Shorewall-perlTomEastep2007Thomas M. EastepPermission 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, with no Front-Cover, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
GNU Free Documentation
License.Shorewall-perl - What is it?Shorewall-perl is a companion product to Shorewall. It requires
Shorewall 3.4.2 or later (Shorewall 3.4.4 or later recommended).Shorewall-perl contains a re-implementation of the Shorewall
compiler written in Perl. The advantages of using Shorewall-perl over
Shorewall-shell (the shell-based compiler included in earlier Shorewall
3.x releases) are:The Shorewall-perl compiler is much faster.The script generated by the compiler uses
iptables-restore to instantiate the Netfilter
configuration. So it runs much faster than the script generated by the
Shorewall-shell compiler.The Shorewall-perl compiler does more thorough checking of the
configuration than the Shorewall-shell compiler does.The error messages produced by the compiler are better, more
consistent and always include the file name and line number where the
error was detected.Going forward, the Shorewall-perl compiler will get all
enhancements; the Shorewall-shell compiler will only get those
enhancements that are easy to retrofit.Shorewall-perl - The down sideWhile there are advantages to using Shorewall-perl, there are also
disadvantages:There are a number of incompatibilities between the
Shorewall-perl compiler and the earlier one.The Perl-based compiler requires the following capabilities
in your kernel and iptables.addrtype match (may be relaxed later)multiport match (will not be relaxed)These capabilities are in current distributions.Now that Netfilter has features to deal reasonably with port
lists, I see no reason to duplicate those features in Shorewall.
The Shorewall-shell compiler goes to great pain (in some cases) to
break very long port lists ( > 15 where port ranges in lists
count as two ports) into individual rules. In the new compiler,
I'm avoiding the ugliness required to do that. The new compiler
just generates an error if your list is too long. It will also
produce an error if you insert a port range into a port list and
you don't have extended multiport support.BRIDGING=Yes is not supported. The kernel code necessary to
support this option was removed in Linux kernel 2.6.20. Alternative bridge
support is provided by Shorewall-perl.The BROADCAST column in the interfaces file is essentially
unused; if you enter anything in this column but '-' or 'detect',
you will receive a warning. This will be relaxed if and when the
addrtype match requirement is relaxed.The 'refresh' command is now synonymous with
'restart'.With the shell-based compiler, extension scripts were copied
into the compiled script and executed at run-time. In many cases,
this approach doesn't work with Shorewall Perl because (almost)
the entire ruleset is built by the compiler. As a result,
Shorewall-perl runs many extension scripts at compile-time rather
than at run-time. Because the compiler is written in Perl, your
extension scripts from earlier versions will no longer
work.The following table summarizes when the various extension
scripts are run:Compile-timeRun-timeEliminatedinitdoneclearcontinuemacloginitdonerefreshPer-chain (including those associated with
actions)startstartedstopstoppedtcclearCompile-time extension scripts are executed using the Perl
'eval `cat <file>`' mechanism. Be sure that each script
returns a 'true' value; otherwise, the compiler will assume that
the script failed and will abort the compilation.When a script is invoked, the $chainref scalar variable will hold a
reference to a chain table entry.$chainref->{name}
contains the name of the chain$chainref->{table}
holds the table nameTo add a rule to the chain:add_rule $chainref, <the
rule>Where<the rule> is a scalar
argument holding the rule text. Do not include "-A
<chain name>"Example:add_rule $chainref, '-j ACCEPT';To insert a rule into the chain:insert_rule $chainref,
<rulenum>, <the
rule>The log_rule_limit function works like it does in the shell
compiler with two exceptions:You pass the chain reference rather than the name of the
chain.The commands are 'add' and 'insert' rather than '-A' and
'-I'.There is only a single "pass as-is to iptables" argument
(so you must quote that partExample: log_rule_limit
'info' ,
$chainref ,
$chainref->{name},
'DROP' ,
'', #Limit
'' , #Log tag
'add'
'-p tcp '; Here is an example of an actual initdone script used with
Shorewall 3.4:run_iptables -t mangle -I PREROUTING -p esp -j MARK --set-mark 0x50
run_iptables -t filter -I INPUT -p udp --dport 1701 -m mark --mark 0x50 -j ACCEPT
run_iptables -t filter -I OUTPUT -p udp --sport 1701 -j ACCEPT
Here is the corresponding script used with
Shorewall-perl:use Shorewall::Chains;
insert_rule $mangle_table->{PREROUTING}, 1, "-p esp -j MARK --set-mark 0x50";
insert_rule $filter_table->{INPUT}, 1, "-p udp --dport 1701 -m mark --mark 0x50 -j ACCEPT";
insert_rule $filter_table->{OUTPUT}, 1, "-p udp --sport 1701 -j ACCEPT";
1;The initdone script is unique because the $chainref variable
is not set before the script is called. The above script
illustrates how the $mangle_table, $filter_table, and $nat_table
references can be used to add or insert rules in arbitrary
chains.The /etc/shorewall/tos file now has
zone-independent SOURCE and DEST columns as do all other files
except the rules and policy files.The SOURCE column may be one of the following:[all:]<address>[,...][all:]<interface>[:<address>[,...]]$FW[:<address>[,...]]The DEST column may be one of the following:[all:]<address>[,...][all:]<interface>[:<address>[,...]]This is a permanent change. The old zone-based rules have
never worked right and this is a good time to replace them. I've
tried to make the new syntax cover the most common cases without
requiring change to existing files. In particular, it will handle
the tos file released with Shorewall 1.4 and earlier.Currently, support for ipsets is only lightly tested (any
