[lug] Transparent proxy on localhost

[George Sexton]

I've seen this before. Localhost doesn't traverse the pre-routing chain. 
In my case, I was running tomcat on port 8080 and redirecting to port 
80. Same problem.

Michael Hirsch wrote:
> I'm trying to set up a transparent proxy on localhost.  (I'm trying to
> filter my kids' web browsing.)  I have the proxy all setup and
> working, but I can't figure out how to get it to happen transparently.
>  Here's what I've tried:
> 
> modprobe iptable_nat
> echo 1 > /proc/sys/net/ipv4/ip_forward
> 
> #Clean things out:
> iptables -F
> iptables -X
> iptables -t nat -F
> iptables -t nat -X
> #setup up transparent proxy
> iptables -t nat -A PREROUTING -p tcp --dport 80 -j LOG
> iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-ports 8080
> 
> This is what googling gives me as the proper command, but it doesn't
> do anything.  Actually, it does.  If I connect from another computer I
> can see the LOG command get hit, but if I run the browser on
> localhost, it does nothing.
> 
> I'm guessing that I need to do something special to get it to work on
> the localhost rather than an external connection.  I tried:
> 
> iptables -t nat -i lo -A PREROUTING -p tcp --dport 80 -j LOG
> iptables -t nat -i lo -A PREROUTING -p tcp --dport 80 -j REDIRECT
> --to-ports 8080
> 
> but there's no change in behavior.  The web connection is unfiltered.
> 
> What am I doing wrong?
> 
> Thanks,
> 
> Michael
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-- 
George Sexton
MH Software, Inc.
Voice: +1 303 438 9585
URL:   http://www.mhsoftware.com/