Beginning with Shorewall version 3.4, man pages are provided in section 5 for each of the Shorewall configuration files. The name of the page is formed by prefixing the file name with "shorewall-".

Example — To view the manual page for /etc/shorewall/interfaces:

man shorewall-interfaces

The /etc/shorewall/shorewall.conf file is an exception -- the man page for that file is 'shorewall.conf':

man shorewall.conf

You may place comments in configuration files by making the first non-whitespace character a pound sign (“#”). You may also place comments at the end of any line, again by delimiting the comment from the rest of the line with a pound sign.

# This is a comment
ACCEPT  net     $FW      tcp     www     #This is an end-of-line comment

Beginning with Shorewall version 3.3.3, if you kernel and iptables contain comment match support (see the output of shorewall show capabilities), then you can attach comments to Netfilter rules. This feature is available in the following files:

To attach a comment to one or more rules, insert a record above the rules that begins with the word COMMENT (must be in all caps). The remainder of the line is treated as a comment -- that comment will appear delimited by "/* ... */" in the output of the shorewall[-lite] show and shorewall[-lite] dump commands. The comment will be attached to each generated rule until another COMMENT line appears. To stop attaching comments to rules, simply insert a line that contains the single word COMMENT.

Example (/etc/shorewall/rules):

COMMENT Stop NETBIOS noise

REJECT          loc                             net                     tcp     137,445
REJECT          loc                             net                     udp     137:139

COMMENT Stop my idiotic work laptop from sending to the net with an HP source/dest IP address

DROP            loc:!192.168.0.0/22             net

COMMENT

Here's the corresponding output from /sbin/shorewall-lite:

gateway:~ # shorewall-lite show loc2net
Shorewall Lite 3.3.3 Chains loc2net at gateway - Mon Oct 16 15:04:52 PDT 2006

Counters reset Mon Oct 16 14:52:17 PDT 2006

Chain loc2net (1 references)
 pkts bytes target     prot opt in     out     source               destination
    0     0 LOG        tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:25 LOG flags 0 level 6 prefix `FW:loc2net:REJECT:'
    0     0 reject     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:25
    0     0 LOG        udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpts:1025:1031 LOG flags 0 level 6 prefix `FW:loc2net:REJECT:'
    0     0 reject     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpts:1025:1031
    0     0 reject     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           multiport dports 137,445 /* Stop NETBIOS noise */
    0     0 reject     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpts:137:139 /* Stop NETBIOS noise */
    0     0 DROP       all  --  *      *      !192.168.0.0/22       0.0.0.0/0           /* Stop my idiotic work laptop from sending to the net with an HP source/dest IP address */
    5   316 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0
gateway:~ #

COMMENT lines in macro files work somewhat differently from other files. COMMENT lines in macros are ignored if COMMENT support is not available or if there was a COMMENT in use when the top-level macro was invoked. This allows the following:

/usr/share/shorewall/macro.SSH:

#ACTION SOURCE DEST  PROTO DEST    SOURCE  RATE  USER/
#                          PORT(S) PORT(S) LIMIT GROUP
COMMENT SSH
PARAM   -      -     tcp   22 

/etc/shorewall/rules:

COMMENT Allow SSH from home
SSH/ALLOW    net:$MYIP      $FW
COMMENT

The comment line in macro.SSH will not override the COMMENT line in the rules file and the generated rule will show /* Allow SSH from home */ when displayed through the Shorewall show and dump commands.

If you don't want to supply a value in a column but want to supply a value in a following column, simply enter '-' to make the column appear empty.

Example:

#INTERFACE         BROADCAST            OPTIONS
br0                -                    routeback

You may continue lines in the configuration files using the usual backslash (“\”) followed immediately by a new line character (Enter key).

ACCEPT  net     $FW      tcp \↵
smtp,www,pop3,imap  #Services running on the firewall

Any configuration file may contain INCLUDE directives. An INCLUDE directive consists of the word INCLUDE followed by a path name and causes the contents of the named file to be logically included into the file containing the INCLUDE. Relative path names given in an INCLUDE directive are resolved using the current CONFIG_PATH setting (see shorewall.conf(5)).

INCLUDE's may be nested to a level of 3 -- further nested INCLUDE directives are ignored with a warning message.

     shorewall/params.mgmt:
 
        MGMT_SERVERS=1.1.1.1,2.2.2.2,3.3.3.3
         TIME_SERVERS=4.4.4.4
         BACKUP_SERVERS=5.5.5.5
 
        ----- end params.mgmt -----
 
     shorewall/params:
 
        # Shorewall 1.3 /etc/shorewall/params
         [..]
         #######################################
  
         INCLUDE params.mgmt    
   
       # params unique to this host here
       #LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE
 
       ----- end params -----
 
     shorewall/rules.mgmt:
 
       ACCEPT net:$MGMT_SERVERS   $FW                  tcp    22
       ACCEPT $FW                 net:$TIME_SERVERS    udp    123
       ACCEPT $FW                 net:$BACKUP_SERVERS  tcp    22
 
      ----- end rules.mgmt -----
 
     shorewall/rules:
 
      # Shorewall version 1.3 - Rules File
       [..]
       #######################################
  
       INCLUDE rules.mgmt     
   
       # rules unique to this host here
       #LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE
 
     ----- end rules -----

gateway:/etc/shorewall # ls rules.d
ALL.rules  DNAT.rules  FW.rules  NET.rules  REDIRECT.rules  VPN.rules
gateway:/etc/shorewall # 

SECTION NEW
SHELL cat /etc/shorewall/rules.d/*.rules

You may use the /etc/shorewall/params file to set shell variables that you can then use in some of the other configuration files.

