<p align="left">This is usually cured by the following sequence of commands:
|
||
</p>
|
||
|
||
<div align="left">
|
||
<pre align="left"> <b><font color="#009900">service ipchains stop<br> chkconfig --delete ipchains<br> rmmod ipchains</font></b></pre>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Also, be sure to check the <a href="errata.htm">errata</a>
|
||
for problems concerning the version of iptables
|
||
(v1.2.3) shipped with RH7.2.<br>
|
||
</p>
|
||
|
||
<h4><a name="faq8a"></a><b>8a. </b>When I try to start Shorewall on RedHat
|
||
I get a message referring me to FAQ #8</h4>
|
||
<b>Answer:</b> This is usually cured by the sequence of commands
|
||
shown above in FAQ #8
|
||
</div>
|
||
|
||
<h4 align="left"><a name="faq9"></a>9. Why can't Shorewall detect my interfaces
|
||
properly at startup?</h4>
|
||
|
||
<p align="left">I just installed Shorewall and when I issue the start command,
|
||
I see the following:</p>
|
||
|
||
<div align="left">
|
||
<pre> Processing /etc/shorewall/params ...<br> Processing /etc/shorewall/shorewall.conf ...<br> Starting Shorewall...<br> Loading Modules...<br> Initializing...<br> Determining Zones...<br> Zones: net loc<br> Validating interfaces file...<br> Validating hosts file...<br> Determining Hosts in Zones...<br><b> Net Zone: eth0:0.0.0.0/0<br> Local Zone: eth1:0.0.0.0/0<br></b> Deleting user chains...<br> Creating input Chains...<br> ...</pre>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Why can't Shorewall detect my interfaces properly?</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left"><b>Answer: </b>The above output is perfectly normal. The
|
||
Net zone is defined as all hosts that are connected through eth0 and the
|
||
local zone is defined as all hosts connected through eth1</p>
|
||
</div>
|
||
|
||
<h4 align="left"><a name="faq10"></a>10. What Distributions does it work
|
||
with?</h4>
|
||
|
||
<p align="left">Shorewall works with any GNU/Linux distribution that includes
|
||
the <a
|
||
href="shorewall_prerequisites.htm">proper prerequisites</a>.</p>
|
||
|
||
<h4 align="left">11. What Features does it have?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>See the <a href="shorewall_features.htm">Shorewall
|
||
Feature List</a>.</p>
|
||
|
||
<h4 align="left"><a name="faq12"></a>12. Is there a GUI?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>Yes. Shorewall support is included in Webmin
|
||
1.060 and later versions. See <a href="http://www.webmin.com">http://www.webmin.com</a>
|
||
</p>
|
||
|
||
<h4 align="left"> <a name="faq13"></a>13. Why do you call it "Shorewall"?</h4>
|
||
|
||
<p align="left"><b>Answer: </b>Shorewall is a concatenation of "<u>Shore</u>line"
|
||
(<a href="http://www.cityofshoreline.com">the
|
||
city where I live</a>) and "Fire<u>wall</u>". The full
|
||
name of the product is actually "Shoreline Firewall" but "Shorewall"
|
||
is must more commonly used.</p>
|
||
|
||
<h4 align="left"> <a name="faq14"></a>14. I'm connected via a cable modem
|
||
and it has an internal web server that allows
|
||
me to configure/monitor it but as expected if I enable
|
||
rfc1918 blocking for my eth0 interface (the internet one),
|
||
it also blocks the cable modems web server.</h4>
|
||
|
||
<p align="left">Is there any way it can add a rule before the rfc1918 blocking
|
||
that will let all traffic to and from the 192.168.100.1
|
||
address of the modem in/out but still block all other
|
||
rfc1918 addresses?</p>
|
||
|
||
<p align="left"><b>Answer: </b>If you are running a version of Shorewall
|
||
earlier than 1.3.1, create /etc/shorewall/start and in it, place the
|
||
following:</p>
|
||
|
||
<div align="left">
|
||
<pre> run_iptables -I rfc1918 -s 192.168.100.1 -j ACCEPT</pre>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">If you are running version 1.3.1 or later, simply add the
|
||
following to<a
|
||
href="Documentation.htm#rfc1918"> /etc/shorewall/rfc1918</a>:</p>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<blockquote>
|
||
