Hi Rene,
It appears there are lot of user's with similar problem with bigpond's firmware on SIEMENS SpeedStream 6520 router.
Since I don't have access to that router physically, I found this thread (
http://forums.whirlpool.net.au/forum...fm/317072.html) and to change settings (
http://forums.whirlpool.net.au/forum...16588#r4716588)
In summary they are saying if you update your firmware to the latest one you can change your settings. (
http://forums.whirlpool.net.au/forum...64093#r7664093)
Hopefully this is helpful to you.