Using Shorewall with Squid

This page covers Shorewall configuration to use with Squid running as a Transparent Proxy. If you are running Shorewall 1.3, please see this documentation.

Caution     Please observe the following general requirements:

    In all cases, Squid should be configured to run as a transparent proxy as described at http://www.tldp.org/HOWTO/mini/TransparentProxy-4.html.

     The following instructions mention the files /etc/shorewall/start and /etc/shorewall/init -- if you don't have those files, siimply create them.

    When the Squid server is in the DMZ zone or in the local zone, that zone must be defined ONLY by its interface -- no /etc/shorewall/hosts file entries. That is because the packets being routed to the Squid server still have their original destination IP addresses.

    You must have iptables installed on your Squid server.

    You must have NAT and MANGLE enabled in your /etc/shorewall/conf file

        NAT_ENABLED=Yes
        MANGLE_ENABLED=Yes

Three different configurations are covered:
  1. Squid running on the Firewall.
  2. Squid running in the local network
  3. Squid running in the DMZ

Squid Running on the Firewall

You want to redirect all local www connection requests EXCEPT those to your own http server (206.124.146.177) to a Squid transparent proxy running on the firewall and listening on port 3128. Squid will of course require access to remote web servers.

In /etc/shorewall/rules:

ACTION SOURCE DEST PROTO DEST
PORT(S)		 SOURCE
PORT(S)		 ORIGINAL
DEST
REDIRECT loc 3128 tcp www -
 !206.124.146.177
ACCEPT fw net tcp www


Squid Running in the local network

You want to redirect all local www connection requests to a Squid transparent proxy running in your local zone at 192.168.1.3 and listening on port 3128. Your local interface is eth1. There may also be a web server running on 192.168.1.3. It is assumed that web access is already enabled from the local zone to the internet.

WARNING: This setup may conflict with other aspects of your gateway including but not limited to traffic shaping and route redirection. For that reason, I don't recommend it.

echo 202 www.out >> /etc/iproute2/rt_tables
if [ -z "`ip rule list | grep www.out`" ] ; then
	ip rule add fwmark 202 table www.out
	ip route add default via 192.168.1.3 dev eth1 table www.out
	ip route flush cache
	echo 0 > /proc/sys/net/ipv4/conf/eth1/send_redirects
fi
iptables -t mangle -A PREROUTING -i eth1 -s ! 192.168.1.3 -p tcp --dport 80 -j MARK --set-mark 202
If you are running RedHat on the server, you can simply execute the following commands after you have typed the iptables command above:
iptables-save > /etc/sysconfig/iptables
chkconfig --level 35 iptables start

Squid Running in the DMZ (This is what I do)

You have a single Linux system in your DMZ with IP address 192.0.2.177. You want to run both a web server and Squid on that system. Your DMZ interface is eth1 and your local interface is eth2.
echo 202 www.out >> /etc/iproute2/rt_tables
if [ -z "`ip rule list | grep www.out`" ] ; then
	ip rule add fwmark 202 table www.out
	ip route add default via 192.0.2.177 dev eth1 table www.out
	ip route flush cache
fi
	iptables -t mangle -A PREROUTING -i eth2 -p tcp --dport 80 -j MARK --set-mark 202
B) Set MARK_IN_FORWARD_CHAIN=No in /etc/shorewall/shorewall.conf and add the following entry in /etc/shorewall/tcrules:
MARK
 SOURCE
 DESTINATION
 PROTOCOL
 PORT
 CLIENT PORT
202
 eth2
 0.0.0.0/0
 tcp
 80
 -
C) Run Shorewall 1.3.14 or later and add the following entry in /etc/shorewall/tcrules:
MARK
 SOURCE
 DESTINATION
 PROTOCOL
 PORT
 CLIENT PORT
202:P
 eth2
 0.0.0.0/0
 tcp
 80
 -
ACTION
 SOURCE
 DEST
 PROTO
 DEST
PORT(S)
 CLIENT
PORT(2)
 ORIGINAL
DEST
ACCEPT
 loc
 dmz
 tcp
 80

ACCEPT
 dmz
 net
 tcp
 80


If you are running RedHat on the server, you can simply execute the following commands after you have typed the iptables command above:
iptables-save > /etc/sysconfig/iptables
chkconfig --level 35 iptables start

Updated 4/7/2003 - Tom Eastep

Copyright © 2003 Thomas M. Eastep.