It is suggested that variable names begin with an upper case letter to distinguish them from variables used internally within the Shorewall programs

Example:

Variables may be used anywhere in the other configuration files.

/etc/shorewall/zones:

        #ZONE        TYPE          OPTIONS
        fw           firewall

/etc/shorewall/params:

        FW=fw
        BLARG=$FW:206.124.146.176

Because the /etc/shorewall/params file is simply sourced into the shell, you can place arbitrary shell code in the file and it will be executed each time that the file is read. Any code included should follow these guidelines:

When expanding a variable, the acceptable forms of expansion depend on whether you are using Shorewall-shell or Shorewall-perl.

This feature was added in Shorewall-perl 4.0.6. To use it, you must be running 4.0.6 or later and must be using Shorewall-perl (SHOREWALL_COMPILER=perl in shorewall.conf).

Earlier versions of Shorewall offered extension scripts to allow users to extend Shorewall's functionality. Extension scripts were designed to work under the limitations of the Bourne Shell. With Shorewall-perl, Embedded scripts offer a richer and more flexible extension capability.

While inline scripts scripts may be written in either Shell or Perl, those written in Perl have a lot more power.

Embedded scripts can be either single-line or multi-line. Single line scripts take one of the following forms:

Shell scripts run in a child shell process and their output is piped back to the compiler which processes that output as if it were embedded at the point of the script.

Example: The following entries in /etc/shorewall/rules are equivalent:

SHELL for z in net loc dmz; do echo "ACCEPT $z fw tcp 22"; done

ACCEPT net fw tcp 22
ACCEPT loc fw tcp 22
ACCEPT dmz fw tcp 22

Perl scripts run in the context of of the compiler process. To produce output that will be processed by the compiler as if it were embedded in the file at the point of the script, pass that output to the shorewall() function. The Perl equivalent of the above SHELL script would be:

PERL for ( qw/net loc dmz/ ) { shorewall "ACCEPT $_ fw tcp 22"; }

Perl scripts are implicitly prefixed by the following:

package Shorewall::User;
use Shorewall::Config qw/shorewall/;

As part of the change that added embedded scripts:

Multi-line scripts use one of the following forms:

BEGIN SHELL
<shell script>
END [ SHELL ]

BEGIN PERL [;]
<perl script>
END [ PERL ] [;]

Note: The '[' and ']' above are meta-characters which indicate that what they enclose is optional and may be omitted. So you may follow PERL with a semicolon ( ':') or you may omit the semicolon.

Host addresses in Shorewall configuration files may be specified as either IP addresses or DNS Names.

DNS names in iptables rules aren't nearly as useful as they first appear. When a DNS name appears in a rule, the iptables utility resolves the name to one or more IP addresses and inserts those addresses into the rule. So changes in the DNS->IP address relationship that occur after the firewall has started have absolutely no effect on the firewall's rule set.

For some sites, using DNS names is very risky. Here's an example:

teastep@ursa:~$ dig pop.gmail.com

; <<>> DiG 9.4.2-P1 <<>> pop.gmail.com
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1774
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 7, ADDITIONAL: 0

;; QUESTION SECTION:
;pop.gmail.com.               IN A

;; ANSWER SECTION:
pop.gmail.com.          300   IN CNAME gmail-pop.l.google.com.
gmail-pop.l.google.com. 300   IN A     209.85.201.109
gmail-pop.l.google.com. 300   IN A     209.85.201.111

Note that the TTL is 300 -- 300 seconds is only 5 minutes. So five minutes later, the answer may change!

So this rule may work for five minutes then suddently stop working:

#ACTION        SOURCE               DEST              PROTO             DEST
#                                                                       PORT(S)
POP/ACCEPT     loc                  net:pop.gmail.com

If your firewall rules include DNS names then:

Each DNS name must be fully qualified and include a minimum of two periods (although one may be trailing). This restriction is imposed by Shorewall to insure backward compatibility with existing configuration files.

DNS names may not be used as:

These restrictions are imposed by Netfilter and not by Shorewall.

Comma-separated lists are allowed in a number of contexts within the configuration files. A comma separated list:

Where specifying an IP address, a subnet or an interface, you can precede the item with “!” to specify the complement of the item. For example, !192.168.1.4 means “any host but 192.168.1.4”. There must be no white space following the “!”.

Shorewall 3.0 differs from earlier versions in that in most contexts where a comma-separated list of addresses is accepted, an exclusion list may also be included. An exclusion list is a comma-separated list of addresses that begins with "!".

