Depends upon how you are doing the tarpitting. Back when I did this (15 years ago) I used a program that created a raw socket to handle all TCP traffic that just responded with 0-byte sized windows to all TCP packets (so overhead was minimal). I placed this software on a dedicated server (an old box that wasn't being used otherwise) and routed all our unused IP space to this system. It could keep thousands of connections "live" with minimal resources.
