[tproxy] Squid with tproxy extra brief FAQ - take 2

Ming-Ching Tiew mingching.tiew at redtone.com
Wed Feb 27 03:31:11 CET 2008

1. There are at least 3 different versions of tproxy kernel patches.

    Each tproxy kernel patch is quite strongly tied to a kernel version,

   (A) Version Tproxy2
   For kernel 2.6.18
   URL: http://www.balabit.hu/downloads/files/tproxy/obsolete/

   (B) Version Tproxy 4.0.x
    For kernel 2.6.22
    URL: http://www.balabit.hu/downloads/files/tproxy/

   (C) Version Tproxy-4.1.0
    For kernel 2.6.25
    URL: The "official website" is for kernel <=2.6.24

     but the actual version of tproxy 4.1 for 2.6.25 is here:

    The kernel patch might work with nearby kernel versions, for example,
    tproxy2 might work with kernel 2.6.19; however it will not work
    will kernel 2.6.22 ( unless you port it ).

2. Do not confuse tproxy kernel patch mentioned above with
    squid user-space patches.

    So far the Squid ( 3.0 and 2.6 ) is only supporting on tproxy2 - the
    userspace code is integrated.

    If you managed to compile Squid without changing the source,
    perhaps with only minor changes in header files, meaning you are
    likely either did not successfully link in tproxy support or at best it
    is using tproxy2, and it will not work with tproxy-4.0.x and
    tproxy-4.1.0 kernel counterpart.

    However, if you patch the squid source, you should be able
    to get squid to work with tproxy-4.0.x and tproxy-4.1.0.

    You can look through the archive of this maillist to look at how
    to port squid versions to support tproxy-4.0.x and tproxy-4.1.0.
    Most of the patches floating around are not fully satisfactory,
    but it could work, at least; but perhaps it will require you to have
    some programming knowledge.

    Here maybe a good start :-

3. All the tproxy kernel patches are not compatible with one another.
    Each requires it's own way of setup and usage. So before doing
    anything, check if you have gotten the correct info/tproxy version/patches.

    These are some of the info :-

     (A) Version Tproxy2
     The Squid documentation recommends this :-

           ebtables -t broute -A BROUTING -p ipv4 --ip-protocol tcp \
                 --ip-destination-port 80 -j redirect --redirect-target ACCEPT

      This rule will "broute" bridge traffic from br0 to netfilter.

      The iptables rule will bring http traffic into local process  :-

             iptables -t tproxy -A PREROUTING -i br0 -p tcp --dport 80 \
              -j TPROXY --on-port 3128

      To get SNAT working for tproxy2, there is a need for double NAT,
       and here was the discussion and patch :-


      (B) Version tproxy-4.0.x
      Requires additional patches for SNAT and FWMARK.
      Some hurdles with bridge.

      Bridge problem is to do with packets must be marked PACKET_HOST when
      heading for br0 as discussed in this tproxy maillist. There have been
      people saying they will post the patch for it  but yet to date, there is none.

     This problem can be worked around by brouting the traffic into
     the real devices instead of br0 :-

      ebtables -t broute -A BROUTING -i $INSIDE_DEV -p ipv4 \
              --ip-protocol tcp --ip-destination-port 80 \
               -j redirect --redirect-target DROP
      ebtables -t broute -A BROUTING -i $OUTSIDE_DEV -p ipv4 \
        --ip-protocol tcp --ip-source-port 80 \
         -j redirect --redirect-target DROP

      Please note for real interfaces, it's  redirect-target DROP and
      not redirect-target ACCEPT, while doing it on br0, it's
      redirect-target ACCEPT !

      Remember to adjust your iptables rule accordingly since now
      packets entering and leaving real  interfaces instead of br0.

      Example :-

       iptables -t tproxy -A PREROUTING -i $INSIDE_DEV \
             -p tcp --dport 80 -j TPROXY --on-port 3128

      For tproxy-4.0.3 remember to apply the additional kernel patches
      mentioned in this maillist or else the kernel will panic accessing
      null pointer.

      (C) Version tproxy-4.1.0
      The ebtables/bridge notes above is equally applicable. However 
      the iptables rules are totally different.

      Something like this will be required :-

           iptables -t mangle -A PREROUTING -p tcp --dport 80 -j TPROXY \
                  --tproxy-mark 0x1/0x1 -on-port 3128
            iptables -t mangle -N DIVERT
            iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
            iptables -t mangle -A DIVERT -j MARK --set-mark 1
            iptables -t mangle -A DIVERT -j ACCEPT

            ip rule add fwmark 1 lookup 100
            ip route add local dev lo table 100

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