Dynamic Zones

Dynamic Zones Tom Eastep 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.

Overview 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.

Installing 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'

Dynamic Zones -- Shorewall 4.5.9 and Later Prior to Shorewall 4.5.9, when multiple records for a zone appear in /etc/shorewall/hosts, Shorewall would create a separate ipset for each interface. This meant that an add or delete command was required for each of the interface, when the address involved was reachable via multiple interfaces. Beginning with Shoreawll 4.5.9, it is possible to have a single ipset shared among all interfaces. This also simplifies management of dynamic zone contents for dynamic zones associated with only a single interface. The earlier implementation described below is still available in these later releases.

Defining a Dynamic Zone A dynamic zone is defined by specifying the dynamic_shared option in the zones file and using the dynamic keyword in the hosts list. /etc/shorewall/zones:#NAME TYPE OPTIONS net ipv4 rsyncok:loc ipv4 dynamic_shared/etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS loc eth0 - … loc eth1 - … /etc/shorewall/hosts: #ZONE HOSTS OPTIONS rsyncok eth0:dynamic rsyncok eth1:dynamic When the dynamic_shared option is specified, a single ipset is created; the ipset has the same name as the zone.

Adding a Host to a Dynamic Zone. 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 zone address ...

Example:

shorewall add rsyncok 70.90.191.124

Deleting a Host from a Dynamic Zone 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 zone address ...

Example:

shorewall delete rsyncok 70.19.191.124

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.

Listing the Contents of a Dynamic Zone The shorewall show command may be used to list the current contents of a dynamic zone.

shorewall show dynamic zone

Example:

shorewall show dynamic rsyncok rsyncok: 70.90.191.122 70.90.191.124

Dynamic Zones -- Shorewall 5.4.8 and Earlier. The method described in this section is still supported in the later releases.

Defining a Dynamic Zone 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. The dynamic zone capability was added to Shorewall6 in Shorewall 4.4.21.

Adding a Host to a Dynamic Zone 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 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 ipse t command must be used directly.

Listing the Contents of a Dynamic Zone 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: 192.168.3.4 192.168.3.9

Dynamic Zone Contents and Shorewall stop/start/restart When SAVE_IPSETS=Yes in shorewall.conf, the 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.