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Jeremy Sowden c93817f30b Correct GFDL text embedded in document sources 
The invariant sections clause doesn't quite match the official text.  It should
read:

  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts

not:

  with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
2023-01-31 22:50:37 +00:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article id="usefull_links">
<!--$Id$-->
<articleinfo>
<title>Shorewall Troubleshooting Guide</title>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2001-2007, 2014</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<legalnotice>
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version
1.2 or any later version published by the Free Software Foundation; with
no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled
<quote><ulink type="" url="GnuCopyright.htm">GNU Free Documentation
License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<section id="Start">
<title><quote>shorewall start</quote> and <quote>shorewall restart</quote>
Errors</title>
<para>If the error is detected by the Shorewall compiler, it should be
fairly obvious where the problem was found. Each error message includes
the configuration file name and line number where the error was detected
and often gives the particular item in error. The item is either enclosed
in parentheses or is at the end following a colon (":").</para>
<para>Example:<programlisting>gateway:~/test # shorewall restart .
Compiling...
ERROR: Invalid ICMP Type (0/400) : /root/test/rules (line 19)
gateway:~/test # </programlisting>In this case, line 19 in the rules file
specified an invalid ICMP Type (0/400).</para>
<para>Additional information about the error can be obtained using the
'debug' keyword (Shorewall 4.4.19 and earlier) or using the (-T)
option.</para>
<para>Example (4.4.19 and earlier):</para>
<para><programlisting>gateway:~/test # shorewall debug restart
Compiling...
ERROR: Invalid ICMP Type (0/400) : /root/test/rules (line 19) at /usr/share/shorewall/Shorewall/Config.pm line 338
Shorewall::Config::fatal_error('Invalid ICMP Type (0/400)') called at /usr/share/shorewall/Shorewall/Chains.pm line 885
Shorewall::Chains::validate_icmp('0/400') called at /usr/share/shorewall/Shorewall/Chains.pm line 949
Shorewall::Chains::do_proto('icmp', '0/400', '-') called at /usr/share/shorewall/Shorewall/Rules.pm line 1055
Shorewall::Rules::process_rule1('ACCEPT', 'loc', 'net', 'icmp', '0/400', '-', '-', '-', '-', ...) called at /usr/share/shorewall/Shorewall/Rules.pm line 1290
Shorewall::Rules::process_rule('ACCEPT', 'loc', 'net', 'icmp', '0/400', '-', '-', '-', '-', ...) called at /usr/share/shorewall/Shorewall/Rules.pm line 1336
Shorewall::Rules::process_rules() called at /usr/share/shorewall/Shorewall/Compiler.pm line 799
Shorewall::Compiler::compiler('/var/lib/shorewall/.restart', '/root/test', 0, 4) called at /usr/share/shorewall/compiler.pl line 86
gateway:~/test # </programlisting></para>
<para>Example (4.4.20 and later):</para>
<programlisting>gateway:~/test # shorewall restart -T
Compiling...
ERROR: Invalid ICMP Type (0/400) : /root/test/rules (line 19) at /usr/share/shorewall/Shorewall/Config.pm line 338
Shorewall::Config::fatal_error('Invalid ICMP Type (0/400)') called at /usr/share/shorewall/Shorewall/Chains.pm line 885
Shorewall::Chains::validate_icmp('0/400') called at /usr/share/shorewall/Shorewall/Chains.pm line 949
Shorewall::Chains::do_proto('icmp', '0/400', '-') called at /usr/share/shorewall/Shorewall/Rules.pm line 1055
Shorewall::Rules::process_rule1('ACCEPT', 'loc', 'net', 'icmp', '0/400', '-', '-', '-', '-', ...) called at /usr/share/shorewall/Shorewall/Rules.pm line 1290
Shorewall::Rules::process_rule('ACCEPT', 'loc', 'net', 'icmp', '0/400', '-', '-', '-', '-', ...) called at /usr/share/shorewall/Shorewall/Rules.pm line 1336
Shorewall::Rules::process_rules() called at /usr/share/shorewall/Shorewall/Compiler.pm line 799
Shorewall::Compiler::compiler('/var/lib/shorewall/.restart', '/root/test', 0, 4) called at /usr/share/shorewall/compiler.pl line 86
gateway:~/test # </programlisting>
<para>This information is useful to Shorewall support if you need to
<ulink url="support.html">file a problem report</ulink>.</para>
<para>The end of the compile phase is signaled by a message such as the
following:<programlisting>Shorewall configuration compiled to /var/lib/shorewall/.restart</programlisting>Errors
occurring past that point are said to occur at
<firstterm>run-time</firstterm> because they occur during the running of
the compiled firewall script (/var/lib/shorewall/.restart in the case of
the above message).</para>
<para>One common run-time failure is that the iptables-restore program
encounters an error. This will produce an error such as the
following:<programlisting>...
