os/doc
3
0
Fork 0
Code Issues Pull requests Projects Releases Wiki Activity

Start review of firewall chapter.

Browse source 
Many more commits to follow.

Sponsored by: iXsystems
This commit is contained in:
Dru Lavigne 2014-02-13 22:45:31 +00:00
parent 2793bd3ee0
commit 56696223fd
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=43909
1 changed files with 72 additions and 72 deletions

144
en_US.ISO8859-1/books/handbook/firewalls/chapter.xml
View file

@ -41,7 +41,7 @@
</indexterm>
<sect1 xml:id="firewalls-intro">
<title>Introduction</title>
<title>Synopsis</title>
<para>Firewalls make it possible to filter the incoming and
outgoing traffic that flows through a system. A firewall can
@ -77,6 +77,25 @@
</listitem>
</itemizedlist>
<para>&os; has three firewalls built into the base system:
<application>PF</application>, <application>IPFILTER</application>, also known as
<application>IPF</application>, and
<application>IPFW</application>.
&os; also provides two traffic shapers for controlling bandwidth
usage: &man.altq.4; and &man.dummynet.4;.
<application>ALTQ</application> has
traditionally been closely tied with <application>PF</application> and
<application>dummynet</application> with <application>IPFW</application>.
Each
firewall uses rules to control the access of packets to and from
a &os; system, although they go about it in different ways and
each has a different rule syntax.</para>
<para>&os; provides multiple firewalls in order to meet the
different requirements and preferences for a wide variety of
users. Each user should evaluate which firewall best meets
their needs.</para>
<para>After reading this chapter, you will know:</para>
<itemizedlist>
@ -112,6 +131,18 @@
<para>Understand basic &os; and Internet concepts.</para>
</listitem>
</itemizedlist>
<note>
<para>Since all firewalls are based on inspecting the values of
selected packet control fields, the creator of the firewall
ruleset must have an understanding of how
<acronym>TCP/IP</acronym> works, what the different values in
the packet control fields are, and how these values are used in
a normal session conversation. For a good introduction, refer
to
<link xlink:href="http://www.ipprimer.com/overview.cfm">Daryl's
TCP/IP Primer</link>.</para>
</note>
</sect1>
<sect1 xml:id="firewalls-concepts">
@ -156,37 +187,6 @@
combination of stateful and non-stateful behavior.</para>
</sect1>
<sect1 xml:id="firewalls-apps">
<title>Firewall Packages</title>
<para>&os; has three firewalls built into the base system:
<emphasis>IPFILTER</emphasis>, also known as
<acronym>IPF</acronym>, <emphasis>IPFIREWALL</emphasis>, also
known as <acronym>IPFW</acronym>, and <acronym>PF</acronym>).
&os; also provides two traffic shapers for controlling bandwidth
usage: &man.altq.4; and &man.dummynet.4;. Dummynet has
traditionally been closely tied with <acronym>IPFW</acronym>,
and <acronym>ALTQ</acronym> with <acronym>PF</acronym>. Each
firewall uses rules to control the access of packets to and from
a &os; system, although they go about it in different ways and
each has a different rule syntax.</para>
<para>&os; provides multiple firewalls in order to meet the
different requirements and preferences for a wide variety of
users. Each user should evaluate which firewall best meets
their needs.</para>
<para>Since all firewalls are based on inspecting the values of
selected packet control fields, the creator of the firewall
ruleset must have an understanding of how
<acronym>TCP/IP</acronym> works, what the different values in
the packet control fields are, and how these values are used in
a normal session conversation. For a good introduction, refer
to
<link xlink:href="http://www.ipprimer.com/overview.cfm">Daryl's
TCP/IP Primer</link>.</para>
</sect1>
<sect1 xml:id="firewalls-pf">
<info>
<title>PF and <acronym>ALTQ</acronym></title>
@ -209,20 +209,20 @@
</indexterm>
<para>Since &os;&nbsp;5.3, a ported version of OpenBSD's
<acronym>PF</acronym> firewall has been included as an
integrated part of the base system. <acronym>PF</acronym> is a
<application>PF</application> firewall has been included as an
integrated part of the base system. <application>PF</application> is a
