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Special Forums Cybersecurity IPNAT / Transparent proxy loops... Post 30309 by indo1144 on Sunday 20th of October 2002 11:43:02 AM
Old 10-20-2002
IPNAT / Transparent proxy loops...

Hi!

My situation:

I have an OpenBSD firewall/proxy (192.168.0.1), running IPF/IPNAT w/ Squid as transparent proxy. This machine is configured to be gateway to the network.

This works great, all the clients WWW-requests on the internal network are rerouted to the proxyport by this IPNAT-rule:

rdr fxp0 0.0.0.0/0 port 80 -> 192.168.0.1 port 3128

However, I would like to use another machine as a transparent proxy and have run into some problems... The new machine runs Solaris 8 i386 (192.168.0.2) and I have succesfully compiled and configured Squid. I use the same config I used with the "firewall-squid-version".
After changing the IPNAT-rule to:

rdr fxp0 0.0.0.0/0 port 80 -> 192.168.0.2 port 3128

It won't work... I can see a message: Website found, waiting for reply, but figure this is only because DNS-lookup of the website was succesfull. DNS-lookups are punched through the firewall and happen independently from the squid-proxy.

What I figure happened is this:

- A client wants to connect to the internet.
- Request travels to 192.168.0.1 port 80
- Request is redirected to squid on 192.168.0.2 port 3128
- Squid on 192.168.0.2 wants to connect to the internet.
- Squid on 192.168.0.2 connects to 192.168.0.1 port 80
- Squid-request is redirected to squid on 192.168.0.2 port 3128 instead of to internet (because of IPNAT-rule stated above)
- And it continues to loop...

How can I change my IPNAT-rules so that all clients are redirected to 192.168.0.2 port 3128 _AND_ 192.168.0.2 itself is allowed direct access to the internet?
 

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TCPDROP(8)						    BSD System Manager's Manual 						TCPDROP(8)

NAME
tcpdrop -- drop TCP connections SYNOPSIS
tcpdrop local-address local-port foreign-address foreign-port tcpdrop [-l] -a DESCRIPTION
The tcpdrop command may be used to drop TCP connections from the command line. If -a is specified then tcpdrop will attempt to drop all active connections. The -l flag may be given to list the tcpdrop invocation to drop all active connections one at a time. If -a is not specified then only the connection between the given local address local-address, port local-port, and the foreign address foreign-address, port foreign-port, will be dropped. Addresses and ports may be specified by name or numeric value. Both IPv4 and IPv6 address formats are supported. The addresses and ports may be separated by periods or colons instead of spaces. EXIT STATUS
The tcpdrop utility exits 0 on success, and >0 if an error occurs. EXAMPLES
If a connection to httpd(8) is causing congestion on a network link, one can drop the TCP session in charge: # sockstat -c | grep httpd www httpd 16525 3 tcp4 192.168.5.41:80 192.168.5.1:26747 The following command will drop the connection: # tcpdrop 192.168.5.41 80 192.168.5.1 26747 The following command will drop all connections but those to or from port 22, the port used by sshd(8): # tcpdrop -l -a | grep -vw 22 | sh SEE ALSO
netstat(1), sockstat(1) AUTHORS
Markus Friedl <markus@openbsd.org> Juli Mallett <jmallett@FreeBSD.org> BSD
January 30, 2013 BSD
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