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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>Xen and the Art of Consolidation</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate>2006-06-05</pubdate>
<copyright>
<year>2006</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<legalnotice>
<para>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
<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<caution>
<para>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.</para>
</caution>
<section>
<title>Before Xen</title>
<para>Prior to adopting <ulink url="Xen.html">Xen</ulink>, I had a home
office crowded with 5 systems, three monitors a scanner and a printer. The
systems were:</para>
<orderedlist>
<listitem>
<para>Firewall</para>
</listitem>
<listitem>
<para>Public Server in a DMZ (mail)</para>
</listitem>
<listitem>
<para>Private Server (wookie)</para>
</listitem>
<listitem>
<para>My personal Linux Desktop (ursa)</para>
</listitem>
<listitem>
<para>My work system (docked laptop running Windows XP).</para>
</listitem>
</orderedlist>
<para>The result was a very crowded and noisy room.</para>
</section>
<section>
<title>After Xen</title>
<para>Xen has allowed me to reduce the noise and clutter considerably. I
now have three systems with two monitors. I've also replaced the
individual printer and scanner with a Multifunction
FAX/Scanner/Printer.</para>
<para>The systems now include:</para>
<orderedlist>
<listitem>
<para>Combination Firewall/Public Server/Private Server/Wireless
Gateway using Xen (created by building out my Linux desktop
system).</para>
</listitem>
<listitem>
<para>My work system.</para>
</listitem>
<listitem>
<para>My Linux desktop (wookie, which is actually the old public
server box)</para>
</listitem>
</orderedlist>
<para>Most of the Linux systems run SUSE 10.0 or SUSE 10.1; my personal
Linux desktop system runs Ubuntu "Dapper Drake".</para>
<para>If you are unfamiliar with Xen networking, I recommend that you read
the first section of the companion <ulink url="Xen.html">Xen and
Shorewall</ulink> article.</para>
<para>Here is a high-level diagram of our network.</para>
<graphic align="center" fileref="images/Xen5.png" />
<para>As shown in this diagram, the Xen system has three physical network
interfaces. These are:</para>
<itemizedlist>
<listitem>
<para><filename class="devicefile">eth0</filename> -- conntected to
the switch in my office. That switch is cabled to a second switch in
my wife's office where my wife has her desktop and networked printer
(I sure wish that there had been wireless back when I strung that
CAT-5 cable halfway across the house).</para>
</listitem>
<listitem>
<para><filename class="devicefile">eth1</filename> -- connected to our
DSL "Modem".</para>
</listitem>
<listitem>
<para><filename class="devicefile">eth2</filename> -- connected to a
Wireless Access Point (WAP) that interfaces to our wireless
network.</para>
</listitem>
</itemizedlist>
<para>There are four Xen domains.</para>
<orderedlist>
<listitem>
<para>Dom0 (DNS name ursa.shorewall.net) is used as a local file
server (NFS and Samba).</para>
</listitem>
<listitem>
<para>The first DomU (Dom name <emphasis
role="bold">firewall</emphasis>, DNS name gateway.shorewall.net) is
used as our main firewall.</para>
</listitem>
<listitem>
<para>The second DomU (Dom name <emphasis
role="bold">lists</emphasis>, DNS name lists.shorewall.net) is used as
a public Web/FTP/Mail/DNS server.</para>
</listitem>
<listitem>
<para>The third DomU (Dom name <emphasis
role="bold">wireless</emphasis>, DNS name wireless.shorewall.net) is
used as a gateway to our wireless network.</para>
</listitem>
</orderedlist>
<para>A seperate wireless gateway is necessary because Xen 3.0 only
supports three virtual interfaces per DomU and the firewall DomU already
has three interfaces. Shorewall runs in Dom0, in the firewall domain and
in the wireless gateway.</para>
<caution>
<para>As the developer of Shorewall, I have enough experience to be very
comfortable with Linux networking and Shorewall/iptables. I arrived at
this configuration after a lot of trial and error experimentation (see
<ulink url="Xen.html">Xen and Shorewall</ulink>). If you are a Linux
networking novice, I recommend that you do not attempt a configuration
like this one for your first Shorewall installation. You are very likely
to frustrate both yourself and the Shorewall support team. Rather I
suggest that you start with something simple like a <ulink
url="standalone.htm">standalone installation</ulink> in a domU; once you
are comfortable with that then you will be ready to try something more
substantial.</para>
<para>As Paul Gear says: <emphasis>Shorewall might make iptables easy,
but it doesn't make understanding fundamental networking principles,
traffic shaping, or multi-ISP routing any easier</emphasis>.</para>
<para>The same goes for Xen networking.</para>
</caution>
<section id="Domains">
<title>Domain Configuration</title>
<para>Below are the relevant configuration files for the four domains.