volunteers?). That will change with future pre-releases but one
thing is certain -- Shorewall is now out of the ipset load/reload
business. With scripts generated by the Perl-based Compiler, the
Netfilter ruleset is never cleared. That means that there is no
opportunity for Shorewall to load/reload your ipsets since that
cannot be done while there are any current rules using
ipsets.So:Your ipsets must be loaded before Shorewall starts. You
are free to try to do that with the following code in
/etc/shorewall/start:if [ "$COMMAND" = start ]; then
ipset -U :all: :all:
ipset -F
ipset -X
ipset -R < /etc/shorewall/ipsets
fiThe file /etc/shorewall/ipsets will
normally be produced using the ipset -S
command.The above will work most of the time but will fail in a
shorewall stop - shorewall
start sequence if you use ipsets in your
routestopped file (see below).Your ipsets may not be reloaded until Shorewall is
stopped or cleared.If you specify ipsets in your routestopped file then
Shorewall must be cleared in order to reload your
ipsets.As a consequence, scripts generated by the Perl-based
compiler will ignore /etc/shorewall/ipsets
and will issue a warning if you set SAVE_IPSETS=Yes in
shorewall.conf.Because the configuration files (with the exception of
/etc/shorewall/params) are now processed by
the Shorewall-perl compiler rather than by the shell, only the
basic forms of Shell expansion ($variable and ${variable}) are
supported. The more exotic forms such as ${variable:=default} are
not supported. Both variables defined in /etc/shorewall/params and
environmental variables (exported by the shell) can be used in
configuration files.USE_ACTIONS=No is not supported. That option is intended to
minimize Shorewall's footprint in embedded applications. As a
consequence, Default Macros are not supported.DELAYBLACKLISTLOAD=Yes is not supported. The entire ruleset
is atomically loaded with one execution of
iptables-restore.MAPOLDACTIONS=Yes is not supported. People should have
converted to using macros by now.The pre Shorewall-3.0 format of the zones file is not
supported; neither is the
/etc/shorewall/ipsec file.BLACKLISTNEWONLY=No is not permitted with FASTACCEPT=Yes.
This combination doesn't work in previous versions of Shorewall so
the Perl-based compiler simply rejects it.Shorewall-perl has a single rule generator that is used for
all rule-oriented files. So it is important that the syntax is
consistent between files.With shorewall-shell, there is a special syntax in the
SOURCE column of /etc/shorewall/masq to designate "all traffic
entering the firewall on this interface except...".Example:#INTERFACE SOURCE ADDRESSES
eth0 eth1!192.168.4.9 ...Shorewall-perl
uses syntax that is consistent with the rest of
Shorewall:#INTERFACE SOURCE ADDRESSES
eth0 eth1:!192.168.4.9 ...The 'allowoutUPnP' built-in action is no longer supported.
In kernel 2.6.14, the Netfilter team have removed support for '-m
owner --owner-cmd' which that action depended on.Shorewall-perl is dependent on Perl (see the next section) which
has a large disk footprint. This makes Shorewall-perl less desirable
in an embedded environment.Shorewall-perl - PrerequisitesIn addition to Shorewall-3.4.2 or later, you need:Perl (I use Perl 5.8.8 but other versions should work
fine)Perl Cwd ModulePerl File::Basename ModulePerl File::Temp ModulePerl Getopts::Long ModulePerl Carp ModuleShorewall-perl - InstallationShorewall-perl is still part of the current development release. Use it at
your own risk.Eithertar -jxf shorewall-perl-4.0.0-Betax.tar.bz2cd shorewall-perl-4.0.0-Betax./install.shorrpm -ivh shorewall-perl-4.0.0-0Betax.noarch.rpmNote that you can also install the current Shorewall 4.0.0 Beta
version of Shorewall. If you do that and still want access to the legacy
shell-based compiler, you must also install the Shorewall-shell
package.Using Shorewall-perlUsing Shorewall-perl under Shorewall 3.4.2 and Shorewall
3.4.3By default, the Shorewall-shell compiler will be used.To use the Shorewall-perl compiler, add this to
shorewall.conf:SHOREWALL_COMPILER=perlIf you add this setting to
/etc/shorewall/shorewall.conf then by default, the
new compiler will be used on the system.Regardless of the setting of SHOREWALL_COMPILER, there is one
change in Shorewall operation that is triggered simply by installing
Shorewall-perl. Your params file will be processed with the shell's '-a'
option which causes any variables that you set or create in that file to
be automatically exported. Since the params file is processed before
shorewall.conf, using -a insures that the settings
of your params variables are available to the new compiler should it's
use be specified in shorewall.conf.Using Shorewall-perl under Shorewall 3.4.4/4.0.0 Beta and
later.If you only install one compiler, then that compiler will be
used.If you install both compilers, then the compiler actually used
depends on the SHOREWALL_COMPILER setting in
shorewall.conf.The value of this new option can be either 'perl' or
'shell'.If you add 'SHOREWALL_COMPILER=perl' to
/etc/shorewall/shorewall.conf then by default, the
new compiler will be used on the system. If you add it to
shorewall.conf in a separate directory (such as a
Shorewall-lite export directory) then the new compiler will only be used
when you compile from that directory (4.0.0 Beta6 and later
only).If you only install one compiler, it is suggested that you do not
set SHOREWALL_COMPILER.If you install Shorewall-perl under Shorewall 3.4.4 or later, you
can select the compiler to use on the command line using the 'C
option:'-C shell' means use the shell compiler'-C perl' means use the perl compilerThe -C option overrides the setting in
shorewall.conf.Example:shorewall restart -C perlWhen the Shorewall-perl compiler has been selected, the
params file is processed using the
option which causes all variables set within the
file to be exported automatically by the shell. The Shorewall-perl
compiler uses the current environmental variables to perform variable
expansion within the other Shorewall configuration files.