Restarting Shorewall....
iptables-restore v1.3.6: No chain/target/match by that name
Error occurred at line: 83
Try `iptables-restore -h' or 'iptables-restore --help' for more information.
ERROR: iptables-restore Failed. Input is in /var/lib/shorewall/.iptables-restore-input
Restoring Shorewall...
Shorewall restored from /var/lib/shorewall/restore
Terminated
gateway:~/test # </programlisting>A look at /var/lib/shorewall/restore at line
83 might show something like the following:<programlisting>-A reject -p tcp -j REJECT --reject-with tcp-reset</programlisting>In
this case, the user had compiled his own kernel and had forgotten to
include REJECT target support (see <ulink
url="kernel.htm">kernel.htm</ulink>).</para>
<para>You may also include the word <emphasis role="bold">debug</emphasis>
as the first argument to the <filename>/sbin/shorewall</filename> and
<filename>/sbin/shorewall-lite</filename> commands.<programlisting><command>shorewall debug restart</command></programlisting>In
most cases, <emphasis role="bold">debug</emphasis> is a synonym for
<emphasis role="bold">trace</emphasis>. The exceptions are:</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">debug</emphasis> is ignored by the
Shorewall compiler.</para>
</listitem>
<listitem>
<para><emphasis role="bold">debug</emphasis> causes altered behavior
of generated scripts. These scripts normally use<command>
iptables-restore</command> to install the Netfilter ruleset but with
<emphasis role="bold">debug</emphasis>, the commands normally passed
to <command>iptables-restore</command> in its input file are passed
individually to <command>iptables</command>. This is a diagnostic aid
which allows identifying the individual command that is causing
<command>iptables-restore</command> to fail; it should be used when
iptables-restore fails when executing a <command>COMMIT</command>
command.</para>
</listitem>
</itemizedlist>
<warning>
<para>The <emphasis role="bold">debug</emphasis> feature is strictly for
problem analysis. When <emphasis role="bold">debug</emphasis> is
used:</para>
<orderedlist>
<listitem>
<para>The firewall is made 'wide open' before the rules are
applied.</para>
</listitem>
<listitem>
<para>The <filename>stoppedrules (routestopped)</filename> file is
not consulted.</para>
</listitem>
<listitem>
<para>The rules are applied in the canonical
<command>iptables-restore</command> order. So if you need critical
hosts to be always available during start/restart, you may not be
able to use <emphasis role="bold">debug</emphasis>.</para>
</listitem>
</orderedlist>
</warning>
<para>In other run-time failure cases:<itemizedlist>
<listitem>
<para>Make a note of the error message that you see.</para>
</listitem>
<listitem>
<para><command>shorewall debug start 2&gt;
/tmp/trace</command></para>
</listitem>
<listitem>
<para>Look at the <filename>/tmp/trace</filename> file and see if
that helps you determine what the problem is. Be sure you find the
place in the log where the error message you saw is generated -- you
should find the message near the end of the log.</para>
</listitem>
<listitem>
<para>If you still can't determine what's wrong then see the <ulink
url="support.htm">support page</ulink>.</para>
</listitem>
</itemizedlist></para>
</section>
<section id="Network">
<title>Your Network Environment</title>
<para>Many times when people have problems with Shorewall, the problem is
actually an ill-conceived network setup. Here are several popular
snafus:</para>
<itemizedlist>
<listitem>
<para>Port Forwarding where client and server are in the same subnet.
See <ulink url="FAQ.htm#faq2">FAQ 2</ulink>.</para>
</listitem>
<listitem>
<para>Trying to test net-&gt;loc DNAT rules from inside your firewall.
