Copyright © 2009 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”.
2010/01/31
Table of Contents
There is sometimes a need to be able to define a zone whose members are unknown at compile-time. For example, you may wish to require authentication of internal users before allowing them access to the internet. When a user is authenticated, the user's IP address is added to the zone of users permitted web access.
Shorewall provides basic support for defining such zones. This support is based on ipset. As of this writing, ipset is not included in the standard kernel distribution; so to use dynamic zones, you must be running kernel 2.6.20 or later and have installed the xtables-addons.
The xtables-addons are fairly easy to install. You do not need to recompile your kernel.
Debian™ users can find xtables-addons-common and xtables-addons-source packages in testing. The kernel modules can be built and installed with the help of module-assistant. As of this writing, these packages are in the admin group rather than in the network group!!??
For other users, the basic steps are as follows:
Install gcc and make
Install the headers for the kernel you are running. In some distributions, such as Debian™ and Ubuntu™, the packet is called kernel-headers. For other distrubutions, such as OpenSuSE, you must install the kernel-source package.
download the iptables source tarball
untar the source
cd to the iptables source directory
run 'make'
as root, run 'make install'
Your new iptables binary will now be installed in /usr/local/sbin. Modify shorewall.conf to specify IPTABLES=/usr/local/sbin/iptables
Download the latest xtables-addons source tarball
Untar the xtables-addons source
cd to the xtables-addons source directory
run './configure'
run 'make'
As root, cd to the xtables-addons directory and run 'make install'.
Restart shorewall
'shorewall show capabilities' should now indicate Ipset Match: Available
You will have to repeat steps 10-13 each time that you receive a kernel upgrade from your distribution vendor. You can install xtables-addons before booting to the new kernel as follows (new-kernel-version is the version of the newly-installed kernel - example 2.6.28.11-generic. Look in the /lib/modules directory to get the full version name)
cd to the xtables-addons source directory
run 'make clean'
run './configure --with-kbuild=/lib/modules/new-kernel-version/build --with-ksource=/lib/modules/new-kernel-version/source'
run 'make'
As root, cd to the xtables-addons source directory and run 'make install'.
As root, run 'depmod -a new-kernel-version'
A dynamic zone is defined by using the keyword dynamic in the zones host list.
Example:
/etc/shorewall/zones:#NAME TYPE OPTIONS loc ipv4 webok:loc ipv4
/etc/shorewall/interfaces:#ZONE INTERFACE BROADCAST OPTIONS loc eth0 - …
/etc/shorewall/hosts:#ZONE HOSTS OPTIONS webok eth0:dynamic
Once the above definition is added, Shorewall will automatically create an ipset named webok_eth0 the next time that Shorewall is started or restarted. Shorewall will create an ipset of type iphash. If you want to use a different type of ipset, such as macipmap, then you will want to manually create that ipset yourself before the next Shorewall start/restart.
Adding a host to a dynamic zone is accomplished by adding the host's IP address to the appropriate ipset. Shorewall provldes a command for doing that:
shorewall add
interface:address ...zone
Example:
shorewall add eth0:192.168.3.4 webok
The command can only be used when the ipset involved is of type iphash. For other ipset types, the ipset command must be used directly.
Deleting a host from a dynamic zone is accomplished by removing the host's IP address from the appropriate ipset. Shorewall provldes a command for doing that:
shorewall delete
interface:address ...zone
Example:
shorewall delete eth0:192.168.3.4 webok
The command can only be used when the ipset involved is of type iphash. For other ipset types, the ipset command must be used directly.
The shorewall show command may be used to list the current contents of a dynamic zone.
shorewall show dynamic
zone
Example:
shorewall show dynamic webok
eth0:
192.168.3.4
192.168.3.9The contents of a dynamic zone survive shorewall
stop/shorewall start and shorewall restart.
During shorewall stop, the contents of the ipsets are
saved in the file ${VARDIR}/ipsets.save (usually
/var/lib/shorewall/ipsets.save). During
shorewall start, the contents of that file are restored
to the sets. During both shorewall start and
shorewall restart, any new ipsets required as a result
of a configuration change are added.
When using dynamic zones, you may not use ipsets in your /etc/shorewall/routestopped file.