Query open TCP Ports in DotNet

[Cliff]

I need to get a list of "Open"/In-Use TCP Ports (actually to see if
there is a cponnection with a destination Port of 21)

I think what I'm after is similar to the output of netstat. I could run
netstat and parse the output, but I'd prefer not to as I'm going to be
doing this in a service and it needs to monitor the ports every few
seconds.

Any advice on how I can do it.

What I'm trying to do is control the way an FTP Process works, and
perform an action on the successful connection of an outgoing port
connecting to 21, then perform another action if a data connection is
required (i.e. the incoming port 20 connection)

There is a firewall on the computer this will be running on, I don't
know how a firewall takes the action of blocking a port, would the
firewall actually STOP that port from being created in the first place,
or allow it to be created, but then not used...?

Thanks

Cliff.