The "loopback.nloopbacks=..." entries are used to restrict the number of
"veth<emphasis>n</emphasis>" devices that the Xen kernel creates. I use
partitions on my hard drives for DomU storage devices.</para>
<blockquote>
<para><filename>/boot/grub/menu.lst</filename> — here is the entry
that boots Xen in Dom0.</para>
<programlisting>title XEN
root (hd0,1)
kernel /boot/xen.gz dom0_mem=458752 sched=bvt
module /boot/vmlinuz-xen root=/dev/hda2 vga=0x31a selinux=0 resume=/dev/hda1 splash=silent showopts loopback.nloopbacks=1
module /boot/initrd-xen</programlisting>
<para><filename>/etc/xen/auto/01-firewall</filename> — configuration
file for the firewall domain</para>
<programlisting># -*- mode: python; -*-
# configuration name:
name = "firewall"
# usable ram:
memory = 256
# kernel and initrd:
kernel = "/boot/vmlinuz-xen"
ramdisk = "/boot/initrd-xen"
# boot device:
root = "/dev/hdb2"
# boot to run level:
extra = "loopback.nloopbacks=0 3"
# network interface:
vif = [ 'mac=aa:cc:00:00:00:02, bridge=xenbr0', 'mac=aa:cc:00:00:00:03, bridge=xenbr1' , 'mac=00:a0:cc:63:66:89, bridge=xenbr2' ]
hostname = name
# storage devices:
disk = [ 'phy:hdb2,hdb2,w' ]</programlisting>
<para><filename>/etc/xen/auto/02-lists</filename> — configuration file
for the lists domain</para>
<programlisting># -*- mode: python; -*-
# configuration name:
name = "lists"
# usable ram:
memory = 512
# kernel and initrd:
kernel = "/boot/vmlinuz-xen"
ramdisk = "/boot/initrd-xen"
# boot device:
root = "/dev/hda3"
# boot to run level:
extra = "loopback.nloopbacks=0 3"
# network interface:
vif = [ 'mac=aa:cc:00:00:00:01, bridge=xenbr1' ]
hostname = name
# storage devices:
disk = [ 'phy:hda3,hda3,w' ]</programlisting>
<para>/etc/xen/auto/03-wireless — configuration file for the wireless
domain.</para>
<programlisting># -*- mode: python; -*-
# configuration name:
name = "wireless"
# usable ram:
memory = 256
# kernel and initrd:
kernel = "/boot/vmlinuz-xen"
ramdisk = "/boot/initrd-xen"
# boot device:
root = "/dev/hdb4"
# boot to run level:
extra = "loopback.nloopbacks=0 3"
# network interface:
vif = [ 'mac=aa:cc:00:00:00:04, bridge=xenbr0', 'mac=00:a0:cc:d1:db:12, bridge=xenbr3' ]
dhcp = 'dhcp'
hostname = name
# storage devices:
disk = [ 'phy:hdb4,hdb4,w' ]</programlisting>
</blockquote>
<para>With all four Xen domains up and running, the system looks as
shown in the following diagram.</para>
<graphic align="center" fileref="images/Xen4.png" />
<para>The zones correspond to the Shorewall zones in the Dom0
configuration.</para>
<caution>
<para>Under some circumstances, UDP and/or TCP communication from a
domU won't work for no obvious reason. That happened with the
<emphasis role="bold">lists</emphasis> domain in my setup. Looking at
the IP traffic with <command>tcpdump -nvvi eth1</command> in the
<emphasis role="bold">firewall</emphasis> domU showed that UDP packets
from the <emphasis role="bold">lists</emphasis> domU had incorrect
checksums. That problem was corrected by arranging for the following
command to be executed in the <emphasis role="bold">lists</emphasis>
domain when its <filename class="devicefile">eth0</filename> device
was brought up:</para>
<para><command>ethtool -K eth0 tx off</command></para>
</caution>
<para>SuSE 10.0 includes Xen 3.0 which does not support PCI
delegation<footnote>
<para>PCI delegation was a feature of Xen 2.0 but that capability
was dropped in 3.0. It has been restored in Xen 3.0.2 and once I
upgrade this system to SUSE 10.1 (which includes Xen 3.0.2), I
intend to implement PCI delegation and remove three of the four
bridges. I will probably combine the wireless and firewall domains
at that time as well.</para>
</footnote>; I therefore use a bridged configuration with four bridges
(one for each network interface). When Shorewall starts during bootup of
Dom0, it creates the four bridges using this
<filename>/etc/shorewall/init</filename> extension script:</para>
<blockquote>
<programlisting>for bridge in xenbr0 xenbr1 xenbr2 xenbr3; do
if [ -z "$(/sbin/brctl show 2&gt; /dev/null | fgrep $bridge)" ]; then
