Operating Shorewall Tom Eastep 2006-06-03 2004 2005 2006 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. This article applies to Shorewall 3.0 and later. If you are running a version of Shorewall earlier than Shorewall 3.0.0 then please see the documentation for that release.
Operational Components There are a number of files that comprise the operational components of Shorewall. /sbin/shorewall — The program that you use to interact with Shorewall. Normally the root user's PATH includes /sbin and the program can be run from a shell prompt by simply typing shorewall followed by a command. In some releases of KDE, the default configuration of the konsole program is brain dead with respect to the "Root Console". It executes the command "su" where it should execute "su -"; the latter will cause a login shell to be created which will in turn set PATH properly. You can correct this problem as follows: Click on "Settings" on the toolbar and select "Configure Konsole" Select the "Session" tab. Click on "Root Console" Change the Execute command from "su" to "su -" Click on "Save Session" Click on "Ok" To see a list of supported commands, use the help command: shorewall help To get further information about a particular command, follow help by the command: shorewall help start /etc/shorewall — The default directory where Shorewall looks for configuration files. See the sections entitled Additional Configuration Directories and Alternate Configuration Directories for information about how you can direct Shorewall to look in other directories. /etc/init.d/shorewall (/etc/rc.d/firewall.rc on Slackware) — The script run by init (the program responsible for startup and shutdown of your system) to start Shorewall at boot time and to stop Shorewall at shutdown. /usr/share/shorewall/compiler — In Shorewall 3.1 and later, the program that processes your Shorewall configuration files and creates a script to start, stop, restart, restore and clear the firewall. /usr/share/shorewall/firewall — In Shorewall 3.0 and earlier, the program responsible for configuring Netfilter based on your configuration files. In 3.2 and later versions, this program implements the add, delete, stop, clear and refresh commands. /usr/share/shorewall/functions — A library of Bourne Shell functions used by /sbin/shorewall, /usr/share/shorewall/compiler and /usr/share/shorewall/firewall.
Starting, Stopping and Clearing As explained in the Introduction, Shorewall is not something that runs all of the time in your system. Nevertheless, for integrating Shorewall into your initialization scripts it is useful to speak of starting Shorewall and stopping Shorewall. Shorewall is started using the shorewall start command. Once the start command completes successfully, Netfilter is configured as described in your Shorewall configuration files. If there is an error during shorewall start, then if you have a saved configuration then that configuration is restored. Otherwise, an implicit shorewall stop is executed. Beginning with Shorewall 3.1, shorewall start is implemented as a compile and go; that is, the configuration is compiled and if there are no compilation errors then the resulting compiled script is executed. If there are compilation errors, the command is aborted and the state of the firewall is not altered. Shorewall is stopped using the shorewall stop command. The shorewall stop command does not remove all netfilter rules and open your firewall for all traffic to pass. It rather places your firewall in a safe state defined by the contents of your /etc/shorewall/routestopped file and the setting of ADMINISABSENTMINDED in /etc/shorewall/shorewall.conf. If you want to remove all Netfilter rules and open your firewall for all traffic to pass, use the shorewall clear command. If you change your configuration and want to install the changes, use the shorewall restart command. For additional information, see the Shorewall State Diagram section.
Tracing Command Execution If you include the word trace as the first parameter to an /sbin/shorewall command that transfers control to /usr/share/shorewall/firewall, execution of the latter program will be traced to STDERR. Tracing <command>shorewall start</command> To trace the execution of shorewall start and write the trace to the file /tmp/trace, you would enter:shorewall trace start 2> /tmp/trace
Having Shorewall Start Automatically at Boot Time The .rpm, .deb and .tgz all try to configure your startup scripts so that Shorewall will start automatically at boot time. If you are using the install.sh script from the .tgz and it cannot determine how to configure automatic startup, a message to that effect will be displayed. You will need to consult your distribution's documentation to see how to integrate the /etc/init.d/shorewall script into the distribution's startup mechanism. Shorewall startup is disabled by default. Once you have configured your firewall, you can enable startup by editing /etc/shorewall/shorewall.conf and setting STARTUP_ENABLED=Yes.. Note: Users of the .deb package must rather edit /etc/default/shorewall and set startup=1. If you use dialup or some flavor of PPP where your IP address can change arbitrarily, you may want to start the firewall in your /etc/ppp/ip-up.local script. I recommend just placing /sbin/shorewall restart in that script.
