bt3 shutsdown network for all but me?

[aftermathzx]

so there is 3 computers in my house
though whenever i run bt3 on one of them all seems well and i can run the internet through bt3 but on all the other computers the internet stops working.
when i get out of bt3 the internet runs fine again

im trying to monitor my network using:
urlsnarf -i eth0
ettercap -T -q -p -M ARP // //
driftnet -a -d /root/images -s -p -i eth0

is there something in my code that shuts down the internet for everyone but me?
(im new to bt3 btw)
thanks

[gromeo]

yes, you did not enable forwarding on your interface.

[aftermathzx]

thank you, now how do i enable forwarding on my interface?