You would like to block all network traffic using iptables firewall under Debian GNU/Linux. This will block all incoming and outgoing traffic including Internet aka ADSL/ppp0 and it is highly recommend. The logic is block everything and allow only required traffic. This can be done with four simple commands:
# iptable -F # iptables -P INPUT DROP # iptables -P OUTPUT DROP # iptables -P FORWARD DROP
Please do not enter above command over remote ssh login session.