[squid-users] questions setting up transparent proxy

[John Ratliff]

On 1/3/2018 9:05 PM, Amos Jeffries wrote:
 > On 04/01/18 14:09, John Ratliff wrote:
 >> On 1/3/2018 3:26 PM, Antony Stone wrote:
 >>> On Wednesday 03 January 2018 at 21:06:42, John Ratliff wrote:
 >>>
 >>>> When I try to setup squid as a transparent proxy, I never get any
 >>>> response from Squid.
 >>>
 >>>> When I try a wget request from a server that is being redirected
 >>>
 >>> How (and more importantly, where) are you doing the redirect?
 >>>
 >>>> Both machines are behind the same firewall. I used
 >>>> iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to
 >>>> 10.77.9.120:3128
 >>>
 >>> If that firewall is not on the machine running Squid, then that's
 >>> your problem.
 >>>
 >>>> Traffic flows to the server running squid. I can verify this with
 >>>> tcpdump. The packets are making it from wget to the server. I just
 >>>> don't
 >>>> know what happens after that.
 >>>
 >>> https://wiki.squid-cache.org/ConfigExamples/Intercept/LinuxRedirect
 >>>
 >>> "NOTE: This configuration is given for use *on the squid box*. This
 >>> is required
 >>> to perform intercept accurately and securely. To intercept from a
 >>> gateway
 >>> machine and direct traffic at a *separate squid box* use policy
 >>> routing."
 >>>
 >>> 
https://wiki.squid-cache.org/ConfigExamples/Intercept/IptablesPolicyRoute
 >>>
 >>>
 >>>
 >>> Antony.
 >>>
 >>
 >> Thanks. I put squid on the firewall itself. It works for http, but not
 >> for https. I get errors with curl and wget.
 >>
 >> $ curl https://debian.org
 >> curl: (35) error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown
 >> protocol
 >>
 >> $ wget https://debian.org
 >> --2018-01-03 20:02:45--  https://debian.org/
 >> Resolving debian.org (debian.org)... 5.153.231.4, 128.31.0.62,
 >> 130.89.148.14, ...
 >> Connecting to debian.org (debian.org)|5.153.231.4|:443... connected.
 >> GnuTLS: An unexpected TLS packet was received.
 >> Unable to establish SSL connection.
 >>
 >> I made some config changes:
 >>
 >> http_port 3128 intercept
 >> http_port 3129 intercept ssl-bump generate-host-certificates=on
 >> cert=/etc/squid/squid.pem
 >
 > That should be:
 >
 >   https_port 3129 intercept ssl-bump generate-host-certificates=on \
 >     cert=/etc/squid/squid.pem
 >
 > Note the 's' in https_port.
Thanks. This was the issue.

 >
 >
 >>
 >> sslcrtd_program /usr/lib/squid/ssl_crtd -s /var/lib/ssl_db -M 4MB
 >>
 >> ssl_bump bump all
I changed it to peek and splice.

 >
 >
 > This instructs Squid to bump before even receiving the client TLS
 > handshake - ie. generate a server certificate with zero details to work
 > with about what the client wants.
 > That leads to a LOT of problems and security issues. Please do not do 
that.
 >
 > See <https://wiki.squid-cache.org/Features/SslPeekAndSplice> for better
 > config examples.
 >
 >
 >>
 >> Here are my PREROUTING nat table rules.
 >>
 >> REDIRECT tcp  --  10.77.9.0/24 anywhere tcp dpt:http redir ports 3128
 >> REDIRECT tcp  --  10.77.9.0/24 anywhere tcp dpt:https redir ports 3129
 >>
 >> And in the INPUT chain of the filter table:
 >>
 >> ACCEPT tcp  --  10.77.9.0/24 anywhere tcp dpt:3128
 >> ACCEPT tcp  --  10.77.9.0/24 anywhere tcp dpt:3129
 >>
 >> The server I am on has IP 10.77.9.102.
 >>
 >
 >
 > You appear to be missing the MASQUERADE rule to send packets back to the
 > client.
I have SNAT rules instead. There are many IPs on this firewall.

 >
 > Also the mangle table (*not* filter) rules are important to block
 > external traffic directly to those Squid ports without interfering with
 > the NAT operations.
I didn't post these rules, but I made them. Thanks.


Thanks.