forked from extern/shorewall_code
5f9ff7336a
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@463 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
1308 lines
76 KiB
HTML
1308 lines
76 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
||
<html>
|
||
<head>
|
||
|
||
|
||
|
||
<meta http-equiv="Content-Language" content="en-us">
|
||
|
||
|
||
|
||
<meta http-equiv="Content-Type"
|
||
content="text/html; charset=windows-1252">
|
||
|
||
|
||
|
||
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
|
||
|
||
|
||
|
||
<meta name="ProgId" content="FrontPage.Editor.Document">
|
||
<title>Shorewall FAQ</title>
|
||
|
||
|
||
|
||
|
||
|
||
<meta name="Microsoft Theme" content="none">
|
||
</head>
|
||
<body>
|
||
|
||
|
||
<table border="0" cellpadding="0" cellspacing="0"
|
||
style="border-collapse: collapse;" width="100%" id="AutoNumber4"
|
||
bgcolor="#400169" height="90">
|
||
<tbody>
|
||
<tr>
|
||
<td width="100%">
|
||
|
||
|
||
|
||
|
||
<h1 align="center"><font color="#ffffff">Shorewall FAQs</font></h1>
|
||
</td>
|
||
</tr>
|
||
|
||
|
||
|
||
</tbody>
|
||
</table>
|
||
|
||
|
||
<p align="left"><b>1. </b><a href="#faq1"> I want to <b>forward</b> UDP <b>
|
||
port</b> 7777 to my my personal PC with IP address 192.168.1.5.
|
||
I've looked everywhere and can't find <b>how to do it</b>.</a></p>
|
||
|
||
|
||
<p align="left"><b>1a. </b><a href="#faq1a">Ok -- I followed those instructions
|
||
but it doesn't work.<br>
|
||
</a></p>
|
||
|
||
|
||
<p align="left"><b>1b. </b><a href="#faq1b">I'm still having problems with
|
||
port forwarding</a></p>
|
||
|
||
<p align="left"><b>2.</b> <a href="#faq2">I <b>port forward</b> www requests
|
||
to www.mydomain.com (IP 130.151.100.69) to system 192.168.1.5
|
||
in my local network. <b>External clients can browse</b>
|
||
http://www.mydomain.com but <b>internal clients can't</b>.</a></p>
|
||
|
||
|
||
<p align="left"><b>2a. </b><a href="#faq3">I have a zone "Z" with an RFC1918
|
||
subnet and I use <b>static NAT</b> 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 <b>can't access each other using their DNS names.</b></a></p>
|
||
|
||
|
||
<p align="left"><b>3. </b><a href="#faq3">I want to use <b>Netmeeting</b>
|
||
or <b>MSN Instant Messenger </b>with Shorewall. What
|
||
do I do?</a></p>
|
||
|
||
|
||
<p align="left"><b>4. </b><a href="#faq4">I just used an online port scanner
|
||
to check my firewall and it shows <b>some ports as
|
||
'closed' rather than 'blocked'.</b> Why?</a></p>
|
||
|
||
|
||
<p align="left"><b>4a. </b><a href="#faq4a">I just ran an <b>nmap UDP scan</b>
|
||
of my firewall and it showed 100s of ports as open!!!!</a></p>
|
||
|
||
|
||
<p align="left"><b>5. </b><a href="#faq5">I've installed Shorewall and now
|
||
I <b> can't ping</b> through the firewall</a></p>
|
||
|
||
|
||
<p align="left"><b>6. </b><a href="#faq6">Where are the <b>log messages</b>
|
||
written and how do I <b>change the destination</b>?</a></p>
|
||
|
||
|
||
|
||
<p align="left"><b>6a. </b><a href="#faq6a">Are there any <b>log parsers</b>
|
||
that work with Shorewall?</a></p>
|
||
|
||
<p align="left"><b>6b. <a href="#faq6b">DROP messages</a></b><a
|
||
href="#faq6b"> 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?</a><br>
|
||
</p>
|
||
|
||
<p align="left"><b>6c. </b><a href="#faq6c">All day long I get a steady flow
|
||
of these <b>DROP messages from port 53</b> <b>to some high numbered port</b>.