Saving a Working Configuration for Error Recovery and Fast Startup Once you have Shorewall working the way that you want it to, you can use shorewall save to save the commands necessary to recreate that configuration in a restore script. In its simplest form, the save command is just: shorewall save That command creates the default restore script, /var/lib/shorewall/restore. The default may be changed using the RESTOREFILE option in /etc/shorewall/shorewall.conf. A different file name may also be specified in the save command: shorewall save <filename> Where <filename> is a simple file name (no slashes). Once created, the default restore script serves several useful purposes: If you change your configuration and there is an error when you try to restart Shorewall, the restore script will be run to restore your firewall to working order. Bootup is faster. The -f option of the start command (e.g., shorewall -f start) causes Shorewall to look for the default restore script and if it exists, the script is run. This is much faster than starting Shorewall using the normal mechanism of reading the configuration files and running iptables dozens or even hundreds of times. By default, /etc/init.d/shorewall (/etc/rc.d/firewall.rc) uses the -f option when it is processing a request to start Shorewall. The shorewall restore command can be used at any time to quickly configure the firewall. shorewall restore [ <filename> ] If no <filename> is given, the default restore script is used. Otherwise, the script /var/lib/shorewall/<filename> is used. The ability to have multiple restore scripts means that you can save different Shorewall firewall configurations and switch between them quickly using the restore command. Restore scripts may be removed using the shorewall forget command: shorewall forget [ <filename> ] If no <filename> is given, the default restore script is removed. Otherwise, /var/lib/shorewall/<filename> is removed (of course, you can also use the Linux rm command from the shell prompt to remove these files).
Additional Configuration Directories The CONFIG_PATH setting in /etc/shorewall/shorewall.conf determines where Shorewall looks for configuration files. The default setting is CONFIG_PATH=/etc/shorewall:/usr/share/shorewall which means that /etc/shorewall is searched first and if the file is not found then /usr/share/shorewall is searched. You can change the value of CONFIG_PATH to cause additional directories to be searched but CONFIG_PATH should always include both /etc/shorewall and /usr/share/shorewall. When an alternate configuration directory is specified as described in the next section, that directory is searched before those directories listed in CONFIG_PATH. Example - Search /etc/shorewall, /etc/shorewall/actiondir and /usr/share/shorewall in that order: CONFIG_PATH=/etc/shorewall:/etc/shorewall/actiondir:/usr/share/shorewall The above is the setting that I once used to allow me to place all of my user-defined 'action.' files in /etc/shorewall/actiondir.
Alternate Configuration Directories As explained above, Shorewall normally looks for configuration files in the directories specified by the CONFIG_PATH option in /etc/shorewall/shorewall.conf. The shorewall start, shorewall restart, shorewall check, and shorewall try commands allow you to specify an additional directory for Shorewall to check before looking in the directories listed in CONFIG_PATH. shorewall {start|restart|check} <configuration-directory> shorewall try <configuration-directory> [ <timeout> ] If a <configuration-directory> is specified, each time that Shorewall is going to read a file, it will first look in the <configuration-directory> . If the file is present in the <configuration-directory>, that file will be used; otherwise, the directories in the CONFIG_PATH will be searched. When changing the configuration of a production firewall, I recommend the following: If you haven't saved the current working configuration, do so using shorewall save. mkdir /etc/test cd /etc/test <copy any files that you need to change from /etc/shorewall to . and change them here> shorewall check ./ <correct any errors found by check and check again> shorewall restart ./ If the restart fails, your configuration will be restored to it's state at the last shorewall save. When the new configuration works then just: cp -f * /etc/shorewall cd rm -rf /etc/test shorewall save
Command Reference The general form of a command in Shorewall 3.0 is:
shorewall [ <options> ] <command> [ <argument> ... ] Available options are: -c <directory> Specifies an alternate configuration directory. -f Specifies fast restart. See the start command below. -n Prevents the command from changing the firewall system's routing configuration. -q In Shorewall versions prior to 3.2.0, causes some of the output to be suppressed. In 3.2.0 and later, reduces the verbosity level (see VERBOSITY setting in shorewall.conf). May be repeated (e.g., "-qq") with each instance reducing the verbosity level by one. -v In Shorewall versions prior to 3.2.0, causes Ethernet MAC addresses to be included in log message displays. In 3.2.0 and later, increases the verbosity level (see VERBOSITY setting in shorewall.conf). May be repeated (e.g., "-qq") with each instance increasing the verbosity level by one. -x Causes all iptables -L commands to display actual packet and byte counts.
