Re: transparent proxy problem with Linux 2.2.13

Frank Bernard (fb@fbit.de)
Mon, 29 Nov 1999 06:42:28 +0100 (MET)


Hello Robert,

if transparent proxying stops working and the process behind runs, then
probably the rule table has been changed.

If you're alone with the machine, do the following steps :
- Zero out all rule counters (ipchains -Z)
- watch the syslog (e.g. tail -f /var/log/messages)
- make a proxy connection try (e.g. lynx http://www.linuxwall.de)
- after that failed, check the rule counters
(ipchains -L [{input|output}] -v -n)
You see which rules triggered and see what syslog said.
With an analysis of those informations you should be able to isolate the
problem.
Also do a netstat -a -n to seee if the proxy is listening.

For me a "salvation rule" was very helpful :
ipchains -A {input|forward|output} -j DENY -l
as the last rule in each chain logs every unidentified packet passed so
far.

Mit freundlichen Grüßen / king regards

Frank Bernard

Frank Bernard Informationstechnik GmbH
vanity +49 700 FIREWALL (0700 FIREWALL) phone : +49 69 477169
Dipl.-Inform. Frank Bernard fax : +49 69 47885616
Wehrheimerstr. 9 email : fb@fbit.de
60389 Frankfurt www : http://www.fbit.de
Germany http://www.linuxwall.de

On Mon, 29 Nov 1999, Robert Cohen wrote:

>
> I'm having a weird problem with squid 2.2stable5.
> I have it set up as a transparent proxy on a 2.2.13 box.
> I'm using IP chains to redirect port 80 requests to the proxy on port
> 8080.
> I have IP forwarding enabled and am using the following ipchains command
>
> /sbin/ipchains -A input -j REDIRECT 8080 -p tcp -s 203.37.38.0/24 -d
> 0.0.0.0/0 80
>
> The weird thing is that it works fine for about a day then stops
> working.
> No obvious error messages in logs.
> The proxy still works if I contact it explicitly on the proxy port
> rather than using the transparent functionality.
> So networking is still working.
>
> I get an error message back from the squid about "connection lifetime
> exceeded". So the redirection is still working to some extent as the
> request is reaching the squid.
>
> I dont think its a squid problem as such as the same version works fine
> under kernel 2.0.36.
> And when the problem occurs, squid is still working.
>
> So it seems to be some sort of interaction between the IP redirection
> and squid.
> A reboot fixes it, but stopping and restarting squid doesnt.
>
> I'm trying 2.2.14pre9 at the moment to see if it fixes it.
> I notice that the changes for for 2.2.14pre mentions a transproxy fix.
>
> Does anyone know if that transproxy problem is likely to have these
> symptoms.
> Does anyone have any other suggestions as to what could be causing this.
>
> --
> Robert Cohen - Network Administrator
> Apex Internet
> robert@apex.net.au http://www.apex.net.au
> Ph (02) 6247 2000 Fax: (02) 6247 2711
>
> -
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