|
||
They get dropped, but what the heck are they?</a><br>
|
||
</p>
|
||
|
||
<p align="left"><b>6d.</b> <a href="#faq6d">Why is the <b>MAC address</b>
|
||
in Shorewall log messages <b>so long</b>? I thought MAC addresses were only
|
||
6 bytes in length.</a><b><br>
|
||
</b></p>
|
||
|
||
<p align="left"><b>7. </b><a href="#faq7">When I stop Shorewall <b>using
|
||
'shorewall stop', I can't connect to anything</b>. Why doesn't that command
|
||
work?</a></p>
|
||
|
||
|
||
<p align="left"><b>8. </b><a href="#faq8">When I try to <b>start Shorewall
|
||
on RedHat</b> I get messages about insmod failing --
|
||
what's wrong?</a></p>
|
||
|
||
|
||
<p align="left"><b>9. </b><a href="FAQ.htm#faq9">Why can't Shorewall <b>detect
|
||
my interfaces </b>properly?</a></p>
|
||
|
||
|
||
<p align="left"><b>10. </b><a href="#faq10">What <b>distributions</b> does
|
||
it work with?</a></p>
|
||
|
||
|
||
<p align="left"><b>11. </b><a href="#faq18">What <b>features</b> does it
|
||
support?</a></p>
|
||
|
||
|
||
<p align="left"><b>12. </b><a href="#faq12">Is there a <b>GUI?</b></a></p>
|
||
|
||
|
||
<p align="left"><b>13. </b><a href="#faq13">Why do you call it <b>"Shorewall"?</b></a></p>
|
||
|
||
|
||
<p align="left"><b>14. </b><a href="#faq14">I'm connected via a cable modem
|
||
and it has an internel web server that allows me to
|
||
configure/monitor it but as expected if I enable <b> rfc1918
|
||
blocking</b> for my eth0 interface, it also blocks the <b>cable
|
||
modems web server</b></a>.</p>
|
||
|
||
|
||
<p align="left"><b>14a. </b><a href="#faq14a">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, <b>my DHCP client cannot renew its lease</b>.</a></p>
|
||
|
||
|
||
<p align="left"><b>15. </b><a href="#faq15"><b>My local systems can't see
|
||
out to the net</b></a></p>
|
||
|
||
|
||
<p align="left"><b>16. </b><a href="#faq16">Shorewall is writing <b>log messages
|
||
all over my console</b> making it unusable!<br>
|
||
</a></p>
|
||
<b>17</b>. <a
|
||
href="#faq17">How do I find out <b>why this traffic is</b> getting
|
||
<b>logged?</b></a><br>
|
||
<br>
|
||
<b>18.</b> <a href="#faq18">Is there any
|
||
way to use <b>aliased ip addresses</b> with Shorewall, and
|
||
maintain separate rulesets for different IPs?</a><br>
|
||
<br>
|
||
<b>19. </b><a href="#faq19">I have added <b>entries
|
||
to /etc/shorewall/tcrules</b> but they <b>don't </b>seem to <b>do
|
||
anything</b>. Why?</a><br>
|
||
<br>
|
||
<b>20. </b><a href="#faq20">I have just set
|
||
up a server. <b>Do I have to change Shorewall to allow access
|
||
to my server from the internet?<br>
|
||
<br>
|
||
</b></a><b>21. </b><a href="#faq21">I see these <b>strange
|
||
log entries </b>occasionally; what are they?<br>
|
||
</a><br>
|
||
<b>22. </b><a href="#faq22">I have some <b>iptables commands
|
||
</b>that I want to <b>run when Shorewall starts.</b> Which file do
|
||
I put them in?</a><br>
|
||
<br>
|
||
<b>23. </b><a href="#faq23">Why do you use such <b>ugly
|
||
fonts</b> on your <b>web site</b>?</a><br>
|
||
<br>
|
||
<b>24. </b><a href="#faq24">How can I <b>allow conections</b>
|
||
to let's say the ssh port only<b> from specific IP Addresses</b> on
