# Using Shorewall with Squid

Tom
Eastep
2003-2008
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 .

This page covers Shorewall configuration to use with Squid running as a Transparent Proxy or as a Manual Proxy.

This article applies to Shorewall 4.0 and later. If you are running a version of Shorewall earlier than Shorewall 4.0.0 then please see the documentation for that release.

## Squid as a Transparent (Interception) Proxy

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:

  1. 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

  2. Allowing HTTP access to that ACL.

     Example:

         http_access allow my_networks

  See your distribution's Squid documentation 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.

## Configurations

Three different configurations are covered:

- Squid (transparent) Running on the Firewall
- Squid (transparent) Running in the local Network
- Squid (transparent) Running in a DMZ

### Squid (transparent) 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     ORIGINAL
    #                                                       PORT(S)    DEST
    ACCEPT    $FW        net      tcp      www
    REDIRECT  loc        3128     tcp      www              -          !206.124.146.177

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

People frequently ask How can I exclude certain internal systems from using the proxy? I want to allow those systems to go directly to the net.

Suppose that you want to exclude 192.168.1.5 and 192.168.1.33 from the proxy. Your rules would then be:

    #ACTION   SOURCE     DEST     PROTO    DEST PORT(S)     SOURCE     ORIGINAL
    #                                                       PORT(S)    DEST
    ACCEPT    $FW        net      tcp      www
    REDIRECT  loc:!192.168.1.5,192.168.1.33\
                         3128     tcp      www              -          !206.124.146.177,130.252.100.0/24
    ACCEPT    loc        net      tcp      www

The last rule may be omitted if your loc->net policy is ACCEPT.

### Squid (transparent) 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.

1. 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

2. In `/etc/shorewall/tcrules` add:

       #MARK    SOURCE              DEST        PROTO    DEST
       #                                                 PORT(S)
       202:P    eth1:!192.168.1.3   0.0.0.0/0   tcp      80

3. In ``/etc/shorewall/interfaces`` :

       #ZONE   INTERFACE    BROADCAST    OPTIONS
       loc     eth1         detect       routeback

4. 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

### Squid (transparent) Running in the DMZ

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

## Squid as a Manual Proxy

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

### 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