Example:

!192.168.1.3,192.168.1.12,192.168.1.32/27

The above list refers to "All addresses except 192.168.1.3, 192.168.1.12 and 192.168.1.32-192.168.1.63.

Exclusion lists can also be added after a network address.

Example:

192.168.1.0/24!192.168.1.3,192.168.1.12,192.168.1.32/27

The above list refers to "All addresses in 192.168.1.0-192.168.1.255 except 192.168.1.3, 192.168.1.12 and 192.168.1.32-192.168.1.63.

If you kernel and iptables have iprange match support, you may use IP address ranges in Shorewall configuration file entries; IP address ranges have the syntax <low IP address>-<high IP address>. Example: 192.168.1.5-192.168.1.12.

To see if your kernel and iptables have the required support, use the shorewall show capabilities command:

>~ shorewall show capabilities
... 
Shorewall has detected the following iptables/netfilter capabilities:
   NAT: Available
   Packet Mangling: Available
   Multi-port Match: Available
   Connection Tracking Match: Available
   Packet Type Match: Not available
   Policy Match: Available
   Physdev Match: Available
   IP range Match: Available <-------------- 

Unless otherwise specified, when giving a protocol number you can use either an integer or a protocol name from /etc/protocols. Similarly, when giving a port number you can use either an integer or a service name from /etc/services.

cp /usr/share/shorewall-perl/Shorewall/Ports.pm /usr/share/shorewall-perl/Shorewall/Ports.pm.backup
/usr/share/shorewall/buildports.pm > /usr/share/shorewall-perl/Shorewall/Ports.pm

Also, unless otherwise documented, a protocol number/name can be preceded by '!' to specify "All protocols except this one" (e.g., "!tcp"). Shorewall-perl support for that feature was added in Shorewall 4.2.6.

If you need to specify a range of ports, the proper syntax is <low port number>:<high port number>. For example, if you want to forward the range of tcp ports 4000 through 4100 to local host 192.168.1.3, the entry in /etc/shorewall/rules is:

#ACTION    SOURCE     DESTINATION     PROTO     DEST PORTS(S)
DNAT       net        loc:192.168.1.3 tcp       4000:4100

If you omit the low port number, a value of zero is assumed; if you omit the high port number, a value of 65535 is assumed.

Also, unless otherwise documented, a port range can be preceded by '!' to specify "All ports except those in this range" (e.g., "!4000:4100"). Shorewall-perl support for that feature was added in Shorewall 4.2.6.

In most cases where a port or port range may appear, a comma-separated list of ports or port ranges may also be entered. Shorewall will use the Netfilter multiport match capability if it is available (see the output of "shorewall show capabilities") and if its use is appropriate.

Shorewall can use multiport match if:

Also, unless otherwise documented, a port list can be preceded by '!' to specify "All ports except these" (e.g., "!80,443"). Shorewall-perl support for that feature was added in Shorewall 4.2.6.

Media Access Control (MAC) addresses can be used to specify packet source in several of the configuration files. In order to control traffic to/from a host by its MAC address, the host must be on the same network as the firewall.

To use this feature, your kernel must have MAC Address Match support (CONFIG_IP_NF_MATCH_MAC) included.

MAC addresses are 48 bits wide and each Ethernet Controller has a unique MAC address.

In GNU/Linux, MAC addresses are usually written as a series of 6 hex numbers separated by colons.

     gateway:~ # ip link ls dev eth0
     4: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc htb qlen 1000
         link/ether 02:00:08:E3:FA:55 brd ff:ff:ff:ff:ff:ff
     gateway:~ #

Because Shorewall uses colons as a separator for address fields, Shorewall requires MAC addresses to be written in another way. In Shorewall, MAC addresses begin with a tilde (“~”) and consist of 6 hex numbers separated by hyphens. In Shorewall, the MAC address in the example above would be written ~02-00-08-E3-FA-55.

Shorewall allows you to have configuration directories other than /etc/shorewall. The shorewall check, start and restart commands allow you to specify an alternate configuration directory and Shorewall will use the files in the alternate directory rather than the corresponding files in /etc/shorewall. The alternate directory need not contain a complete configuration; those files not in the alternate directory will be read from /etc/shorewall.

This facility permits you to easily create a test or temporary configuration by

Shorewall allows you to save the currently-running configuration in a form that permits it to be re-installed quickly. When you save the configuration using the shorewall save command, the running configuration is saved in a file in the /var/lib/shorewall directory. The default name of that file is /var/lib/shorewall/restore but you can specify a different name as part of the command. For example, the command shorewall save standard will save the running configuration in /var/lib/shorewall/standard. A saved configuration is re-installed using the shorewall restore command. Again, that command normally will restore the configuration saved in /var/lib/shorewall/restore but as with the save command, you can specify a different file name in the command. For example, shorewall restore standard will re-install the configuration saved in /var/lib/shorewall/standard. By permitting you to save different configurations under different names, Shorewall provides a means for quickly switching between these different saved configurations.

As mentioned above, the default configuration is called 'restore' but like most things in Shorewall, that default can be changed. The default name is specified using the RESTOREFILE option in /etc/shorewall/shorewall.conf.