complete, full-featured firewall that has optional support for
<acronym>ALTQ</acronym> (Alternate Queuing), which provides
Quality of Service (<acronym>QoS</acronym>).</para>
<para>Since the OpenBSD Project maintains the definitive
reference for <acronym>PF</acronym> in the
reference for <application>PF</application> in the
<link xlink:href="http://www.openbsd.org/faq/pf/">PF FAQ</link>,
this section of the Handbook focuses on <acronym>PF</acronym> as
this section of the Handbook focuses on <application>PF</application> as
it pertains to &os;, while providing some general usage
information.</para>
<para>More information about porting <acronym>PF</acronym> to &os;
<para>More information about porting <application>PF</application> to &os;
can be found at <uri
xlink:href="http://pf4freebsd.love2party.net/">http://pf4freebsd.love2party.net/</uri>.</para>
@ -252,7 +252,7 @@
can be found in
<filename>/usr/share/examples/pf/</filename>.</para>
<para>The <acronym>PF</acronym> module can also be loaded
<para>The <application>PF</application> module can also be loaded
manually from the command line:</para>
<screen>&prompt.root; <userinput>kldload pf.ko</userinput></screen>
@ -286,17 +286,17 @@
<secondary>device pfsync</secondary>
</indexterm>
<para>While it is not necessary to compile <acronym>PF</acronym>
<para>While it is not necessary to compile <application>PF</application>
support into the &os; kernel, some of PF's advanced features
are not included in the loadable module, namely
&man.pfsync.4;, which is a pseudo-device that exposes certain
changes to the state table used by <acronym>PF</acronym>. It
changes to the state table used by <application>PF</application>. It
can be paired with &man.carp.4; to create failover firewalls
using <acronym>PF</acronym>. More information on
using <application>PF</application>. More information on
<acronym>CARP</acronym> can be found in
<link linkend="carp">of the Handbook</link>.</para>
<para>The following <acronym>PF</acronym> kernel options can be
<para>The following <application>PF</application> kernel options can be
found in <filename>/usr/src/sys/conf/NOTES</filename>:</para>
<programlisting>device pf
@ -320,7 +320,7 @@ device pfsync</programlisting>
<title>Available <filename>rc.conf</filename> Options</title>
<para>The following &man.rc.conf.5; statements can be used to
configure <acronym>PF</acronym> and &man.pflog.4; at
configure <application>PF</application> and &man.pflog.4; at
boot:</para>
<programlisting>pf_enable="YES" # Enable PF (load module if required)
@ -340,14 +340,14 @@ pflog_flags="" # additional flags for pflogd startup</programli
<sect2>
<title>Creating Filtering Rules</title>
<para>By default, <acronym>PF</acronym> reads its configuration
<para>By default, <application>PF</application> reads its configuration
rules from <filename>/etc/pf.conf</filename> and modifies,
drops, or passes packets according to the rules or definitions
specified in this file. The &os; installation includes
several sample files located in
<filename>/usr/share/examples/pf/</filename>. Refer to the
<link xlink:href="http://www.openbsd.org/faq/pf/">PF
FAQ</link> for complete coverage of <acronym>PF</acronym>
FAQ</link> for complete coverage of <application>PF</application>
rulesets.</para>
<warning>
@ -356,18 +356,18 @@ pflog_flags="" # additional flags for pflogd startup</programli
keep in mind that different versions of &os; contain
different versions of PF. Currently,
&os;&nbsp;8.<replaceable>X</replaceable> is using the same
version of <acronym>PF</acronym> as OpenBSD&nbsp;4.1.
version of <application>PF</application> as OpenBSD&nbsp;4.1.
&os;&nbsp;9.<replaceable>X</replaceable> and later is using
the same version of <acronym>PF</acronym> as
the same version of <application>PF</application> as
OpenBSD&nbsp;4.5.</para>
</warning>
<para>The &a.pf; is a good place to ask questions about
configuring and running the <acronym>PF</acronym> firewall.
configuring and running the <application>PF</application> firewall.
Do not forget to check the mailing list archives before asking
questions.</para>
<para>To control <acronym>PF</acronym>, use &man.pfctl.8;.
<para>To control <application>PF</application>, use &man.pfctl.8;.