The general form of a command in Shorewall 3.1 and later is:
shorewall [ <options> ] <command> [ <command options> ] [ <argument> ... ] For compatibility, Shorewall 3.1 and later accept all of the 3.0 command options. In addition, 3.1 defines some new options and also defines command-specific options that are entered after the command on the run-line. New options are: -t All progress messages are timestamped with the date and time. In addition, the -q and -v options may be repeated to make the output less or more verbose respectively. The default level of verbosity is determined by the setting of the VERBOSITY option in /etc/shorewall/shorewall.conf.
Following in alphabetical order are the supported commands. add shorewall add <interface>[:<host-list>] … <zone> A <host-list> is a comma-separated list whose entries are: A host or network address The name of a bridge port The name of a bridge port followed by a colon (":") and a host or network address. Adds an interface (and list of hosts if included) to a dynamic zone usually used with VPN's. Example: shorewall add ipsec0:192.0.2.24 vpn1 adds the address 192.0.2.24 from interface ipsec0 to the zone vpn1. allow shorewall allow <address> ... Re-enables receipt of packets from hosts previously blacklisted by a drop or reject command. Shorewall allow, drop, rejct and save implement dynamic blacklisting. check shorewall check [ <configuration-directory> ] Performs a cursory validation of the zones, interfaces, hosts, rules, policy, masq, blacklist, proxyarp, nat and provider files. Use this if you are unsure of any edits you have made to the shorewall configuration. See above for a recommended way to make changes. clear shorewall clear Clear will remove all rules and chains installed by Shorewall. The firewall is then wide open and unprotected. Existing connections are untouched. Clear is often used to see if the firewall is causing connection problems. compile (Shorewall 3.1 and later) shorewall compile [ -e ] [ <directory name> ] <path name> Compiles the current configuration into the executable file <path name>. If <path name> names a file in /var/lib/shorewall then the file may be executed using the "restore" command. When -e is specified, the compilation is being performed on a system other than where the compiled script will run under Shorewall Lite. This option disables certain configuration options that require the script to be compiled where it is to be run and allows the script to be run on a system where Shorewall Lite is installed. The file /etc/shorewall/capabilities must be present when -e is used; that file specifies the iptables/kernel capabilities on the target system. The compiled script is a complete program that supports the following commands:
<program> [ -q ] [ -v ] [ -n ] start <program> [ -q ] [ -v ] [ -n ] stop <program> [ -q ] [ -v ] [ -n ] clear <program> [ -q ] [ -v ] [ -n ] restart <program> [ -q ] [ -v ] [ -n ] status <program> [ -q ] [ -v ] [ -n ] version
The options have their same meaning is when they are passed to /sbin/shorewall itself. For additional information about the compile command, see this article. delete shorewall delete <interface>[:<host-list>] … <zone> A <host-list> is a comma-separated list whose entries are: A host or network address The name of a bridge port The name of a bridge port followed by a colon (":") and a host or network address. Deletes the specified interface (and host list if included) from the specified zone. Example: shorewall delete ipsec0:192.0.2.24 vpn1 deletes the address 192.0.2.24 from interface ipsec0 from zone vpn1 drop shorewall drop <address> ... Causes packets from the specified <address> to be ignored dump shorewall [ -x ] dump Produce a verbose report about the firewall. When -x is given, that option is also passed to iptables to display actual packet and byte counts. forget shorewall forget [ <filename> ] Deletes /var/lib/shorewall/<filename>. If no <filename> is given then the file specified by RESTOREFILE in /etc/shorewall/shorewall.conf is removed. help shorewall help [<command> | host | address ] Display helpful information about the shorewall commands. hits hits Produces several reports about the Shorewall packet log messages in the current log file specified by the