If you want to quickly check the number of the active connections on your server you can run this command:

netstat -anp | grep :80 | grep ESTABLISHED | wc -l

Don’t forget the semi-colon.
This will work also for all other ports for example SSH on the default 22, or HTTPS on 443.

And this one will list the number of the active connections per IP sorted

netstat -ntu | grep :80 | grep -v LISTEN | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -rn