/sbin/brctl addbr $bridge
case $bridge in
xenbr2)
mac=`ip link show eth1 | grep 'link\/ether' | sed -e 's/.*ether \(..:..:..:..:..:..\).*/\1/'`
[ "$mac" = "fe:ff:ff:ff:ff:ff" ] || /sbin/ip link set dev eth1 addr fe:ff:ff:ff:ff:ff
/sbin/ip link set dev eth1 up
/sbin/brctl addif xenbr2 eth1
;;
xenbr3)
mac=`ip link show eth2 | grep 'link\/ether' | sed -e 's/.*ether \(..:..:..:..:..:..\).*/\1/'`
[ "$mac" = "fe:ff:ff:ff:ff:ff" ] || /sbin/ip link set dev eth2 addr fe:ff:ff:ff:ff:ff
/sbin/ip link set dev eth2 up
/sbin/brctl addif xenbr3 eth2
;;
esac
/sbin/ip link set dev $bridge up
fi
done</programlisting>
</blockquote>
</section>
<section id="Dom0">
<title>Dom0 Configuration</title>
<para>The goals for the Shorewall configuration in Dom0 are as
follows:</para>
<itemizedlist>
<listitem>
<para>Allow traffic to flow unrestricted through the four bridges.
This is done by configuring the hosts connected to each bridge as a
separate zone and relying on Shorewall's implicit intra-zone ACCEPT
policy to permit traffic through the bridge.</para>
</listitem>
<listitem>
<para>Ensure that there is no stray traffic between the zones. This
is a "belt+suspenders" measure since there should be no routing
between the bridges (because they don't have IP addresses).</para>
</listitem>
</itemizedlist>
<para>The configuration is a simple one:</para>
<blockquote>
<para><filename>/etc/shorewall/zones</filename>:</para>
<programlisting>#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
fw firewall
Wifi ipv4
loc ipv4
dmz ipv4
net ipv4
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE
</programlisting>
<para><filename>/etc/shorewall/policy</filename> (Note the unusual use
of an ACCEPT all-&gt;all policy):</para>
<programlisting>#SOURCE DEST POLICY LOG LIMIT:BURST
# LEVEL
Wifi all REJECT info
all Wifi REJECT info
dmz all REJECT info
all dmz REJECT info
net all REJECT info
all net REJECT info
all all ACCEPT
#LAST LINE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/interfaces</filename>:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
Wifi xenbr3 - routeback
loc xenbr0 192.168.1.255 dhcp,routeback
dmz xenbr1 - routeback
net xenbr2 - routeback
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/rules</filename>:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST SOURCE ORIGINAL RATE USER/
# PORT PORT(S) DEST LIMIT GROUP
#SECTION ESTABLISHED
#SECTION RELATED
SECTION NEW
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
</blockquote>
</section>
<section id="Firewall">
<title>Firewall DomU Configuration</title>
<para>In the firewall DomU, I run a conventional three-interface
firewall with Proxy ARP DMZ -- it is very similar to the firewall
described in the <ulink url="shorewall_setup_guide.htm">Shorewall Setup
Guide</ulink>. The firewall runs a routed <ulink
url="OPENVPN.html">OpenVPN server</ulink> to provide roadwarrior access
for our two laptops. Here is the firewall's view of the network:</para>
<graphic align="center" fileref="images/network4.png" />
<para>The two laptops can be directly attached to the LAN as shown above
or they can be attached wirelessly through the <link
linkend="Wireless">wireless gateway</link> -- their IP addresses are the
same in either case; when they are directly attached, the IP address is
assigned by the DHCP server running on the firewall and when they are
attached wirelessly, the IP address is assigned by OpenVPN.</para>
<para>The Shorewall configuration files are shown below. All routing and
secondary IP addresses are handled in the SUSE network
configuration.</para>
<blockquote>
<para>/etc/shorewall/shorewall.conf:</para>
<programlisting>STARTUP_ENABLED=Yes
VERBOSITY=0
LOGFILE=/var/log/firewall
LOGFORMAT="Shorewall:%s:%s:"
LOGTAGONLY=No
LOGRATE=
LOGBURST=
LOGALLNEW=
BLACKLIST_LOGLEVEL=
MACLIST_LOG_LEVEL=$LOG
TCP_FLAGS_LOG_LEVEL=$LOG
RFC1918_LOG_LEVEL=$LOG
SMURF_LOG_LEVEL=$LOG
LOG_MARTIANS=No
IPTABLES=/usr/sbin/iptables
PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/bin:/usr/local/sbin
SHOREWALL_SHELL=/bin/bash
