W3SVC Restart when changing ASP.NET version in ASP.NET tab (IIS)

I'm not sure what is happening but i suspect that i change the ASP.NET version in IIS cause W3SVC restart. All application in the same application pool working ok and restart successfully but other application pull have some issue.

If anyone face the same or similar issue, maybe can share your solution.

Ping an IP through a specific port in cmd prompt or telnet

Well, sometimes we need to know whether the port in open or block, we need to do some checking or troubleshoot through ping/telnet. We cannot ping a IP with port but we can telnet certain IP together with Port no.

For example:
Go to open command prompt, if we want to check whether port 21 is working for IP 203.166.87.9 what we need to do is
> telnet 203.166.87.9 21

please tell me it's work. thanks