TCP port forwarding with linux iptables NAT, PREROUTING and DNAT example

Lets say that we would like to do port forwarding from our network interface eth0 on port 23  (telnet) to socket 10.0.0.1:23 (ip address:port):
iptables -t nat -I PREROUTING -p tcp -i eth0 –dport 111 -j DNAT –to 10.0.0.1:23
other example:
to do port forward from eth0 on port 456 to 192.168.0.1:788
iptables -t nat -I PREROUTING -p tcp [...]

Drop all outgoing traffic with linux iptables to destination port 80 / http / www

To block all outgoing traffic to the port 80 ( http, www, html ) use command:
iptables -A OUTPUT -p tcp –dport 80 -j DROP
To remove all iptables rules use command:
iptables -F
Sometimes you need to DROP all port 80 ( http, www, html ) traffic except certain IP address. In this case you ca run:
iptables -A [...]

Anonymously browsing internet – linux anonymizer

If your are concerned about your privacy in regards to internet browsing you may try use tor and the privoxy proxy server to hide your true identity while surfing the internet. The setup is very easy and is definitely worth to try.
First install tor and privoxy packages. On debian or ubuntu just simply type:
apt-get install [...]

Listen to the network traffic with tcpdump except ssh

When ssh to remote server tcpdump command floods the screen with packets produces by ssh connection. To exclude ssh connection from tcpdump output we can use command:
# tcpdump -i eth0 not port 22
where eth0 is your network interface.