I want to stress my .net web service, It feels like something is limiting the concurrent connections I can have.. even when trying from 2 different computers on them server the results were pretty the same. (All of this is done locally, server and clients are on local network so response time is very fast)
So is there a settings I need to change in my server machine to allow more incoming connections?
There are various things that can limit the amount of processing possible, each of which require research to see if they apply. So you might want to add more to your question about what has been verified today.
Regardless, based on your information I would assume that SessionState is enabled. This, with default behavior will limit processing to a single request at a time for each client due to synchronization locks for guaranteed read-write ability. I assume this is the root cause of what you are seeing today. This StackOverflow post talks about this specifically
Others have posted various details in the comments that can help also.
I have found though that load testing is best done from outside sources as well to ensure your entire production pipeline is involved. (Network components, etc)