SUBSYSLOCK=
MODULESDIR=
CONFIG_PATH=/etc/shorewall:/usr/share/shorewall
RESTOREFILE=standard
IPSECFILE=zones
IP_FORWARDING=On
ADD_IP_ALIASES=No
ADD_SNAT_ALIASES=No
RETAIN_ALIASES=No
TC_ENABLED=Internal
CLEAR_TC=Yes
MARK_IN_FORWARD_CHAIN=Yes
CLAMPMSS=Yes
ROUTE_FILTER=No
DETECT_DNAT_IPADDRS=Yes
MUTEX_TIMEOUT=60
ADMINISABSENTMINDED=Yes
BLACKLISTNEWONLY=Yes
DELAYBLACKLISTLOAD=No
MODULE_SUFFIX=
DISABLE_IPV6=Yes
BRIDGING=No
DYNAMIC_ZONES=No
PKTTYPE=No
RFC1918_STRICT=Yes
MACLIST_TTL=60
SAVE_IPSETS=No
MAPOLDACTIONS=No
FASTACCEPT=Yes
BLACKLIST_DISPOSITION=DROP
MACLIST_TABLE=mangle
MACLIST_DISPOSITION=DROP
TCP_FLAGS_DISPOSITION=DROP</programlisting>
<para><filename>/etc/shorewall/zones</filename>:</para>
<programlisting>#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
fw firewall
net ipv4 #Internet
loc ipv4 #Local wired Zone
dmz:loc ipv4 #DMZ -- server running in virtual machine at 206.124.146.177
vpn ipv4 #Open VPN clients
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE
</programlisting>
<para><filename>/etc/shorewall/policy</filename>:</para>
<programlisting>#SOURCE DEST POLICY LOG LIMIT:BURST
# LEVEL
$FW $FW ACCEPT
$FW net ACCEPT
loc net ACCEPT
$FW vpn ACCEPT
vpn net ACCEPT
vpn loc ACCEPT
loc vpn ACCEPT
$FW loc ACCEPT
loc $FW REJECT $LOG
net all DROP $LOG 10/sec:40
all all REJECT $LOG
#LAST LINE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/params (edited)</filename>:</para>
<programlisting>MIRRORS=&lt;comma-separated list of Shorewall mirrors&gt;
NTPSERVERS=&lt;comma-separated list of NTP servers I sync with&gt;
POPSERVERS=&lt;comma-separated list of server IP addresses&gt;
LOG=info
INT_IF=eth0
DMZ_IF=eth1
EXT_IF=eth3
OMAK=&lt;IP address at our second home&gt;
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/init</filename>:</para>
<programlisting>echo 1 &gt; /proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_be_liberal</programlisting>
<para><filename>/etc/shorewall/interfaces</filename>:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
net $EXT_IF 206.124.146.255 dhcp,norfc1918,logmartians,blacklist,tcpflags,nosmurfs
dmz $DMZ_IF 192.168.0.255 logmartians
loc $INT_IF 192.168.1.255 dhcp,routeback,logmartians
vpn tun+ -
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/nat</filename>:</para>
<programlisting>#EXTERNAL INTERFACE INTERNAL ALL LOCAL
# INTERFACES
206.124.146.178 $EXT_IF 192.168.1.3 No No
206.124.146.180 $EXT_IF 192.168.1.6 No No
#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/masq (Note the cute trick here and in
the <filename>proxyarp</filename> file that follows that allows me to
access the DSL "Modem" using it's default IP address
(192.168.1.1))</filename>:</para>
<programlisting>#INTERFACE SUBNET ADDRESS PROTO PORT(S) IPSEC
+$EXT_IF:192.168.1.1 0.0.0.0/0 192.168.1.254
$EXT_IF 192.168.0.0/22 206.124.146.179
#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/proxyarp</filename>:</para>
<programlisting>#ADDRESS INTERFACE EXTERNAL HAVEROUTE PERSISTENT
192.168.1.1 $EXT_IF $INT_IF yes
206.124.146.177 $DMZ_IF $EXT_IF yes
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/tunnels</filename>:</para>
<programlisting>#TYPE ZONE GATEWAY GATEWAY
# ZONE
openvpnserver:udp net 0.0.0.0/0
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/actions</filename>:</para>
<programlisting>#ACTION
Mirrors # Accept traffic from Shorewall Mirrors
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/action.Mirrors</filename>:</para>
<programlisting>#TARGET SOURCE DEST PROTO DEST SOURCE ORIGINAL RATE
# PORT PORT(S) DEST LIMIT
ACCEPT $MIRRORS
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/rules</filename>:</para>
<programlisting>SECTION NEW
###############################################################################################################################################################################
#ACTION SOURCE DEST PROTO DEST SOURCE ORIGINAL RATE USER/
# PORT PORT(S) DEST LIMIT GROUP
###############################################################################################################################################################################