Below are some useful options to this command. Review
&man.pfctl.8; for a description of all available
options:</para>
@ -482,7 +482,7 @@ options ALTQ_NOPCC # Required for SMP build</programlisting>
<sect2 xml:id="pf-tutorial">
<info>
<title><acronym>PF</acronym> Rule Sets and Tools</title>
<title><application>PF</application> Rule Sets and Tools</title>
<authorgroup>
<author>
@ -497,7 +497,7 @@ options ALTQ_NOPCC # Required for SMP build</programlisting>
</info>
<para>This section demonstrates some useful
<acronym>PF</acronym> features and <acronym>PF</acronym>
<application>PF</application> features and <application>PF</application>
related tools in a series of examples. A more thorough
tutorial is available at <link
xlink:href="http://home.nuug.no/~peter/pf/">http://home.nuug.no/~peter/pf/</link>.</para>
@ -546,7 +546,7 @@ pass out all keep state</programlisting>
Six Dumbest Ideas in Computer Security</link>, and
it is well written too.</para></footnote>. This gives
us the opportunity to introduce two of the features which
make <acronym>PF</acronym> such a wonderful tool:
make <application>PF</application> such a wonderful tool:
<firstterm>lists</firstterm> and
<firstterm>macros</firstterm>.</para>
@ -563,7 +563,7 @@ udp_services = "{ domain }"</programlisting>
<para>Now we have demonstrated several things at once - what
macros look like, that macros may be lists, and that
<acronym>PF</acronym> understands rules using port names
<application>PF</application> understands rules using port names
equally well as it does port numbers. The names are the
ones listed in <filename>/etc/services</filename>. This
gives us something to put in our rules, which we edit
@ -574,7 +574,7 @@ pass out proto tcp to any port $tcp_services keep state
pass proto udp to any port $udp_services keep state</programlisting>
<para>At this point some of us will point out that UDP is
stateless, but <acronym>PF</acronym> actually manages to
stateless, but <application>PF</application> actually manages to
maintain state information despite this. Keeping state for
a UDP connection means that for example when you ask a name
server about a domain name, you will be able to receive its
@ -602,7 +602,7 @@ pass proto udp to any port $udp_services keep state</programlisting>
only, but does not load them. This provides an opportunity
to correct any errors. Under any circumstances, the last
valid rule set loaded will be in force until
<acronym>PF</acronym> is disabled or a new rule set is
<application>PF</application> is disabled or a new rule set is
loaded.</para>
<tip>
@ -623,7 +623,7 @@ pass proto udp to any port $udp_services keep state</programlisting>
<para>To most users, a single machine setup will be of limited
interest, and at this point we move on to more realistic or
at least more common setups, concentrating on a machine
which is running <acronym>PF</acronym> and also acts as a
which is running <application>PF</application> and also acts as a
gateway for at least one other machine.</para>
<sect4 xml:id="pftut-gwpitfalls">
@ -851,7 +851,7 @@ pass from { lo0, $localnet } to any keep state</programlisting>
relationships between the rules in a rule set. The rules
are evaluated from top to bottom, in the sequence they are
written in the configuration file. For each packet or
connection evaluated by <acronym>PF</acronym>,
connection evaluated by <application>PF</application>,
<emphasis>the last matching rule</emphasis> in the rule
set is the one which is applied. The
<literal>quick</literal> keyword offers an escape from the
@ -928,7 +928,7 @@ pass from { lo0, $localnet } to any keep state</programlisting>
gateway is amazingly simple, thanks to the
<acronym>FTP</acronym> proxy program (called
&man.ftp-proxy.8;) included in the base system on &os; and
other systems which offer <acronym>PF</acronym>.</para>
other systems which offer <application>PF</application>.</para>
<para>The <acronym>FTP</acronym> protocol being what it is,
the proxy needs to dynamically insert rules in your rule
@ -944,7 +944,7 @@ pass from { lo0, $localnet } to any keep state</programlisting>
<para>Starting the proxy manually by running
<command>/usr/sbin/ftp-proxy</command> allows testing of
the <acronym>PF</acronym> configuration changes we are
the <application>PF</application> configuration changes we are
about to make.</para>
<para>For a basic configuration, only three elements need to
@ -1006,7 +1006,7 @@ rdr-anchor "ftp-proxy/*"</programlisting>
page.</para>
<para>For ways to run an <acronym>FTP</acronym> server
protected by <acronym>PF</acronym> and &man.ftp-proxy.8;,
protected by <application>PF</application> and &man.ftp-proxy.8;,
look into running a separate <command>ftp-proxy</command>
in reverse mode (using <option>-R</option>), on a separate
port with its own redirecting pass rule.</para>
@ -1099,7 +1099,7 @@ pass inet proto icmp from any to $ext_if keep state</programlisting>
<para>Stopping probes at the gateway might be an attractive
option anyway, but let us have a look at a few other
options which will show some of <acronym>PF</acronym>'s
options which will show some of <application>PF</application>'s
flexibility.</para>
</sect4>
@ -1166,7 +1166,7 @@ pass out on $ext_if inet proto udp from any to any port 33433 &gt;&lt; 33626 kee
places from <link
xlink:href="http://marc.theaimsgroup.com/">http://marc.theaimsgroup.com/</link>),
to be a very valuable resource whenever you need OpenBSD
or <acronym>PF</acronym> related information.</para>
or <application>PF</application> related information.</para>
</sect4>
<sect4 xml:id="pftut-pathmtudisc">
@ -1207,7 +1207,7 @@ pass out on $ext_if inet proto udp from any to any port 33433 &gt;&lt; 33626 kee
<programlisting>pass inet proto icmp all icmp-type $icmp_types keep state</programlisting>
<para><acronym>PF</acronym> allows filtering on all
<para><application>PF</application> allows filtering on all
variations of <acronym>ICMP</acronym> types and codes.