|
||
the internet?</a><br>
|
||
<br>
|
||
<b>25. </b><a href="#faq25">How to I tell <b>which version of Shorewall</b>
|
||
I am <b>running</b>?</a><br>
|
||
<br>
|
||
|
||
<hr>
|
||
<h4 align="left"><a name="faq1"></a>1. I want to forward UDP port 7777 to
|
||
my my personal PC with IP address 192.168.1.5. I've
|
||
looked everywhere and can't find how to do it.</h4>
|
||
|
||
|
||
<p align="left"><b>Answer: </b>The <a
|
||
href="Documentation.htm#PortForward"> first example</a> in the <a
|
||
href="Documentation.htm#Rules">rules file documentation</a> shows how to
|
||
do port forwarding under Shorewall. The format of a
|
||
port-forwarding rule to a local system is as follows:</p>
|
||
|
||
|
||
<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</td>
|
||
<td>loc:<i><local IP
|
||
address></i>[:<i><local port</i>>]</td>
|
||
<td><i><protocol></i></td>
|
||
<td><i><port #></i></td>
|
||
<td> <br>
|
||
</td>
|
||
<td> <br>
|
||
</td>
|
||
</tr>
|
||
|
||
|
||
|
||
|
||
</tbody>
|
||
|
||
</table>
|
||
</blockquote>
|
||
|
||
|
||
<p align="left">So to forward UDP port 7777 to internal system 192.168.1.5,
|
||
the rule is:</p>
|
||
|
||
|
||
<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</td>
|
||
<td>loc:192.168.1.5</td>
|
||
<td>udp</td>
|
||
<td>7777</td>
|
||
<td> <br>
|
||
</td>
|
||
<td> <br>
|
||
</td>
|
||
</tr>
|
||
|
||
|
||
|
||
|
||
</tbody>
|
||
|
||
</table>
|
||
</blockquote>
|
||
|
||
|
||
<div align="left"> <font face="Courier"> </font>If
|
||
you want to forward requests directed to a particular address (
|
||
<i><external IP></i> ) on your firewall to an internal system:</div>
|
||
|
||
|
||
<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</td>
|
||
<td>loc:<i><local IP
|
||
address></i>[:<i><local port</i>>]</td>
|
||
<td><i><protocol></i></td>
|
||
<td><i><port #></i></td>
|
||
<td>-</td>
|
||
<td><i><external IP></i></td>
|
||
</tr>
|
||
|
||
|
||
|
||
|
||
</tbody>
|
||
|
||
</table>
|
||
</blockquote>
|
||
|
||
Finally, if you need to forward a range of ports, in the PORT column
|
||
specify the range as <i>low-port</i>:<i>high-port</i>.<br>
|
||
|
||
<h4 align="left"><a name="faq1a"></a>1a. Ok -- I followed those instructions
|
||
but it doesn't work</h4>
|
||
|
||
|
||
<p align="left"><b>Answer: </b>That is usually the result of one of two things:</p>
|
||
|
||
|
||
<ul>
|
||
<li>You are trying to test from
|
||
inside your firewall (no, that won't work -- see <a
|
||
href="#faq2">FAQ #2</a>).</li>
|
||
<li>You have a more basic problem
|
||
with your local system such as an incorrect default gateway
|
||
configured (it should be set to the IP address of your
|
||
firewall's internal interface).</li>
|
||
|
||
|
||
</ul>
|
||
|
||
|
||
<h4 align="left"><a name="faq1b"></a>1b. I'm still having problems with port
|
||
forwarding</h4>
|
||
<b>Answer: </b>To further diagnose this
|
||
problem:<br>
|
||
|
||
<ul>
|
||
<li>As root, type "iptables -t nat -Z".
|
||
This clears the NetFilter counters in the nat table.</li>
|
||
<li>Try to connect to the redirected port
|
||
from an external host.</li>
|
||
<li>As root type "shorewall show nat"</li>
|
||
<li>Locate the appropriate DNAT rule.