REJECT:$LOG loc net tcp 25
REJECT:$LOG loc net udp 1025:1031
#
# Stop NETBIOS crap
#
REJECT loc net tcp 137,445
REJECT loc net udp 137:139
#
# Stop my idiotic work laptop from sending to the net with an HP source/dest IP address
#
DROP loc:!192.168.0.0/22 net
###############################################################################################################################################################################
# Local Network to Firewall
#
DROP loc:!192.168.0.0/22 fw # Silently drop traffic with an HP source IP from my XP box
ACCEPT loc fw tcp 22
ACCEPT loc fw tcp time,631,8080
ACCEPT loc fw udp 161,ntp,631
ACCEPT loc:192.168.1.5 fw udp 111
DROP loc fw tcp 3185 #SUSE Meta pppd
Ping/ACCEPT loc fw
REDIRECT loc 3128 tcp 80 - !206.124.146.177
###############################################################################################################################################################################
# Road Warriors to Firewall
#
ACCEPT vpn fw tcp ssh,time,631,8080
ACCEPT vpn fw udp 161,ntp,631
Ping/ACCEPT vpn fw
###############################################################################################################################################################################
# Road Warriors to DMZ
#
ACCEPT vpn dmz udp domain
ACCEPT vpn dmz tcp www,smtp,smtps,domain,ssh,imap,https,imaps,ftp,10023,pop3 -
Ping/ACCEPT vpn dmz
###############################################################################################################################################################################
# Local network to DMZ
#
ACCEPT loc dmz udp domain
ACCEPT loc dmz tcp ssh,smtps,www,ftp,imaps,domain,https -
ACCEPT loc dmz tcp smtp
Trcrt/ACCEPT loc dmz
###############################################################################################################################################################################
# Internet to ALL -- drop NewNotSyn packets
#
dropNotSyn net fw tcp
dropNotSyn net loc tcp
dropNotSyn net dmz tcp
###############################################################################################################################################################################
# Internet to DMZ
#
ACCEPT net dmz udp domain
LOG:$LOG net:64.126.128.0/18 dmz tcp smtp
ACCEPT net dmz tcp smtps,www,ftp,imaps,domain,https -
ACCEPT net dmz tcp smtp - 206.124.146.177,206.124.146.178
ACCEPT net dmz udp 33434:33454
Mirrors net dmz tcp rsync
Limit:$LOG:SSHA,3,60\
net dmz tcp 22
Trcrt/ACCEPT net dmz
##############################################################################################################################################################################
#
# Net to Local
#
# When I'm "on the road", the following two rules allow me VPN access back home using PPTP.
#
DNAT net loc:192.168.1.4 tcp 1729
DNAT net loc:192.168.1.4 gre
#
# Roadwarrior access to Wookie
#
ACCEPT net:$OMAK loc tcp 22
Limit:$LOG:SSHA,3,60\
net loc tcp 22
#
# ICQ
#
ACCEPT net loc:192.168.1.3 tcp 113,4000:4100
#
# Bittorrent
#
ACCEPT net loc:192.168.1.3 tcp 6881:6889,6969
ACCEPT net loc:192.168.1.3 udp 6881:6889,6969
#
# Real Audio
#
ACCEPT net loc:192.168.1.3 udp 6970:7170
#
# Skype
#
ACCEPT net loc:192.168.1.6 tcp 1194
#
# Traceroute
#
Trcrt/ACCEPT net loc:192.168.1.3
#
# Silently Handle common probes
#
REJECT net loc tcp www,ftp,https
DROP net loc icmp 8
###############################################################################################################################################################################
# DMZ to Internet
#
ACCEPT dmz net udp domain,ntp
ACCEPT dmz net tcp echo,ftp,ssh,smtp,whois,domain,www,81,https,cvspserver,2702,2703,8080
ACCEPT dmz net:$POPSERVERS tcp pop3
Ping/ACCEPT dmz net
#
# Some FTP clients seem prone to sending the PORT command split over two packets. This prevents the FTP connection tracking
# code from processing the command and setting up the proper expectation. The following rule allows active FTP to work in these cases
