This is for begginners and it requires physical access 1.If you have access to the switches and you can unplug one patch cable from the patch panel or wall and plug it so that both ends of the rj45 are in the switch, you can create a switching loop. The fix for this is to enable STP, on your swithces. 2. Put a *nix machine on the same network, and change the IP of the machine to the IP of the default gateway. The fix for this is to use 802.1x authentication. 3. Inserting a rouge dhcp server on the network, will make it so that depending on network traffic some clients will grab address they can't use. The fix for this is again use 802.1x . 4. On a complicated network use a box with low specs. to arp poison all IP's. The machine won't be able to keep up with the routing and the network will grind to a halt. The fix for this is to again use 802.1x and to use an IDS or IPS. 5. Run Novell Quit using Novell So why don't people use 802.1x on every network? It used to be very tedious and can still be sometimes.