hey,
can you elaborate a bit more on "encountered a problem that users were having trouble accessing the Internet" .
(also would help stating the HW model and set-up [like cluster and such])
I want to see what problems you encounter as we also have some HUGE load situations randomly (search for my other post) and in our case (and others from here got the same) it seems to be a sort of DNS attack. Still is manageable from our side and we're working to get a final protection/solution implemented.
So, if there is no HW issue (CPU, memory others) then it can be high number of connections.
You can see that in below screenshot from SmartView Monitor...
Ty,