Copyright © 2003-2007 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 ”.
2007/07/19
Table of Contents
This page covers Shorewall configuration to use with Squid running as a Transparent Proxy or as a Manual Proxy.
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.
This section gives instructions for transparent proxying of HTTP. HTTPS (normally TCP port 443) cannot be proxied transparently (stop and think about it for a minute; if HTTPS could be transparently proxied, then how secure would it be?).
Please observe the following general requirements:
In all cases, Squid should be configured to run as a transparent proxy as described at http://wiki.squid-cache.org/SquidFaq/InterceptionProxy.
The bottom line of that article is that if you are running Squid 2.6 or later, then you simply need to add the word transparent to your http_port specification:
http_port 3128 transparent
In earlier Squid versions, you need to set several options:
http_port 3128 httpd_accel_host virtual httpd_accel_port 80 httpd_accel_with_proxy on httpd_accel_uses_host_header on
Depending on your distribution, other Squid configuration changes may be required. These changes typically consist of:
Adding an ACL that represents the clients on your local network.
Example:
ACL my_networks src 192.168.1.0/24 192.168.2.0/24
Allowing HTTP access to that ACL.
Example:
http_access allow my_networks
See your distribution's Squid documenation and http://www.squid-cache.org/ for details.
It is a good idea to get Squid working as a manual proxy first before you try transparent proxying.
The following instructions mention the file /etc/shorewall/start - if you don't have that file, simply create it.
When the Squid server is 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.
In the instructions below, only TCP Port 80 is opened from the system running Squid to the Internet. If your users require browsing sites that use a port other than 80 (e.g., http://www.domain.tld:8080) then you must open those ports as well.
Three different configurations are covered:
| Squid (transparent) Running on the Firewall |
| Squid (transparent) Running in the local Network |
| Squid (transparent) Running in a DMZ |
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 ORIGINAL # PORT(S) DEST REDIRECT loc 3128 tcp www - !206.124.146.177 ACCEPT $FW net tcp www
There may be a requirement to exclude additional destination hosts or networks from being redirected. For example, you might also want requests destined for 130.252.100.0/24 to not be routed to Squid.
If needed, you may just add the additional hosts/networks to the ORIGINAL DEST column in your REDIRECT rule.
/etc/shorewall/rules:
#ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL # PORT(S) DEST REDIRECT loc 3128 tcp www - !206.124.146.177,130.252.100.0/24
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.
Add this entry to your /etc/shorewall/providers file.
#NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS Squid 1 202 - eth1 192.168.1.3 loose
In /etc/shorewall/start add:
iptables -t mangle -A PREROUTING -i eth1 -s ! 192.168.1.3 -p tcp --dport 80 -j MARK --set-mark 202 In :/etc/shorewall/interfaces
#ZONE INTERFACE BROADCAST OPTIONS
loc eth1 detect routeback On 192.168.1.3, arrange for the following command to be executed after networking has come up
iptables -t nat -A PREROUTING -i eth0 -d ! 192.168.1.3 -p tcp --dport 80 -j REDIRECT --to-ports 3128 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 on You have a single system in your DMZ with IP address 192.0.2.177. You want to run both a web server and Squid on that system.
In /etc/shorewall/rules:
#ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL # PORT(S) DEST DNAT loc dmz:192.0.2.177:3128 tcp 80 - !192.0.2.177
Assume that Squid is running in zone SZ and listening on port SP; all web sites that are to be accessed through Squid are in the “net” zone. Then for each zone Z that needs access to the Squid server.
/etc/shorewall/rules:
#ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT Z SZ tcp SP ACCEPT SZ net tcp 80,443
Example 1. Squid on the firewall listening on port 8080 with access from the “loc” zone:
/etc/shorewall/rules:
#ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT loc $FW tcp 8080 ACCEPT $FW net tcp 80,443