You want to configure a VPN connection to your firewall. It does not work on Android 4.0.4, but the same settings work in 4.1.x and above.
Used in this example: VPN method L2TP IPsec PSK, Samsung GT-P7501, Dell Sonicwall tz 210
According to some googlecode threads, this is a bug which has not been solved for years.
If possible, upgrade to a higher Android version the official way.
Unfortunately, there seems to be no solution which works without rooting the device, because for devices like the Samsung Galaxy Tab 10.1 the latest official Android version is 4.0.4.
So another way would be changing the OS to Cyanogenmod 10.2 or similar, but it is a matter of opinion to use it because it is not supported officially. CM11 also seems not to be supported on this device.
The most effective way for me finally was to root the tablet and change the “racoon” file.
Root the device. KingoApp which runs under Windows is very comfortable for doing this.
Look at the google code thread -> #203. Download the modified racoon file.
Establish an ADB connection to your Android device. If you do not want to install the full Android SDK, there are portable packages available (google “adb tools” etc.).
Open cmd, go to your ADB folder, note the location of your racoon file and execute:
mount -o rw,remount /system
chmod 777 /system/bin/racoon
adb push racoon /system/bin/
su chmod 777 /system/bin/racoon
Then retry your VPN connection.