# but logs the connection so I can keep an eye on this potential security hole.
#
ACCEPT:$LOG dmz net tcp 1024: 20
###############################################################################################################################################################################
# Local to DMZ
#
ACCEPT loc dmz udp domain,xdmcp
ACCEPT loc dmz tcp www,smtp,smtps,domain,ssh,imap,rsync,https,imaps,ftp,10023,pop3,3128
Trcrt/ACCEPT loc dmz
###############################################################################################################################################################################
# DMZ to Local
#
ACCEPT dmz loc:192.168.1.5 udp 123
ACCEPT dmz loc:192.168.1.5 tcp 21
Ping/ACCEPT dmz loc
###############################################################################################################################################################################
# DMZ to Firewall -- ntp &amp; snmp, Silently reject Auth
#
ACCEPT dmz fw tcp 161,ssh
ACCEPT dmz fw udp 161
REJECT dmz fw tcp auth
Ping/ACCEPT dmz fw
###############################################################################################################################################################################
# Internet to Firewall
#
REJECT net fw tcp www,ftp,https
DROP net fw icmp 8
ACCEPT net fw udp 33434:33454
ACCEPT net:$OMAK fw udp ntp
ACCEPT net fw tcp auth
ACCEPT net:$OMAK fw tcp 22
Limit:$LOG:SSHA,3,60\
net fw tcp 22
Trcrt/ACCEPT net fw
###############################################################################################################################################################################
# Firewall to DMZ
#
ACCEPT fw dmz tcp domain,www,ftp,ssh,smtp,https,993,465
ACCEPT fw dmz udp domain
REJECT fw dmz udp 137:139
Ping/ACCEPT fw dmz
##############################################################################################################################################################################
# Avoid logging Freenode.net probes
#
DROP net:82.96.96.3 all
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/tcdevices</filename></para>
<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH
$EXT_IF 1.3mbit 384kbit
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE
</programlisting>
<para><filename>/etc/shorewall/tcclasses</filename><programlisting>#INTERFACE MARK RATE CEIL PRIORITY OPTIONS
$EXT_IF 10 full full 1 tcp-ack,tos-minimize-delay
$EXT_IF 20 9*full/10 9*full/10 2 default
$EXT_IF 30 6*full/10 6*full/10 3
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting></para>
<para><filename>/etc/shorewall/tcrules</filename><programlisting>#MARK SOURCE DEST PROTO PORT(S) CLIENT USER TEST
# PORT(S)
1:110 192.168.0.0/22 $EXT_IF #Our internel nets get priority
#over the server
1:130 206.124.146.177 $EXT_IF tcp - 873 #Throttle rsync traffic to the
#Shorewall Mirrors.
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting></para>
</blockquote>
</section>
<section id="Wireless">
<title>Wireless Gateway DomU Configuration</title>
<para>The Shorewall configuration in the 'wireless' DomU is very simple.