LOGFILE option in /etc/shorewall/shorewall.conf. ipcalc shorewall ipcalc { <address> <mask> | <address>/<vlsm> } Ipcalc displays the network address, broadcast address, network in CIDR notation and netmask corresponding to the input[s]. Example: ipcalc 192.168.1.0/24 iprange shorewall iprange <address1>-<address2> Iprange decomposes the specified range of IP addresses into the equivalent list of network/host addresses. logdrop shorewall logdrop <address> ... Causes packets from the specified <address> to be ignored and logged logwatch shorewall logwatch [ -m ] [<refresh interval>] Monitors the log file specified by theLOGFILE option in /etc/shorewall/shorewall.conf and produces an audible alarm when new Shorewall messages are logged. The '-m' option is available in Shorewall version 3.2.0 Beta5 and later and causes the MAC address of each packet source to be displayed if that information is available. logreject shorewall logreject <address> ... Causes packets from the specified <address> to be rejected and logged refresh shorewall [ -q ] refresh The rules involving the broadcast addresses of firewall interfaces, the black list and ECN control rules are recreated to reflect any changes made to your configuration files. Shorewall versions prior to 3.2.0 Beta 5 also recreate the traffic shaping rules as part of processing the refresh command. Existing connections are untouched. If -q is specified, less detail is displayed making it easier to spot warnings. reject shorewall reject <address> ... Causes packets from the specified <address>s to be rejected reset shorewall reset All the packet and byte counters in the firewall are reset. restart shorewall [ -q ] restart <configuration-directory> Restart is similar to shorewall stop followed by shorewall start. Existing connections are maintained. If -q is specified, less detail is displayed making it easier to spot warnings restore shorewall [ -q ] restore [ <filename> ] Restore Shorewall to a state saved using the shorewall save command Existing connections are maintained. The <filename> names a restore file in /var/lib/shorewall created using shorewall save; if no <filename> is given then Shorewall will be restored from the file specified by the RESTOREFILE option in /etc/shorewall/shorewall.conf. safe-restart shorewall [ -q ] safe-restart [ <filename> ] Only allowed if Shorewall is running. The current configuration is saved in /var/lib/shorewall/safe-restart (see the save command below) that a restart is done. You will then be prompted asking if you want to accept the new configuration or not. If you answer "n" or if you fail to answer within 60 seconds (such as when your new configuration has disabled communication with your terminal), the configuration is restored from the saved configuration. safe-start shorewall [ -q ] safe-start [ <filename> ] Shorewall is started normally. You will then be prompted asking if everything went all right. If you answer "n" or if you fail to answer within 60 seconds (such as when your new configuration has disabled communication with your terminal), a shorewall clear is performed for you. save shorewall save [ <filename> ] The dynamic data is stored in /var/lib/shorewall/save. The state of the firewall is stored in /var/lib/shorewall/<filename> for use by the shorewall restore and shorewall -f start commands. If <filename> is not given then the state is saved in the file specified by the RESTOREFILE option in /etc/shorewall/shorewall.conf. show shorewall [ -x ] show [ <chain> [ <chain> ...] |classifiers|connections|log|nat|tc|tos] shorewall [ -x ] show <chain> [ <chain> ... ] - produce a verbose report about the Netfilter chain(s). (iptables -L chain -n -v) shorewall [ -x ] show mangle - produce a verbose report about the mangle table. (iptables -t mangle -L -n -v) shorewall [ -x ] show nat - produce a verbose report about the nat table. (iptables -t nat -L -n -v) shorewall show [- m ] log - display the last 20 packet log entries. The '-m' option is available in Shorewall version 3.2.0 Beta5 and later and causes the MAC address of each packet source to be displayed if that information is available. shorewall show capabilities - Displays your kernel/iptables capabilities shorewall show connections - displays the IP