[vox-tech] Re: Need to bypass Squid proxy

[Seth Nagao]

How is this transparent proxy hooked up?  Does it also do the routing,
or does another box do this?  Somewhere in your traffic flow it must
be redirected to the transparent proxy (unless you're doing
transparent bridging proxying, but you should be able to remedy that
in a similar fashion).  If it's a Linux router, create an iptables
rule that will not redirect the packets to the transparent proxy if
it's coming from and going to your internal network.  If it's not
Linux, there still should be a way to accomplish the same goal, but
I'm not sure if this list would be useful in that case.

--Seth

On 1/26/06, Micah J. Cowan <micah at cowan.name> wrote:
> On Thu, Jan 26, 2006 at 01:38:54PM -0800, Ehrhart, Jay wrote:
> > I don't think I made what I want to accomplish clear.
> >
> > I am at a county office of Education.  By law all web traffic to the
> > real Internet must be filtered.  I have a Red Hat Linux server running
> > N2H2 web filtering.  It is a transparent proxy.  All traffic goes
> > through the proxy filter and there is no way around it.
> >
> > I have an internal web server that is only for the schools and is not
> > publicly accessible.  The proxy server does its job and sends the
> > traffic out where it dies on the outside of my publicly facing firewall.
> > I want to bypass the proxy with squid or iptables so that the private
> > sites can reach the private web site.
>
> I realize this. The message you're responding to was
> something of a tangent.
>
> So, it is a transparent proxy, and editing your Connection Settings
> won't work. Any changes made must be done at the proxy server, or at a
> routing level.
>
> First off: as things currently stand, does traffic directed at the
> private web server actually get there (though redirected from the proxy
> server)? If not, then you need to make sure that the proxy knows how to
> direct traffic there.
>
> Now, if things are getting to the private web server, but always show
> the IP address from the proxy server, there's a couple options. The
> easiest, if you are able to make the appropriate adjustments at the web
> server, is to comprehend and correctly interpret the HTTP
> X-Forwarded-From (non-standard) header that your proxy should be
> emitting.
>
> Another option is to configure the proxy server to directly forward
> IP packets to the internal web server, virtually unchanged (that is,
> with the original source IP address intact). If you're not using Linux,
> I can't help you there (it may not be possible).
>
> But your best option would be to ensure that the routing tables of the
> machines on your network don't direct intranetwork traffic through the
> proxy. If you're using DHCP, then it's the DHCP server you need to
> configure for this.
>
> HTH,
> Micah
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