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πŸ”— Intercepting traffic with IPFW

πŸ”— Outline

This configuration is for a machine using IPFirewall (IPFW) to NAT intercept traffic into a Squid proxy.

:information_source: NAT configuration will only work when used on the squid box. This is required to perform intercept accurately and securely. To intercept from a gateway machine and direct traffic at a separate squid box use policy routing.

πŸ”— Squid Configuration

First, compile and install Squid. It requires the following options:

./configure --enable-ipfw-transparent

You will need to configure squid to know the IP is being intercepted like so:

http_port 3129 transparent

:warning: In Squid 3.1+ the transparent option has been split. Use β€˜intercept to catch IPFW packets.

http_port 3129 intercept

πŸ”— rc.firewall.local Configuration

# Interface where client requests are coming from

# The IP Squid is listening on for requests. localhost is safest.

# Path to ipfw command

${IPFW} -f flush
${IPFW} add 60000 permit ip from any to any
${IPFW} add 100 fwd ${SQUIDIP},3129 tcp from any to any 80 recv ${IFACE}

πŸ”— Testing

To test if it worked, use the nc utility. Stop squid and from the command line as root type in:

nc -l 3129

Then restart squid and try to navigate to a page.

You should now see an output like this:

<root:freebsd> [/root]
> nc -l 3129
GET / HTTP/1.1
User-Agent: Mozilla/5.0 (compatible; GNotify
Host: example.com
Connection: keep-alive

From there on out, just set your browsers up normally with no proxy server, and you should see the cache fill up and your browsing speed up.

πŸ”— Troubleshooting

πŸ”— On MacOS X 10.6 traffic does not show up in Squid

by Jeffrey j Donovan

You need to edit:

sysctl -w net.inet.ip.scopedroute=0

Previous MacOS X set this to 0 by default. On MacOS X 10.6 it now defaults to 1. Disable this and Squid gets the traffic.

⚠️ Disclaimer: Any example presented here is provided "as-is" with no support
or guarantee of suitability. If you have any further questions about
these examples please email the squid-users mailing list.

Categories: ConfigExample

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