I was using nmap to scan the mac addresses of my network.What I found was internet connections and rest of network services badly clogged the users were not able to connect to internet.After messing with different things some times later we noticed on one of machines I was running nmap and stopping it did the trick.
nmap -sP 192.168.1.0/20
Is what I was trying and it basically clogged the entire network. Can some one suggest what can be a remedy for same and why it actually happened?
EDIT
As some people suggested below it generates a lot of ARP traffic
1) is there a way I can measure this ARP traffic?
2) In this case since user applications could not reach internet is there some way I can detect congestion in network.Here nmap was run by me as root so I knew but for future I want to know.