Re: How to tell if a given TCP/IP port is open or closed?

From: Karl Levinson [x y] mvp (levinson_k_at_despammed.com)
Date: 08/22/03 

Date: Fri, 22 Aug 2003 14:08:48 -0400

... although note that you'll also see ports that are not listening on your
computer, like your IE browser going out the internet... also, you won't see
ports that are let through on your firewall, which may not be listening on
your computer right now, but might be used later by a worm or trojan. For
example, TCP 25 or 6667 probably isn't open per Netstat, but could still be
a hole that a worm could use to email worms or your passwords out to others,
or remotely control your computer using IRC.

http://securityadmin.info/faq.htm#closeports

The answer sort of depends on what you mean by open. Open port can mean a
service is listening, or it can mean that no service is listening but you
have no firewall or your firewall is not blocking future use of that port.

"Vanguard" <rztqf6v02-NIX@sneakemail-NIX.com> wrote in message
news:OXtQ47MaDHA.2588@TK2MSFTNGP09.phx.gbl...
> "Robert" <nospam@nospam.com> wrote in message
> news:egiH1zMaDHA.3444@tk2msftngp13.phx.gbl
> > How can I determine whether any given port is open or closed?
> >
> > Many thanks, Robert
>
> netstat -a [-n]
>
> Use the -n switch if you want to see all ports as numbers instead of
> friendly/common names, like pop3 and microsoft-ds.
>
>
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