There are bad guys (and girls)out there! Q:What can a "bad guy"do? A:a lot! o eavesdrop:intercept messages o actively insert messages into connection o impersonation:can fake (spoof)source address in packet (or any field in packet) o hijacking:"take over"ongoing connection by removing sender or receiver,inserting himself in place o denial of service:prevent service from being used by others(e.g.,by overloading resources) more on this later. 8:Network Security 8-7 8: Network Security 8-7 There are bad guys (and girls) out there! Q: What can a “bad guy” do? A: a lot!  eavesdrop: intercept messages  actively insert messages into connection  impersonation: can fake (spoof) source address in packet (or any field in packet)  hijacking: “take over” ongoing connection by removing sender or receiver, inserting himself in place  denial of service: prevent service from being used by others (e.g., by overloading resources) more on this later