|
||
It will be in a chain called <i><source zone></i>_dnat
|
||
('net_dnat' in the above examples).</li>
|
||
<li>Is the packet count in the first column
|
||
non-zero? If so, the connection request is reaching the firewall
|
||
and is being redirected 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 is zero:</li>
|
||
|
||
|
||
<ul>
|
||
<li>the connection request 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="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, in /etc/shorewall/rules, add:</p>
|
||
|
||
|
||
<div align="left">
|
||
</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:192.168.1.0/24</td>
|
||
<td>loc:192.168.1.5</td>
|
||
<td>tcp</td>
|
||
<td>www</td>
|
||
<td>-</td>
|
||
<td>130.151.100.69:192.168.1.254</td>
|
||
</tr>
|
||
|
||
|
||
|
||
|
||
</tbody>
|
||
|
||
</table>
|
||
</blockquote>
|
||
</div>
|
||
|
||
|
||
<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/params:</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:192.168.1.0/24</td>
|
||
<td>loc: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.</p>
|
||
|
||
|
||
<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><br>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></pre>
|
||
</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. What is labeled as the MAC address in a Shorewall log message
|
||
is actually the Ethernet frame header. In contains:<br>
|
||
</h4>
|
||
|
||
<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"> service ipchains stop<br> chkconfig --delete ipchains<br> rmmod ipchains</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.</p>
|
||
</div>
|
||
|
||
|
||
<h4 align="left"> </h4>
|
||
|
||
|
||
<h4 align="left"><a name="faq9"></a>9. Why can't Shorewall detect my interfaces
|
||
properly?</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/shorewall.conf ...<br> Processing /etc/shorewall/params ...<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. You simply use the
|
||
IP address in your rules (or if you use NAT, use the local
|
||
IP address in your rules). <b>Note:</b> The ":n" notation (e.g.,
|
||
eth0:0) is deprecated and will disappear eventually. Neither
|
||
iproute (ip and tc) nor iptables supports that notation so neither
|
||
does Shorewall. <br>
|
||
<br>
|
||
<b>Example 1:</b><br>
|
||
<br>
|
||
/etc/shorewall/rules
|
||
|
||
<pre wrap=""><span class="moz-txt-citetags"></span> # Accept AUTH but only on address 192.0.2.125<br><span
|
||
class="moz-txt-citetags"></span><br><span class="moz-txt-citetags"></span> ACCEPT net fw:192.0.2.125 tcp auth<br><span
|
||
class="moz-txt-citetags"></span></pre>
|
||
<span class="moz-txt-citetags"></span><b>Example
|
||
2 (NAT):</b><br>
|
||
<br>
|
||
<span class="moz-txt-citetags"></span>/etc/shorewall/nat<br>
|
||
|
||
<pre wrap=""><span class="moz-txt-citetags"></span><span
|
||
class="moz-txt-citetags"></span> 192.0.2.126 eth0 10.1.1.126</pre>
|
||
/etc/shorewall/rules
|
||
|
||
<pre wrap=""><span class="moz-txt-citetags"></span> # Accept HTTP on 192.0.2.126 (a.k.a. 10.1.1.126)<br><span
|
||
class="moz-txt-citetags"></span><br> <span class="moz-txt-citetags"></span>ACCEPT net loc:10.1.1.126 tcp www<span
|
||
class="moz-txt-citetags"></span><br></pre>
|
||
<b>Example 3 (DNAT):<br>
|
||
</b>
|
||
<pre> # Forward SMTP on external address 192.0.2.127 to local system 10.1.1.127<br><br> DNAT net loc:10.1.1.127 tcp smtp - 192.0.2.127<br></pre>
|
||
|
||
<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><EFBFBD><EFBFBD><EFBFBD> /sbin/shorewall version</b></font><br>
|
||
<br>
|
||
<font size="2">Last updated 2/22/2003 - <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>
|
||
<br>
|
||
|
||
</body>
|
||
</html>
|