This is my first thread and hope someone will provide me a solution and the reason

Im using BT4 on vmware and i am trying to sniff my local network which is connected to a Juniper L3 switch. And i am facing these problems

1. I can sniff successfully to the switch and my host system in all login attempts but when i try to sniff the other systems, the connection fails or the internet dont respond at all at that system or it does not do sniffing.

2. And after that when i close ettercap or stop sniffing the target disconnects to internet as well, if i start sniffing again the internet works again.