For those who want to delve into what to pass (or not) of
<acronym>ICMP</acronym> traffic, the list of possible
@ -1235,7 +1235,7 @@ pass out on $ext_if inet proto udp from any to any port 33433 &gt;&lt; 33626 kee
and rigid. There will after all be some kinds of data which
are relevant to filtering and redirection at a given time,
but do not deserve to be put into a configuration file!
Quite right, and <acronym>PF</acronym> offers mechanisms for
Quite right, and <application>PF</application> offers mechanisms for
handling these situations as well. Tables are one such
feature, mainly useful as lists which can be manipulated
without needing to reload the entire rule set, and where
@ -1323,7 +1323,7 @@ Sep 26 03:12:44 skapet sshd[24703]: Failed password for invalid user admin from
22222 for a repeat performance.</para>
<para>Since OpenBSD 3.7, and soon after in &os; version 6.0,
<acronym>PF</acronym> has offered a slightly more elegant
<application>PF</application> has offered a slightly more elegant
solution. Pass rules can be written so they maintain
certain limits on what connecting hosts can do. For good
measure, violators can be banished to a table of addresses
@ -1488,10 +1488,10 @@ Sep 26 03:12:44 skapet sshd[24703]: Failed password for invalid user admin from
</sect3>
<sect3 xml:id="pftut-tools">
<title>Other <acronym>PF</acronym> Tools</title>
<title>Other <application>PF</application> Tools</title>
<para>Over time, a number of tools have been developed which
interact with <acronym>PF</acronym> in various ways.</para>
interact with <application>PF</application> in various ways.</para>
<sect4 xml:id="pftut-pftop">
<title>The <application>pftop</application> Traffic
@ -1514,11 +1514,11 @@ Sep 26 03:12:44 skapet sshd[24703]: Failed password for invalid user admin from
<para>Not to be confused with the
<application>spamd</application> daemon which comes
bundled with <application>spamassassin</application>, the
<acronym>PF</acronym> companion
<application>PF</application> companion
<application>spamd</application> was designed to run on a
PF gateway to form part of the outer defense against spam.
<application>spamd</application> hooks into the
<acronym>PF</acronym> configuration via a set of
<application>PF</application> configuration via a set of
redirections.</para>
<para>The main point underlying the
@ -1819,7 +1819,7 @@ rdr pass on $ext_if inet proto tcp from !&lt;spamd-white&gt; to \
can be set in the <literal>options</literal> part of the
ruleset, which precedes the redirection and filtering
rules. This option determines which feedback, if any,
<acronym>PF</acronym> will give to hosts which try to
<application>PF</application> will give to hosts which try to
create connections which are subsequently blocked. The
option has two possible values, <literal>drop</literal>,
which drops blocked packets with no feedback, and
@ -1838,7 +1838,7 @@ rdr pass on $ext_if inet proto tcp from !&lt;spamd-white&gt; to \
<sect5 xml:id="pftut-scrub">
<title><literal>scrub</literal></title>
<para>In <acronym>PF</acronym> versions up to OpenBSD 4.5
<para>In <application>PF</application> versions up to OpenBSD 4.5
inclusive, <literal>scrub</literal> is a keyword which
enables network packet normalization, causing fragmented
packets to be assembled and removing ambiguity.
@ -1853,7 +1853,7 @@ rdr pass on $ext_if inet proto tcp from !&lt;spamd-white&gt; to \
<para>Some services, such as NFS, require some specific
fragment handling options. This is extensively
documented in the <acronym>PF</acronym> user guide and
documented in the <application>PF</application> user guide and
man pages provide all the information you could
need.</para>