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Introduction to Shorewall

This is the Shorewall 1.4 Web Site

• The 1.3 site is here.
• The 1.2 site is here.

Glossary

• Netfilter - the packet filter facility built into the 2.4 and later Linux kernels.
• ipchains - the packet filter facility built into the 2.2 Linux kernels. Also the name of the utility program used to configure and control that facility. Netfilter can be used in ipchains compatibility mode.
• iptables - the utility program used to configure and control Netfilter. The term 'iptables' is often used to refer to the combination of iptables+Netfilter (with Netfilter not in ipchains compatibility mode).

What is Shorewall?

Getting Started with Shorewall

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License

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more detail.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA

Copyright © 2001-2003 Thomas M. Eastep

Running Shorewall on Mandrake with a two-interface setup?

News

12/07/2003 - Shorewall 1.4.9 Beta 1

Problems Corrected since version 1.4.8:

1. There has been a low continuing level of confusion over the terms "Source NAT" (SNAT) and "Static NAT". To avoid future confusion, all instances of "Static NAT" have been replaced with "One-to-one NAT" in the documentation and configuration files.
2. The description of NEWNOTSYN in shorewall.conf has been reworded for clarity.
3. Wild-card rules (those involving "all" as SOURCE or DEST) will no longer produce an error if they attempt to add a rule that would override a NONE policy. The logic for expanding these wild-card rules now simply skips those (SOURCE,DEST) pairs that have a NONE policy.

Migration Issues:
    None.

New Features:

1. To cut down on the number of "Why are these ports closed rather than stealthed?" questions, the SMB-related rules in /etc/shorewall/common.def have been changed from 'reject' to 'DROP'.
2. For easier identification, packets logged under the 'norfc1918' interface option are now logged out of chains named 'rfc1918'. Previously, such packets were logged under chains named 'logdrop'.
3. Distributors and developers seem to be regularly inventing new naming conventions for kernel modules. To avoid the need to change Shorewall code for each new convention, the MODULE_SUFFIX option has been added to shorewall.conf. MODULE_SUFFIX may be set to the suffix for module names in your particular distribution. If MODULE_SUFFIX is not set in shorewall.conf, Shorewall will use the list "o gz ko o.gz".
   
   To see what suffix is used by your distribution:
   
   ls /lib/modules/$(uname -r)/kernel/net/ipv4/netfilter
   
   All of the files listed should have the same suffix (extension). Set MODULE_SUFFIX to that suffix.
   
   Examples:
   
        If all files end in ".kzo" then set MODULE_SUFFIX="kzo"
        If all files end in ".kz.o" then set MODULE_SUFFIX="kz.o"
4. Support for user defined rule ACTIONS has been implemented through two new files:
   
   /etc/shorewall/actions - used to list the user-defined ACTIONS.
   /etc/shorewall/action.template - For each user defined <action>, copy this file to /etc/shorewall/action.<action> and add the appropriate rules for that <action>. Once an <action> has been defined, it may be used like any of the builtin ACTIONS (ACCEPT, DROP, etc.) in /etc/shorewall/rules.
   
   Example: You want an action that logs a packet at the 'info' level and accepts the connection.
   
   In /etc/shorewall/actions, you would add:
   
        LogAndAccept
   
   You would then copy /etc/shorewall/action.template to /etc/shorewall/LogAndAccept and in that file, you would add the two rules:
           LOG:info
           ACCEPT
   
   

12/03/2003 - Support Torch Passed

11/07/2003 - Shorewall 1.4.8

Problems Corrected since version 1.4.7:

1. Tuomo Soini has supplied a correction to a problem that occurs using some versions of 'ash'. The symptom is that "shorewall start" fails with:
    
      local: --limit: bad variable name
      iptables v1.2.8: Couldn't load match `-j':/lib/iptables/libipt_-j.so:
      cannot open shared object file: No such file or directory
      Try `iptables -h' or 'iptables --help' for more information.
2. Andres Zhoglo has supplied a correction that avoids trying to use the multiport match iptables facility on ICMP rules.
    
      Example of rule that previously caused "shorewall start" to fail:
    