You must test these rules from <emphasis
role="bold">outside</emphasis> your firewall.</para>
</listitem>
<listitem>
<para>Multiple interfaces connected to the same HUB or Switch. Given
the way that the Linux kernel respond to ARP <quote>who-has</quote>
requests, this type of setup <emphasis role="bold">does NOT work the
way that you expect it to</emphasis>. You can test using this kind of
configuration if you specify the <emphasis
role="bold">arp_filter</emphasis> option or the <emphasis
role="bold">arp_ignore</emphasis> option in <filename><ulink
url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink></filename>
for all interfaces connected to the common hub/switch. <emphasis
role="bold">Using such a setup with a production firewall is strongly
recommended against</emphasis>.</para>
</listitem>
</itemizedlist>
</section>
<section id="NewDevice">
<title>New Device Doesn't Work?</title>
<para>If you have just added a new device such as VOIP and it doesn't
work, be sure that you have assigned it an IP address in your local
network and that its default gateway has been set to the IP address of
your internal interface. For many of these devices, the simplest solution
is to run a DHCP server; running it on your firewall is fine — be sure to
set the <emphasis role="bold">dhcp</emphasis> option on your internal
interface in <ulink
url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink>.</para>
</section>
<section id="Connections">
<title>Connection Problems</title>
<para>One very important thing to remember is that not all connection
problems are Shorewall configuration problems. If the connection that is
giving you problems is to or from the firewall system or if it doesn't
rely on NAT or Proxy ARP then you can often eliminate Shorewall using a
simple test:</para>
<itemizedlist>
<listitem>
<para><command>/sbin/shorewall clear</command></para>
</listitem>
<listitem>
<para>Try the connection. If it works then the problem is in your
Shorewall configuration; if the connection still doesn't work then the
problem is not with Shorewall or the way that it is configured.</para>
</listitem>
<listitem>
<para>Be sure to <command>/sbin/shorewall start</command> after the
test.</para>
</listitem>
</itemizedlist>
<para>If you still suspect Shorewall and the appropriate policy for the
connection that you are trying to make is ACCEPT, please DO NOT ADD
ADDITIONAL ACCEPT RULES TRYING TO MAKE IT WORK. Such additional rules will
NEVER make it work, they add clutter to your rule set and they represent a
big security hole in the event that you forget to remove them
later.</para>
<para>I also recommend against setting all of your policies to ACCEPT in
an effort to make something work. That robs you of one of your best
diagnostic tools - the <quote>Shorewall</quote> messages that Netfilter
will generate when you try to connect in a way that isn't permitted by
your rule set.</para>
<para>Check your log (<quote><command>/sbin/shorewall show
log</command></quote>). If you don't see Shorewall messages, then your
problem is probably NOT a Shorewall problem. If you DO see packet
messages, it may be an indication that you are missing one or more rules
-- see <ulink url="FAQ.htm#faq17">FAQ 17</ulink>.</para>
<para>While you are troubleshooting, it is a good idea to clear LOGLIMIT
in
<filename><filename>/etc/shorewall/shorewall.conf</filename></filename>:</para>
<para><programlisting>LOGLIMIT=</programlisting>This way, you will see all
of the log messages being generated (be sure to restart shorewall after
clearing thIs variable).</para>
<example id="Example2">
<title>Log Message</title>
<programlisting>Jun 27 15:37:56 gateway kernel: Shorewall:all2all:REJECT:IN=eth2
OUT=eth1 SRC=192.168.2.2
DST=192.168.1.3 LEN=67 TOS=0x00
PREC=0x00 TTL=63 ID=5805 DF
PROTO=UDP SPT=1803 DPT=53 LEN=47</programlisting>
<para>Let's look at the important parts of this message:</para>
<itemizedlist>
<listitem>
<para>all2all:REJECT - This packet was REJECTed out of the all2all
chain -- the packet was rejected under the
<quote>all</quote>-&gt;<quote>all</quote> REJECT policy (see <ulink
url="FAQ.htm#faq17">FAQ 17</ulink>).</para>
</listitem>
<listitem>
<para>IN=eth2 - the packet entered the firewall via eth2</para>
</listitem>
<listitem>
<para>OUT=eth1 - if accepted, the packet would be sent on
eth1</para>
</listitem>
<listitem>
<para>SRC=192.168.2.2 - the packet was sent by 192.168.2.2</para>
</listitem>
<listitem>
<para>DST=192.168.1.3 - the packet is destined for
192.168.1.3</para>
</listitem>
<listitem>
<para>PROTO=UDP - UDP Protocol</para>
</listitem>
<listitem>
<para>DPT=53 - DNS</para>
</listitem>
</itemizedlist>
<para>In this case, 192.168.2.2 was in the <quote>dmz</quote> zone and
192.168.1.3 is in the <quote>loc</quote> zone. I was missing the
rule:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST
# PORT(S)
ACCEPT dmz loc udp 53</programlisting>
</example>
</section>
<section id="Ping">
<title>Ping Problems</title>
<para>Either can't ping when you think you should be able to or are able
to ping when you think that you shouldn't be allowed? Shorewall's
<quote>Ping</quote> Management is <ulink url="ping.html">described
here</ulink>. Here are a couple of tips:</para>
<itemizedlist>
<listitem>
<para>Remember that Shorewall doesn't automatically allow ICMP type 8
(<quote>ping</quote>) requests to be sent between zones. If you want
pings to be allowed between zones, you need a rule of the form:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST
# PORT(S)
Ping(ACCEPT)<emphasis>&lt;source zone&gt;</emphasis> <emphasis>&lt;destination zone&gt;</emphasis></programlisting>
<para>The ramifications of this can be subtle. For example, if you
have the following in <filename><ulink
url="NAT.htm">/etc/shorewall/nat</ulink></filename>:</para>
<programlisting>#EXTERNAL INTERFACE INTERNAL
10.1.1.2 eth0 130.252.100.18</programlisting>
<para>and you ping 130.252.100.18, unless you have allowed icmp type 8
between the zone containing the system you are pinging from and the
zone containing 10.1.1.2, the ping requests will be dropped.</para>
</listitem>
<listitem>
<para>Ping requests are subject to logging under your policies. So
ping floods can cause an equally big flood of log messages. To
eliminate these, as the last rule in your /etc/shorewall/rules file
add:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST
# PORT(S)
Ping(DROP)net all</programlisting>
</listitem>
</itemizedlist>
</section>
<section id="Other">
<title>Some Things to Keep in Mind</title>
<itemizedlist>
<listitem>
<para><emphasis role="bold">You cannot test your firewall from the
inside</emphasis>. Just because you send requests to your firewall
external IP address does not mean that the request will be associated
with the external interface or the <quote>net</quote> zone. Any
traffic that you generate from the local network will be associated
with your local interface and will be treated as loc-&gt;fw
traffic.</para>
</listitem>
<listitem>
<para><emphasis role="bold">IP addresses are properties of systems,
not of interfaces</emphasis>. It is a mistake to believe that your
firewall is able to forward packets just because you can ping the IP
address of all of the firewall's interfaces from the local network.