It's sole purpose is to protect the local network from the Wireless net
by restricting wireless access to clients that have established an
<ulink url="OPENVPN.html">OpenVPN</ulink> Bridged connection. This
configuration illustrates that you can use any system on your internal
LAN as a wireless gateway -- it doesn't have to be your main firewall
(and it doesn't have to run in a Xen domain either and it doesn't even
have to run Linux). Our wireless gateway runs a DHCP server that assigns
wireless hosts an IP address in 192.168.3.0/24 -- The OpenVPN server
running on the gateway assigns its clients an IP address in
192.168.1.0/24 so, thanks to bridging, these clients appear to be
physically attached to the LAN). That allows our two laptops to have the
same IP address in 192.168.1.0/24 regardless of whether they are
connected to the LAN directly or are connected via the wireless
network.</para>
<graphic align="center" fileref="images/Xen6.png" />
<para>The 'tap0' device used by OpenVPN is bridged to eth2 using this
SUSE-specific startup script (see the <ulink url="bridge.html">Shorewall
Bridge Documentation</ulink> for scripts that work on other
distributions):</para>
<blockquote>
<para><filename>/etc/init.d/bridge</filename>:</para>
<programlisting>#!/bin/sh
#
# The Shoreline Firewall (Shorewall) Packet Filtering Firewall - V3.0
#
# This program is under GPL [http://www.gnu.org/copyleft/gpl.htm]
#
# (c) 1999,2000,2001,2002,2003,2004,2005 - Tom Eastep (teastep@shorewall.net)
#
# On most distributions, this file should be called /etc/init.d/shorewall.
#
# Complete documentation is available at http://shorewall.net
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of Version 2 of the GNU General Public License
# as published by the Free Software Foundation.
#
# 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 details.
#
# 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
#
# If an error occurs while starting or restarting the firewall, the
# firewall is automatically stopped.
#
# Commands are:
#
# bridge start Starts the bridge
# bridge restart Restarts the bridge
# bridge reload Restarts the bridge
# bridge stop Stops the bridge
# bridge status Displays bridge status
#
# chkconfig: 2345 4 99
# description: Packet filtering firewall
### BEGIN INIT INFO
# Provides: bridge
# Required-Start: boot.udev
# Required-Stop:
# Default-Start: 2 3 5
# Default-Stop: 0 1 6
# Description: starts and stops the bridge
### END INIT INFO
################################################################################
# Interfaces to be bridged -- may be listed by device name or by MAC address
#
INTERFACES="eth2"
#
# Tap Devices
#
TAPS="tap0"
################################################################################
# Give Usage Information #
################################################################################
usage() {
echo "Usage: $0 start|stop|reload|restart|status"
exit 1
}
#################################################################################
# Find the interface with the passed MAC address
#################################################################################
find_interface_by_mac() {
local mac=$1 first second rest dev
/sbin/ip link ls | while read first second rest; do
case $first in
*:)
dev=$second
;;
*)
if [ "$second" = $mac ]; then
echo ${dev%:}
return
fi
esac
done
}
################################################################################
# Convert MAC addresses to interface names
################################################################################
get_interfaces() {
local interfaces= interface
for interface in $INTERFACES; do
case $interface in
*:*:*)
interface=$(find_interface_by_mac $interface)
[ -n "$interface" ] || echo "WARNING: Can't find an interface with MAC address $mac"
;;
esac
interfaces="$interfaces $interface"
done
INTERFACES="$interfaces"
}
################################################################################
# Configure the Bridge -- IP configuration is left to the SUSE network scripts
################################################################################
do_start()
{
local interface
get_interfaces
for interface in $TAPS; do
/usr/sbin/openvpn --mktun --dev $interface
done
/sbin/brctl addbr br0
for interface in $INTERFACES $TAPS; do
/sbin/ip link set $interface up
/sbin/brctl addif br0 $interface
done
}
################################################################################
# Stop the Bridge
################################################################################
do_stop()
{
local interface
get_interfaces
for interface in $INTERFACES $TAPS; do
/sbin/brctl delif br0 $interface
/sbin/ip link set $interface down
done
/sbin/ip link set br0 down
/sbin/brctl delbr br0
for interface in $TAPS; do
/usr/sbin/openvpn --rmtun --dev $interface
done
}
################################################################################
