where do i have to run the ab?
Im trying to see how many concurrent connections can the server handle on stress.
Well then it should be fairly obvious. If you run it on your server, then it is going to impact the performance of your server. You will not get a true answer about how your server performs under load since some of your server resources will be devoted to running the benchmark.
What you may need to do is setup a computer, or possibly several computers to act as clients. If you have good hardware, and things are setup really well, you might not be able to actually stress out a server from a single client machine.