Hello,

when i do command "netstat -nt|wc -l" i get around 1200.

i would like to ask if i can use any Linux utility/command to monitor performance impact of the network connections.

Ideally to see CPU/RAM/slowness impact. The server is 16+ threads, 4GB RAM free.
I would like to safely determine how many connection is still good or if i need to decrease.

Im not interested to see server load in general, or the work done as a result of the connection (showing a webpage for example), but just connection itself impact.

Thank You

Write a script that connects a remote machines to the server using the sessions type appropriate. Do nothing on the node other than establish and maintain the inbound sessions, measure overhead on the node as you add each connection.
At some point, you'll see the beginnings of a geometrically escalating curve in your data. If that isn't being driven by a setting on the node (max_ssh_sess) or the software (apache connection_limit) then you'll know, beyond here be dragons.

EDIT:
You can get around this problem on a physical node by bonding adapters (aggregating the available resources to handle additional load). On a virtual machine, you can bond the adapter as well but you also have settings in the adapters xml file that control the resources associated with the adapter (and hence the workload it can handle)