The only conclusion you can draw from such pinging success is that the
link between the local system and the firewall works and that you
probably have the local system's default gateway set correctly.</para>
</listitem>
<listitem>
<para><emphasis role="bold">All IP addresses configured on firewall
interfaces are in the $FW (fw) zone</emphasis>. If 192.168.1.254 is
the IP address of your internal interface then you can write
<quote><emphasis role="bold">$FW:192.168.1.254</emphasis></quote> in a
rule but you may not write <quote><emphasis
role="bold">loc:192.168.1.254</emphasis></quote>. Similarly, it is
nonsensical to add 192.168.1.254 to the <emphasis
role="bold">loc</emphasis> zone using an entry in
<filename>/etc/shorewall/hosts</filename>.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Reply packets do NOT automatically follow
the reverse path of the one taken by the original request</emphasis>.
All packets are routed according to the routing table of the host at
each step of the way. This issue commonly comes up when people install
a Shorewall firewall parallel to an existing gateway and try to use
DNAT through Shorewall without changing the default gateway of the
system receiving the forwarded requests. Requests come in through the
Shorewall firewall where the destination IP address gets rewritten but
replies go out unmodified through the old gateway.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Shorewall itself has no notion of inside
or outside</emphasis>. These concepts are embodied in how Shorewall is
configured.</para>
</listitem>
</itemizedlist>
</section>
<section id="More">
<title>Other Gotchas</title>
<itemizedlist>
<listitem>
<para>Seeing rejected/dropped packets logged out of the INPUT or
FORWARD chains? This means that:</para>
<orderedlist>
<listitem>
<para>your zone definitions are screwed up and the host that is
sending the packets or the destination host isn't in any zone
(using an <ulink
url="manpages/shorewall-hosts.html"><filename>/etc/shorewall/hosts</filename></ulink>
file are you?); or</para>
</listitem>
<listitem>
<para>the source and destination hosts are both connected to the
same interface and you don't have a policy or rule for the source
zone to or from the destination zone or you haven't set the
<emphasis role="bold">routeback</emphasis> option for the
interface in <ulink
url="manpages/shorewall-interfaces.html"><filename>/etc/shorewall/interfaces</filename></ulink>.</para>
</listitem>
<listitem>
<para>You have connected two firewall interfaces (from different
zones) to the same hub or switch.</para>
</listitem>
</orderedlist>
</listitem>
<listitem>
<para>If you specify <quote>routefilter</quote> for an interface, that
interface must be up prior to starting the firewall.</para>
</listitem>
<listitem>
<para>Is your routing correct? For example, internal systems usually
need to be configured with their default gateway set to the IP address
of their nearest firewall interface. One often overlooked aspect of
routing is that in order for two hosts to communicate, the routing
between them must be set up <emphasis role="bold">in both
directions</emphasis>. So when setting up routing between <emphasis
role="bold">A</emphasis> and <emphasis role="bold">B</emphasis>, be
sure to verify that the route from <emphasis role="bold">B</emphasis>
back to <emphasis role="bold">A</emphasis> is defined and
correct.</para>
</listitem>
<listitem>
<para>Do you have your kernel properly configured? <ulink
url="kernel.htm">Click here to see kernel configuration
information</ulink>.</para>
</listitem>
</itemizedlist>
</section>
<section id="Support">
<title>Still Having Problems?</title>
<para>See the <ulink url="support.htm">Shorewall Support
Page</ulink>.</para>
</section>
</article>
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