<table border="1" cellpadding="2" style="border-collapse: collapse;"
|
||
id="AutoNumber3">
|
||
<tbody>
|
||
<tr>
|
||
<td><u><b>SUBNET
|
||
</b></u></td>
|
||
<td><u><b>TARGET</b></u></td>
|
||
</tr>
|
||
<tr>
|
||
<td>192.168.100.1</td>
|
||
<td>RETURN</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">Be sure that you add the entry ABOVE the entry for 192.168.0.0/16.<br>
|
||
</p>
|
||
|
||
<p align="left">Note: If you add a second IP address to your external firewall
|
||
interface to correspond to the modem address, you
|
||
must also make an entry in /etc/shorewall/rfc1918 for
|
||
that address. For example, if you configure the address
|
||
192.168.100.2 on your firewall, then you would add two entries
|
||
to /etc/shorewall/rfc1918: <br>
|
||
</p>
|
||
|
||
<blockquote>
|
||
<table cellpadding="2" border="1" style="border-collapse: collapse;">
|
||
<tbody>
|
||
<tr>
|
||
<td
|
||
valign="top"><u><b>SUBNET</b></u><br>
|
||
</td>
|
||
<td
|
||
valign="top"><u><b>TARGET</b></u><br>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td
|
||
valign="top">192.168.100.1<br>
|
||
</td>
|
||
<td
|
||
valign="top">RETURN<br>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td
|
||
valign="top">192.168.100.2<br>
|
||
</td>
|
||
<td
|
||
valign="top">RETURN<br>
|
||
</td>
|
||
</tr>
|
||
|
||
</tbody>
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<h4 align="left"><a name="faq14a"></a>14a. Even though it assigns public
|
||
IP addresses, my ISP's DHCP server has an RFC 1918 address. If I enable
|
||
RFC 1918 filtering on my external interface, my DHCP client cannot renew
|
||
its lease.</h4>
|
||
</div>
|
||
|
||
<div align="left">
|
||
<p align="left">The solution is the same as FAQ 14 above. Simply substitute
|
||
the IP address of your ISPs DHCP server.</p>
|
||
</div>
|
||
|
||
<h4 align="left"><a name="faq15"></a>15. My local systems can't see out to
|
||
the net</h4>
|
||
|
||
<p align="left"><b>Answer: </b>Every time I read "systems can't see out to
|
||
the net", I wonder where the poster bought computers
|
||
with eyes and what those computers will "see" when
|
||
things are working properly. That aside, the most common
|
||
causes of this problem are:</p>
|
||
|
||
<ol>
|
||
<li>
|
||
|
||
<p align="left">The default gateway on each local system isn't set to
|
||
the IP address of the local firewall interface.</p>
|
||
</li>
|
||
<li>
|
||
|
||
<p align="left">The entry for the local network in the /etc/shorewall/masq
|
||
file is wrong or missing.</p>
|
||
</li>
|
||
<li>
|
||
|
||
<p align="left">The DNS settings on the local systems are wrong or the
|
||
user is running a DNS server on the firewall
|
||
and hasn't enabled UDP and TCP port 53 from the
|
||
firewall to the internet.</p>
|
||
</li>
|
||
|
||
</ol>
|
||
|
||
<h4 align="left"><a name="faq16"></a>16. Shorewall is writing log messages
|
||
all over my console making it unusable!</h4>
|
||
|
||
<p align="left"><b>Answer: </b>"man dmesg" -- add a suitable 'dmesg' command
|
||
to your startup scripts or place it in /etc/shorewall/start.
|
||
Under RedHat, the max log level that is sent to
|
||
the console is specified in /etc/sysconfig/init in the
|
||
LOGLEVEL variable.<br>
|
||
</p>
|
||
|
||
<h4><a name="faq17"></a>17. How do I find out why this traffic is getting
|
||
logged?</h4>
|
||
<b>Answer: </b>Logging
|
||
occurs out of a number of chains (as indicated in
|
||
the log message) in Shorewall:<br>
|
||
|
||
<ol>
|
||
<li><b>man1918 - </b>The
|
||
destination address is listed in /etc/shorewall/rfc1918
|
||
with a <b>logdrop </b>target -- see <a
|
||
href="Documentation.htm#rfc1918">/etc/shorewall/rfc1918.</a></li>
|
||
<li><b>rfc1918</b>
|
||
- The source address is listed in /etc/shorewall/rfc1918
|
||
with a <b>logdrop </b>target -- see <a
|
||
href="Documentation.htm#rfc1918">/etc/shorewall/rfc1918.</a></li>
|
||
<li><b>all2<zone></b>,
|
||
<b><zone>2all</b> or <b>all2all </b>-
|
||
You have a<a href="Documentation.htm#Policy"> policy</a> that specifies
|
||
a log level and this packet is being logged under that policy.
