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.

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 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.

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 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. In some cases (when running an LTSP server on the Shorewall system), you might want to transparently proxy web connections that originate on the firewall itself. This requires care to ensure that Squid's own web connections are not proxied. First, determine the user id that Squid is running under: gateway:/etc/shorewall# ps aux | fgrep -i squid | fgrep -v fgrep root 10085 0.0 0.0 23864 700 ? Ss Apr22 0:00 /usr/sbin/squid -D -YC proxy 10088 0.0 0.9 40512 19192 ? S Apr22 10:58 (squid) -D -YC gateway:/etc/shorewall# In this case, the proxy process (squid) is running under the proxy user Id. We add these rules: #ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL RATE USER/ # PORT(S) DEST LIMIT GROUP ACCEPT $FW net tcp www REDIRECT $FW 3128 tcp www - - - !proxy

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,notrack 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 In /etc/shorewall/interfaces : #ZONE INTERFACE BROADCAST OPTIONS loc eth1 detect routeback,routefilter=0,logmartians=0 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 the dmz is connected through eth2 and that your local lan interfaces through eth1 Add this entry to your /etc/shorewall/providers file. #NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS Squid 1 202 - eth2 192.0.2.177 loose,notrack In /etc/shorewall/tcrules add: #MARK SOURCE DEST PROTO DEST # PORT(S) 202:P eth1 0.0.0.0/0 tcp 80 In /etc/shorewall/interfaces : #ZONE INTERFACE BROADCAST OPTIONS loc eth2 detect routefilter=0,logmartians=0 On 172.0.2.177, arrange for the following command to be executed after networking has come up iptables -t nat -A PREROUTING -i eth0 ! -d 192.0.2.177 -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

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 /etc/shorewall/rules: #ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT loc $FW tcp 8080 ACCEPT $FW net tcp 80,443

Shorewall 4.5.4 contains support for TPROXY. TPROXY differs from REDIRECT in that it does not modify the IP header and requires Squid 3 or later. Because the IP header stays intact, TPROXY requires policy routing to direct the packets to the proxy server running on the firewall. This approach requires TPROXY support in your kernel and iptables and Squid 3. See http://wiki.squid-cache.org/Features/Tproxy4. Support for the TPROXY action in shorewall-tcrules(5) and the local option in shorewall-providers(5) has been available since Shoreall 4.4.7. That support required additional rules to be added in the 'start' extention script to make it work reliably. The following configuration works with Squid running on the firewall itself (assume that Squid is listening on port 3129 for TPROXY connections). /etc/shorewall/interfaces: #ZONE INTERFACE BROADCAST OPTIONS - lo - - /etc/shorewall/providers: #NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS COPY Tproxy 1 - - lo - tproxy Notice that the MARK, DUPLICATE and GATEWAY columns are empty and that the only option is tproxy. /etc/shorewall/tcrules (assume loc interface is eth1 and net interface is eth0): FORMAT 2 #MARK SOURCE DEST PROTO DEST SOURCE # PORT(S) PORT(S) DIVERT eth0 0.0.0.0/0 tcp - 80 TPROXY(3129) eth1 0.0.0.0/0 tcp 80 The DIVERT rules are used to avoid unnecessary invocation of TPROXY for request packets after the connection is established and to direct response packets back to Squid3. If you run a web server on the Shorewall system that also listens on port 80, then you need to exclude it from TPROXY. Suppose that your web server listens on 192.0.2.144; then: FORMAT 2 #MARK SOURCE DEST PROTO DEST SOURCE # PORT(S) PORT(S) DIVERT eth0 0.0.0.0/0 tcp - 80 TPROXY(3129) eth1:!192.0.2.144 0.0.0.0/0 tcp 80 /etc/shorewall/rules: #ACTION SOURCE DEST PROTO DEST PORT(S) ACCEPT loc $FW tcp 80 ACCEPT $FW net tcp 80 /etc/squid3/squid.conf: ... http_port 3129 tproxy ... If you use TPROXY with both IPv4 and IPv6, then both your local hosts and the gateway must have the same DNS view. If a client resolves a website URL to an IPv6 address and the server can only resolve to an IPv4 address, then Squid will attempt to connect to the IPv4 address using the local client's IPv6 address. That clearly doesn't work.