I have spent some hours with Hell4You debugging an issue with p300 connectivity on his network. The result of the issues were that browsing and chatting sometimes worked, sometimes it didn’t. By looking at the p300-generated hostfinder webpage and debugging around with the Eclipse debugger we were able to track it down: Some of his hardware / software is duplicating UDP packets and using its own IP as the source IP of the duplicated packet. Really really weird stuff. This resulted in connectivity sometimes not working because the wrong IP was used by p300.
The latest p300 version that will come in some weeks will fix this issue: It will always be checked with HTTP if some ip:port is really running p300. If you experience the same problem as described here, I can send it earlier
For the record, he is using a 3com OfficeConnect and a SpeedTouch 780wl.
Lesson learned? Never trust UDP!