Tom Eastep 2007 Thomas M. Eastep 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, 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 is a companion product to Shorewall. 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.

While 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 (Restriction relaxed in Shorewall-perl 4.0.1) 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 similar to restart with the exceptios that: The command fails if Shorewall is not running. A directory name cannot be specified in the command. The refresh command does not alter the Netfilter configuration except for the static blacklist. 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-time Run-time Eliminated initdone clear continue maclog initdone Per-chain (including those associated with actions) start started stop stopped tcclear Compile-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 name To 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 part Example: 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>[,...]] $FW[:<address>[,...]] The DEST column may be one of the following: [all:]<address>[,...] [all:]<interface>[:<address>[,...]] This is a permanent change. The old zone-based rules have never worked right and this is a good time to replace them. I've tried to make the new syntax cover the most common cases without requiring change to existing files. In particular, it will handle the tos file released with Shorewall 1.4 and earlier. Shorewall-perl insists that ipset names begin with a letter and be composed of alphanumeric characters and underscores (_). When used in a Shorewall configuration file, the name must be preceded by a plus sign (+) as with the shell-based compiler. Shorewall is now out of the ipset load/reload business. With scripts generated by the Perl-based Compiler, the Netfilter ruleset is never cleared. That means that there is no opportunity for Shorewall to load/reload your ipsets since that cannot be done while there are any current rules using ipsets. So: Your ipsets must be loaded before Shorewall starts. You are free to try to do that with the following code in /etc/shorewall/start: if [ "$COMMAND" = start ]; then ipset -U :all: :all: ipset -F ipset -X ipset -R < /etc/shorewall/ipsets fi The 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. The PKTTYPE option is ignored by Shorewall-perl. Shorewall-perl 4.0.0 requires Address type match. Shorewall-perl versions 4.0.1 and later will use Address type match if it is available; otherwise, they will behave as if PKTTYPE=No had been specified. Shorewall-perl detects dead policy file entries that result when an entry is masked by an earlier more general entry. Example: #SOURCE DEST POLICY LOG LEVEL all all REJECT info loc net ACCEPT

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.

Perl (I use Perl 5.8.8 but other versions should work fine) Perl Cwd Module Perl File::Basename Module Perl File::Temp Module Perl Getopts::Long Module Perl Carp Module

Either tar -jxf shorewall-perl-4.0.x.tar.bz2 cd shorewall-perl-4.0.x ./install.sh or rpm -ivh shorewall-perl-4.0.x.noarch.rpm

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 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. If you only install one compiler, it is suggested that you do not set SHOREWALL_COMPILER. You may also 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 compiler The -C option overrides the setting in shorewall.conf. Example:shorewall restart -C perl When the Shorewall-perl compiler has been selected, the params file is processed twice, the second time using the -a 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.