connections currently being tracked by the firewall. shorewall show classifiers - displays information about the traffic control/shaping classifiers. shorewall show tc - displays information about the traffic control/shaping configuration. shorewall show zones — Displays the composition of each zone. When -x is given, that option is also passed to iptables to display actual packet and byte counts. start shorewall [ -q ] [ -f ] start [ <configuration-directory> ] Start shorewall. Existing connections through shorewall managed interfaces are untouched. New connections will be allowed only if they are allowed by the firewall rules or policies. If -q is specified, less detail is displayed making it easier to spot warnings If -f is specified, the saved configuration specified by the RESTOREFILE option in /etc/shorewall/shorewall.conf will be restored if that saved configuration exists stop shorewall stop Stops the firewall. All existing connections, except those listed in /etc/shorewall/routestopped or permitted by the ADMINISABSENTMINDED option in /etc/shorewall/shorewall.conf, are taken down. The only new traffic permitted through the firewall is from systems listed in /etc/shorewall/routestopped or by ADMINISABSENTMINDED. status shorewall status Produce a short report about the firewall's status and state relative to the diagram below. try (Deprecated) shorewall try <configuration-directory> [ <timeout> ] Restart shorewall using the specified configuration. If an error occurs during the restart, then another shorewall restart is performed using the default configuration. If a timeout is specified then the restart is always performed after the timeout occurs and uses the default configuration. When restarting using the default configuration, if the default restore script (as specified by the RESTOREFILE setting in /etc/shorewall/shorewall.conf) exists. then that script is used. version shorewall version Show the current shorewall version
Shorewall State Diagram The Shorewall State Diargram is depicted below. You will note that mose of the commands that result in state transitions use the word firewall rather than shorewall. That is because the actual transitions are done by /usr/share/shorewall/firewall; /sbin/shorewall runs firewall according to the following table: /sbin/shorewall Command Resulting /usr/share/shorewall/firewall Command Effect if the Command Succeeds shorewall start firewall start The system filters packets based on your current Shorewall Configuration shorewall stop firewall stop Only traffic to/from hosts listed in /etc/shorewall/hosts is passed to/from/through the firewall. If ADMINISABSENTMINDED=Yes in /etc/shorewall/shorewall.conf then in addition, all existing connections are retained and all connection requests from the firewall are accepted. shorewall restart firewall restart Logically equivalent to firewall stop;firewall start shorewall add firewall add Adds a host or subnet to a dynamic zone shorewall delete firewall delete Deletes a host or subnet from a dynamic zone shorewall refresh firewall refresh Reloads rules dealing with static blacklisting, traffic control and ECN. shorewall reset firewall reset Resets traffic counters shorewall clear firewall clear Removes all Shorewall rules, chains, addresses, routes and ARP entries. shorewall try firewall -c <new configuration> restart If unsuccessful then firewall start (standard configuration) If timeout then firewall restart (standard configuration) The only time that a program other than /usr/share/shorewall/firewall performs a state transition itself is when it executes the shorewall restore command is executed. In that case, the /var/lib/shorewall/restore program sets the state to "Started".
Notes for Shorewall 3.2.0 and Later With any command that involves compilation, there is no state transition while the compiler is running. If compilation fails, the state remains unchanged. Also, shorewall start and shorewall restart involve compilation followed by execution of the compiled script. So it is the compiled script that performs the state transition in these commands rather than /usr/share/shorewall/firewall. The compiled script is placed in /var/lib/shorewall and is named either .start or .restart depending on the command.