|
||
If you intend to ACCEPT this traffic then you need a <a
|
||
href="Documentation.htm#Rules">rule</a> to that effect.<br>
|
||
</li>
|
||
<li><b><zone1>2<zone2>
|
||
</b>- Either you have a<a
|
||
href="Documentation.htm#Policy"> policy</a> for <b><zone1>
|
||
</b>to <b><zone2></b> that specifies a log level and
|
||
this packet is being logged under that policy or this packet
|
||
matches a <a href="Documentation.htm#Rules">rule</a> that includes
|
||
a log level.</li>
|
||
<li><b><interface>_mac</b>
|
||
- The packet is being logged under the <b>maclist</b>
|
||
<a href="Documentation.htm#Interfaces">interface option</a>.<br>
|
||
</li>
|
||
<li><b>logpkt</b> -
|
||
The packet is being logged under the <b>logunclean</b>
|
||
<a href="Documentation.htm#Interfaces">interface option</a>.</li>
|
||
<li><b>badpkt </b>-
|
||
The packet is being logged under the <b>dropunclean</b>
|
||
<a href="Documentation.htm#Interfaces">interface option</a>
|
||
as specified in the <b>LOGUNCLEAN </b>setting in <a
|
||
href="Documentation.htm#Conf">/etc/shorewall/shorewall.conf</a>.</li>
|
||
<li><b>blacklst</b>
|
||
- The packet is being logged because the source IP
|
||
is blacklisted in the<a href="Documentation.htm#Blacklist"> /etc/shorewall/blacklist
|
||
</a>file.</li>
|
||
<li><b>newnotsyn </b>-
|
||
The packet is being logged because it is a TCP packet
|
||
that is not part of any current connection yet it is not a
|
||
syn packet. Options affecting the logging of such packets include
|
||
<b>NEWNOTSYN </b>and <b>LOGNEWNOTSYN </b>in
|
||
<a href="Documentation.htm#Conf">/etc/shorewall/shorewall.conf.</a></li>
|
||
<li><b>INPUT</b> or
|
||
<b>FORWARD</b> - The packet has a source IP address
|
||
that isn't in any of your defined zones ("shorewall check"
|
||
and look at the printed zone definitions) or the chain is FORWARD
|
||
and the destination IP isn't in any of your defined zones.</li>
|
||
<li><b>logflags </b>- The packet
|
||
is being logged because it failed the checks implemented
|
||
by the <b>tcpflags </b><a
|
||
href="Documentation.htm#Interfaces">interface option</a>.<br>
|
||
</li>
|
||
|
||
</ol>
|
||
|
||
<h4><a name="faq18"></a>18. Is there any way to use <b>aliased ip addresses</b>
|
||
with Shorewall, and maintain separate rulesets for
|
||
different IPs?</h4>
|
||
<b>Answer: </b>Yes. See <a
|
||
href="Shorewall_and_Aliased_Interfaces.html">Shorewall and Aliased Interfaces</a>.
|
||
|
||
<h4><b><a name="faq19"></a>19. </b>I have added entries to /etc/shorewall/tcrules
|
||
but they don't seem to do anything. Why?</h4>
|
||
You probably haven't set TC_ENABLED=Yes
|
||
in /etc/shorewall/shorewall.conf so the contents of the
|
||
tcrules file are simply being ignored.<br>
|
||
|
||
<h4><a name="faq20"></a><b>20. </b>I have just set up a server. <b>Do I have
|
||
to change Shorewall to allow access to my server from
|
||
the internet?</b><br>
|
||
</h4>
|
||
Yes. Consult the <a
|
||
href="shorewall_quickstart_guide.htm">QuickStart guide</a> that you
|
||
used during your initial setup for information about how to set up
|
||
rules for your server.<br>
|
||
|
||
<h4><a name="faq21"></a><b>21. </b>I see these <b>strange log entries </b>occasionally;
|
||
what are they?<br>
|
||
</h4>
|
||
|
||
<blockquote>
|
||
<pre>Nov 25 18:58:52 linux kernel: Shorewall:net2all:DROP:IN=eth1 OUT= MAC=00:60:1d:f0:a6:f9:00:60:1d:f6:35:50:08:00<br> SRC=206.124.146.179 DST=192.0.2.3 LEN=56 TOS=0x00 PREC=0x00 TTL=110 ID=18558 PROTO=ICMP TYPE=3 CODE=3 <br> [SRC=192.0.2.3 DST=172.16.1.10 LEN=128 TOS=0x00 PREC=0x00 TTL=47 ID=0 DF PROTO=UDP SPT=53 DPT=2857 LEN=108 ]<br></pre>
|
||
</blockquote>
|
||
192.0.2.3 is external on my firewall...
