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'
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.
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 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 webok
eth0:
192.168.3.4
192.168.3.9
Dynamic Zone Contents and Shorewall stop/start/restart
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.
Restrictions
When using dynamic zones, you may not use ipsets in your /etc/shorewall/routestopped
file.