# E X E C U T I O N B E G I N S H E R E #
################################################################################
command="$1"
case "$command" in
start)
do_start
;;
stop)
do_stop
;;
restart|reload)
do_stop
do_start
;;
status)
/sbin/brctl show
;;
*)
usage
;;
esac</programlisting>
<para>As mentioned in the comments in the above script, IP
configuration of the bridge is done through the normal SUSE network
scripts. Here's the config file:</para>
<programlisting>BOOTPROTO='static'
BROADCAST=''
IPADDR='192.168.1.7'
MTU=''
NAME='Ethernet Network Card'
NETMASK='255.255.255.0'
NETWORK=''
REMOTE_IPADDR=''
STARTMODE='auto'
USERCONTROL='no'
_nm_name='br0'</programlisting>
<para>Since there is no requirement to restrict connections through
the bridge, I set BRIDGING=No in
<filename>/etc/shorewall/shorewall.conf</filename>.</para>
<para><filename>/etc/shorewall/zones</filename>:</para>
<programlisting>#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
fw firewall
Wifi ipv4
loc ipv4
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/interfaces</filename>:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
Wifi eth4 192.168.3.255 dhcp,maclist
loc br0 192.168.1.255 dhcp,routeback
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE
</programlisting>
<para><filename>/etc/shorewall/policy</filename> (again, note the use
of an ACCEPT all-&gt;all policy):</para>
<programlisting>#SOURCE DEST POLICY LOG LIMIT:BURST
# LEVEL
Wifi all REJECT info
all all ACCEPT
#LAST LINE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/tunnels</filename>:</para>
<programlisting>#TYPE ZONE GATEWAY GATEWAY
# ZONE
openvpnserver Wifi 192.168.3.0/24
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
<para><filename>/etc/shorewall/maclist (Note that this system runs
Shorewall 3.2 so there is an additional 'TARGET'
column)</filename>:</para>
<programlisting>#TARGET INTERFACE MAC IP ADDRESSES (Optional)
ACCEPT eth4 00:04:5a:0e:85:b9 #WAP11
ACCEPT eth4 00:06:25:45:33:3c #WET11
ACCEPT eth4 00:0b:cd:53:cc:97 192.168.3.8 #TIPPER
ACCEPT eth4 00:0f:66:ef:b6:f6 192.168.3.8 #TIPPER1
ACCEPT eth4 00:12:79:3d:fe:2e 192.168.3.6 #Work Laptop
ACCEPT eth4 - 192.168.3.254 #Broadcast/Multicast from us
DROP:info eth4 - 192.168.3.0/24
DROP:info eth4 - 169.254.0.0/16 #Stop autoconfigured hosts.
#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
<para>The routing table on the wireless gateway is as follows:</para>
<blockquote>
<programlisting>192.168.3.0/24 dev eth4 proto kernel scope link src 192.168.3.254
192.168.1.0/24 dev br0 proto kernel scope link src 192.168.1.7
169.254.0.0/16 dev eth4 scope link
127.0.0.0/8 dev lo scope link
default via 192.168.1.254 dev br0</programlisting>
</blockquote>
<para>The route to 169.254.0.0/16 is automatically generated by the
SUSE network scripts so I include that network in the
<filename>/etc/shorewall/maclist</filename> file for
completeness.</para>
<para><filename>/etc/shorewall/rules</filename>:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST SOURCE ORIGINAL RATE USER/
# PORT PORT(S) DEST LIMIT GROUP
#SECTION ESTABLISHED
#SECTION RELATED
SECTION NEW
ACCEPT Wifi loc:192.168.1.5 udp 123 #Allow NTP before OpenVPN is up.
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
</blockquote>
<para>Here is the configuration of OpenVPN on this system:</para>
<blockquote>
<para><filename>/etc/openvpn/server-bridge</filename> (Note that I
prefer to push two /1 routes rather than to use the <emphasis
role="bold">redirect-gateway</emphasis> directive on the client
systems; I find that <emphasis role="bold">redirect-gateway</emphasis>
occasionally leaves a client system with <emphasis
role="bold">no</emphasis> default gateway):</para>
<programlisting>dev tap0
local 192.168.3.254
server-bridge 192.168.1.7 255.255.255.0 192.168.1.64 192.168.1.71
client-to-client
dh dh1024.pem
ca /etc/certs/cacert.pem
crl-verify /etc/certs/crl.pem
cert /etc/certs/wireless.pem
key /etc/certs/wireless_key.pem
port 1194
comp-lzo
user nobody
group nogroup
keepalive 15 45
ping-timer-rem
persist-tun
persist-key
client-config-dir /etc/openvpn/bridge-clients
ccd-exclusive
verb 3
push "route 0.0.0.0 128.0.0.0 192.168.1.254"
push "route 128.0.0.0 128.0.0.0 192.168.1.254"</programlisting>
<para><filename>/etc/bridge-clients/tipper.shorewall.net</filename>
(used to assign a fixed IP address to clients -- there are other
similar files in this directory):</para>
<programlisting>ifconfig-push 192.168.1.8 255.255.255.0</programlisting>
</blockquote>
<para>Finally, here's a copy of the OpenVPN configuration file on
tipper, one of the laptops:</para>
<blockquote>
<programlisting>dev tap
remote 192.168.3.254
tls-remote wireless.shorewall.net
client
tls-client
explicit-exit-notify
ca /etc/certs/cacert.pem
cert /etc/certs/tipper.pem
key /etc/certs/tipper_key.pem
port 1194
comp-lzo
ping 15
ping-restart 45
ping-timer-rem
persist-tun
persist-key
mute-replay-warnings
verb 3</programlisting>
</blockquote>
</section>
</section>
</article>
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