I have a router Cisco 2821 and a ADSL modem. The ADSL modem is connected to ADSL cabled to the ISP, and also is connected directly to the GigaEthernet 0/1 port of the router. The GigaEthernet 0/0 on the router cisco is connected directly to my LAN on a Cisco switch's port. A route to the internet (0.0.0.0 mask 0.0.0.0) via the ADSL modem's local IP address is established. I manage accessing from computers in my LAN to the internet through extend access-list on my Cisco router. Now I want to block file transfer over network applications such as skype, yahoo ... from some local IP address, could you show me how to do? Many many thanks to you, pros! Nice day to you all!