arch-wiki-md-repo/wiki/_content/english/Upside Down Ternet.md

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This article explains how to create a transparent Squid proxy server using mogrify to flip the images upside down.

## Contents

*   [1 Installation](#Installation)
*   [2 Configuration](#Configuration)
    *   [2.1 Router Setup](#Router_Setup)
*   [3 Starting](#Starting)
*   [4 See also](#See_also)

## Installation

[Install](/index.php/Install "Install") the [squid](https://www.archlinux.org/packages/?name=squid), [apache](https://www.archlinux.org/packages/?name=apache), [wget](https://www.archlinux.org/packages/?name=wget) and [imagemagick](https://www.archlinux.org/packages/?name=imagemagick) packages from the [official repositories](/index.php/Official_repositories "Official repositories").

## Configuration

Create `flip.pl` and place it in your `/usr/local/bin` folder

 `/usr/local/bin/flip.pl` 
```
#!/usr/bin/perl
$|=1;
$count = 0;
$pid = $$;
while (<>) {
       @splitted=split(/ /,$_);
       chomp $_;
       if ($_ =~ /(.*\.jpg)/i) {
               $url = $1;
               system("/usr/bin/wget", "-q", "-O","/srv/http/images/$pid-$count.jpg", "$url");
               system("/usr/bin/mogrify", "-flip","/srv/http/images/$pid-$count.jpg");
               print "http://127.0.0.1/images/$pid-$count.jpg
";
       }
       elsif ($_ =~ /(.*\.gif)/i) {
               $url = $1;
               system("/usr/bin/wget", "-q", "-O","/srv/http/images/$pid-$count.gif", "$url");
               system("/usr/bin/mogrify", "-flip","/srv/http/images/$pid-$count.gif");
               print "http://127.0.0.1/images/$pid-$count.gif
";
       }
       elsif ($_ =~ /(.*\.png)/i) {
               $url = $1;
               system("/usr/bin/wget", "-q", "-O","/srv/http/images/$pid-$count.png", "$url");
               system("/usr/bin/mogrify", "-flip","/srv/http/images/$pid-$count.png");
               print "http://127.0.0.1/images/$pid-$count.png
";
       }
       else {
               print "$splitted[0]
";
       }
       $count++;
}

```

Now we need to modify the permissions so that it's executable

 `# chmod 755 /usr/local/bin/flip.pl` 

Next, while not necessary, does clean up the Squid config file a lot making it easier on the eyes

 `# sed -i "/^#/d;/^ *$/d" /etc/squid/squid.conf` 

Now, edit your squid.conf file and append this to the bottom

 `squid.conf` 
```
url_rewrite_program /usr/local/bin/flip.pl

```

Also find the line for `http_port` and make it now read

 `squid.conf`  `http_port 3128 intercept` 

Finally, we have to create the folders for the images to be flipped in and set their permissions

*The directory where the images are to be stored must be owned by the proxy user.*

```
# mkdir /srv/http/images
# chown proxy:proxy /srv/http/images
# chmod 755 /srv/http/images

```

Finally, add the http user to the proxy group

 `# usermod -aG proxy http` 

Verify that the http user is a member of the proxy group

 `# groups http` 

or

 `# id -Gn http` 

### Router Setup

You will need to edit [iptables](/index.php/Iptables "Iptables") on your router or gateway to redirect http traffic to your proxy.

If you have DD-WRT on your router, this is easily done by going to Administration -> Commands and pasting the following into the box.

```
#!/bin/sh
PROXY_IP=192.168.1.
PROXY_PORT=3128
LAN_IP=`nvram get lan_ipaddr`
LAN_NET=$LAN_IP/`nvram get lan_netmask`
iptables -t nat -A PREROUTING -i br0 -s $LAN_NET -d $LAN_NET -p tcp --dport 80 -j ACCEPT
iptables -t nat -A PREROUTING -i br0 -s ! $PROXY_IP -p tcp --dport 80 -j DNAT --to $PROXY_IP:$PROXY_PORT
iptables -t nat -I POSTROUTING -o br0 -s $LAN_NET -d $PROXY_IP -p tcp -j SNAT --to $LAN_IP
iptables -I FORWARD -i br0 -o br0 -s $LAN_NET -d $PROXY_IP -p tcp --dport $PROXY_PORT -j ACCEPT

```

## Starting

Configure `httpd.service` and `squid.service` to start on boot.

Read [Daemons](/index.php/Daemons "Daemons") for more information.

## See also

*   [Original Upside-Down-Ternet Link](http://www.ex-parrot.com/pete/upside-down-ternet.html)
*   [Ubuntu HowTo](https://help.ubuntu.com/community/Upside-Down-TernetHowTo)
*   [Transparent Proxy with DD-WRT](http://www.dd-wrt.com/wiki/index.php/Squid_Transparent_Proxy)
*   [Upside-Down-Ternet XKCD](http://xkcd.com/341/)