On 4/04/2013 3:16 a.m., Ewan Sadie wrote:
I am new to iptables so I tried the following.
I changed the listning port on the proxy to 3127, so that I do not need to change the DNAT on the router.
The router does a DNAT to 3128.
What you have done:
Router receives a packet saying:
client 192.168.0.2 connnect to website 1.2.3.4:80
router NAT removes 1.2.3.4:80 and adds 192.168.0.1:3128
Squid box receives a packet saying:
client 192.168.0.1 connect to website 192.168.0.1:3128
Squid box NAT removes 192.168.0.1:3128 and adds 192.168.0.1:3127
Squid receives packet saying:
client 192.168.0.1 connect to website 192.168.0.1:3127
the box NAT system informs Squid the packet destination was
originally 192.168.0.1:3128
... there is a result. NAT is working perfectly fine *on the Squid
box*. So failure warnings do not appear.
But where does Squid connect?
The HTTP Host: header cannot be trusted much in interception mode
(http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-0801). Squid-3.2
and later will verify that 192.168.0.2:3128 IP address NAT delivered
belongs to the Host: header domain before allowing the Host: header to
be used. When it fails (as it will fail 100% on your system) Squid will
be transparent and pass the request on t the same place the cleint was
connection.
On your system Squid is transparently relaying the intercepted traffic
to the web server it is being told exists at 192.168.0.1:3128.
Routers need to *route* the port 80 traffic to the Squid box *without*
using NAT.
Amos
I then ran the following command on the Squid server, iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 3128 -j REDIRECT --to-port 3127
I now do not see the forward loop errors any more but I do get TCP_MISS/503
I can still browse vie the proxy by connecting to port 8080 so I know there is no rules blocking me.
The fact the I get results in the access.log indicates to me that the redirection is happening.
-----Original Message-----
From: Ewan Sadie
Hi All
Did the handling of intercept change since Squid 3.2.x?
Based on this article http://myconfigure.blogspot.com/2013/03/transparent-squid-332-on-ubuntu-1210.html, it seems that you have to do a rediect on the Squid box itself as well as on the router.
Is this the case? I do not want to over complicate the setup with an aditional firewall as well.
Switch "as well as" for "istead of" and you will have the right idea.
Amos