|
||
172.16.0.0/24 is my internal LAN<br>
|
||
<br>
|
||
<b>Answer: </b>While most people
|
||
associate the Internet Control Message Protocol (ICMP)
|
||
with 'ping', ICMP is a key piece of the internet. ICMP is
|
||
used to report problems back to the sender of a packet; this is
|
||
what is happening here. Unfortunately, where NAT is involved (including
|
||
SNAT, DNAT and Masquerade), there are a lot of broken implementations.
|
||
That is what you are seeing with these messages.<br>
|
||
<br>
|
||
Here is my interpretation of what
|
||
is happening -- to confirm this analysis, one would have to
|
||
have packet sniffers placed a both ends of the connection.<br>
|
||
<br>
|
||
Host 172.16.1.10 behind NAT gateway
|
||
206.124.146.179 sent a UDP DNS query to 192.0.2.3 and your
|
||
DNS server tried to send a response (the response information
|
||
is in the brackets -- note source port 53 which marks this as a
|
||
DNS reply). When the response was returned to to 206.124.146.179,
|
||
it rewrote the destination IP TO 172.16.1.10 and forwarded the packet
|
||
to 172.16.1.10 who no longer had a connection on UDP port 2857.
|
||
This causes a port unreachable (type 3, code 3) to be generated back
|
||
to 192.0.2.3. As this packet is sent back through 206.124.146.179,
|
||
that box correctly changes the source address in the packet to 206.124.146.179
|
||
but doesn't reset the DST IP in the original DNS response similarly.
|
||
When the ICMP reaches your firewall (192.0.2.3), your firewall has
|
||
no record of having sent a DNS reply to 172.16.1.10 so this ICMP doesn't
|
||
appear to be related to anything that was sent. The final result
|
||
is that the packet gets logged and dropped in the all2all chain. I have
|
||
also seen cases where the source IP in the ICMP itself isn't set back
|
||
to the external IP of the remote NAT gateway; that causes your firewall
|
||
to log and drop the packet out of the rfc1918 chain because the source
|
||
IP is reserved by RFC 1918.<br>
|
||
|
||
<h4><a name="faq22"></a><b>22. </b>I have some <b>iptables commands </b>that
|
||
I want to <b>run when Shorewall starts.</b> Which file do
|
||
I put them in?</h4>
|
||
You can place these commands in
|
||
one of the <a href="shorewall_extension_scripts.htm">Shorewall Extension
|
||
Scripts</a>. Be sure that you look at the contents of the chain(s) that
|
||
you will be modifying with your commands to be sure that the
|
||
commands will do what they are intended. Many iptables commands
|
||
published in HOWTOs and other instructional material use the -A
|
||
command which adds the rules to the end of the chain. Most chains
|
||
that Shorewall constructs end with an unconditional DROP, ACCEPT or
|
||
REJECT rule and any rules that you add after that will be ignored.
|
||
Check "man iptables" and look at the -I (--insert) command.<br>
|
||
|
||
<h4><a name="faq23"></a><b>23. </b>Why do you use such ugly fonts on your
|
||
web site?</h4>
|
||
The Shorewall web site is almost font neutral
|
||
(it doesn't explicitly specify fonts except on a few pages)
|
||
so the fonts you see are largely the default fonts configured in
|
||
your browser. If you don't like them then reconfigure your browser.<br>
|
||
|
||
<h4><a name="faq24"></a>24. How can I <b>allow conections</b> to let's say
|
||
the ssh port only<b> from specific IP Addresses</b> on the internet?</h4>
|
||
In the SOURCE column of the rule, follow "net"
|
||
by a colon and a list of the host/subnet addresses as a comma-separated
|
||
list.<br>
|
||
|
||
<pre> net:<ip1>,<ip2>,...<br></pre>
|
||
Example:<br>
|
||
|
||
<pre> ACCEPT net:192.0.2.16/28,192.0.2.44 fw tcp 22<br></pre>
|
||
|
||
<div align="left"> </div>
|
||
|
||
<h4><b><a name="faq25"></a>25. </b>How to I tell <b>which version of Shorewall</b>
|
||
I am <b>running</b>?<br>
|
||
</h4>
|
||
At the shell prompt, type:<br>
|
||
<br>
|
||
<font color="#009900"><b> /sbin/shorewall version</b></font><br>
|
||
<br>
|
||
<font size="2">Last updated 4/14/2003 - <a
|
||
href="support.htm">Tom Eastep</a></font>
|
||
<p><a href="copyright.htm"><font size="2">Copyright</font> <20> <font
|
||
size="2">2001, 2002, 2003 Thomas M. Eastep.</font></a><br>
|
||
</p>
|
||
<br>
|
||
<br>
|
||
<br>
|
||
</body>
|
||
</html>
|