              ACCEPT      loc  $FW  icmp    0,8,11,12
   
   
3. Previously, if the following error message was issued, Shorewall was left in an inconsistent state.
    
      Error: Unable to determine the routes through interface xxx
   
   
4. Handling of the LOGUNCLEAN option in shorewall.conf has been corrected.
5. In Shorewall 1.4.2, an optimization was added. This optimization involved creating a chain named "<zone>_frwd" for most zones defined using the /etc/shorewall/hosts file. It has since been discovered that in many cases these new chains contain redundant rules and that the "optimization" turns out to be less than optimal. The implementation has now been corrected.
6. When the MARK value in a tcrules entry is followed by ":F" or ":P", the ":F" or ":P" was previously only applied to the first Netfilter rule generated by the entry. It is now applied to all entries.
7. An incorrect comment concerning Debian's use of the SUBSYSLOCK option has been removed from shorewall.conf.
8. Previously, neither the 'routefilter' interface option nor the ROUTE_FILTER parameter were working properly. This has been corrected (thanks to Eric Bowles for his analysis and patch). The definition of the ROUTE_FILTER option has changed however. Previously, ROUTE_FILTER=Yes was documented as enabling route filtering on all interfaces (which didn't work). Beginning with this release, setting ROUTE_FILTER=Yes will enable route filtering of all interfaces brought up while Shorewall is started. As a consequence, ROUTE_FILTER=Yes can coexist with the use of the 'routefilter' option in the interfaces file.
9. If MAC verification was enabled on an interface with a /32 address and a broadcast address then an error would occur during startup.
10. he NONE policy's intended use is to suppress the generating of rules that can't possibly be traversed. This means that a policy of NONE is inappropriate where the source or destination zone is $FW or "all". Shorewall now generates an error message if such a policy is given in /etc/shorewall/policy. Previously such a policy caused "shorewall start" to fail.
11. The 'routeback' option was broken for wildcard interfaces (e.g., "tun+"). This has been corrected so that 'routeback' now works as expected in this case.
    

1. The definition of the ROUTE_FILTER option in shorewall.conf has changed as described in item 8) above.
   

1. A new QUEUE action has been introduced for rules. QUEUE allows you to pass connection requests to a user-space filter such as ftwall (http://p2pwall.sourceforge.net). The ftwall program allows for effective filtering of p2p applications such as Kazaa. For example, to use ftwall to filter P2P clients in the 'loc' zone, you would add the following rules:
   
      QUEUE   loc         net    tcp
      QUEUE   loc         net    udp
      QUEUE   loc         fw     udp
   
   You would normally want to place those three rules BEFORE any ACCEPT rules for loc->net udp or tcp.
   
   Note: When the protocol specified is TCP ("tcp", "TCP" or "6"), Shorewall will only pass connection requests (SYN packets) to user space. This is for compatibility with ftwall.
2. A BLACKLISTNEWNONLY option has been added to shorewall.conf. When this option is set to "Yes", the blacklists (dynamic and static) are only consulted for new connection requests. When set to "No" (the default if the variable is not set), the blacklists are consulted on every packet.
   
   Setting this option to "No" allows blacklisting to stop existing connections from a newly blacklisted host but is more expensive in terms of packet processing time. This is especially true if the blacklists contain a large number of entries.
3. Chain names used in the /etc/shorewall/accounting file may now begin with a digit ([0-9]) and may contain embedded dashes ("-").

10/26/2003 - Shorewall 1.4.7a and 1.4.7b win brown paper bag awards Shorewall 1.4.7c released.

1. The saga with "<zone>_frwd" chains continues. The 1.4.7c script produces a ruleset that should work for everyone even if it is not quite optimal. My apologies for this ongoing mess.
   

10/24/2003 - Shorewall 1.4.7b

This is a bugfx rollup of the 1.4.7a fixes plus:

1. The fix for problem 5 in 1.4.7a was wrong with the result that "<zone>_frwd" chains might contain too few rules. That wrong code is corrected in this release.
   

10/21/2003 - Shorewall 1.4.7a

This is a bugfix rollup of the following problem corrections:

1. Tuomo Soini has supplied a correction to a problem that occurs using some versions of 'ash'. The symptom is that "shorewall start" fails with:
    
      local: --limit: bad variable name
      iptables v1.2.8: Couldn't load match `-j':/lib/iptables/libipt_-j.so:
      cannot open shared object file: No such file or directory
      Try `iptables -h' or 'iptables --help' for more information.
   
   
2. Andres Zhoglo has supplied a correction that avoids trying to use the multiport match iptables facility on ICMP rules.
    
      Example of rule that previously caused "shorewall start" to fail:
    
              ACCEPT      loc  $FW  icmp    0,8,11,12
   
   
3. Previously, if the following error message was issued, Shorewall was left in an inconsistent state.
    
      Error: Unable to determine the routes through interface xxx
   
   
4. Handling of the LOGUNCLEAN option in shorewall.conf has been corrected.
5. In Shorewall 1.4.2, an optimization was added. This optimization involved creating a chain named "<zone>_frwd" for most zones defined using the /etc/shorewall/hosts file. It has since been discovered that in many cases these new chains contain redundant rules and that the "optimization" turns out to be less than optimal. The implementation has now been corrected.
6. When the MARK value in a tcrules entry is followed by ":F" or ":P", the ":F" or ":P" was previously only applied to the first Netfilter rule generated by the entry. It is now applied to all entries.
   

More News

Jacques Nilo and Eric Wolzak have a LEAF (router/firewall/gateway on a floppy, CD or compact flash) distribution called Bering that features Shorewall-1.4.2 and Kernel-2.4.20. You can find their work at: http://leaf.sourceforge.net/devel/jnilo

Donations

Shorewall is free but if you try it and find it useful, please consider making a donation to Starlight Children's Foundation. Thanks!