🚀 go-pugleaf

1) You "Open" a port by installing software that uses that port.
2) You "close" a port by uninstalling software that uses the port.
3) You "block" a port by opening it ( see #1) and putting a firewall in 
front of it.



> 1a. Does a service or program have to be listening on a port to test
> if its open, or is there a way for example I could open a port on a
> software based firewall, and test if its open without anything
> listening on that port?

See # 1. Opening a port on the firewall is different from opening a port on 
a computer.

> 2a. It appears to me that netstat -an only show ports that are (a)
> open and (b) have a program/service listening or using it?

See #1.

Hypothetically, if a port is open and no one is listening to accept the 
communication on the other end, is the port *really* open?


hth
DDS
"Al" <bigal.nz@gmail.com> wrote in message 
news:fe3c624c-27ad-4526-a137-3b6a435fea47@v37g2000prg.googlegroups.com...
> Hi All,
>
> I want to clarify a few misconceptions I (think) I have about ports,
> and specifically testing whether or not they are open.
>
> 1. Whats the best way to test if a port is open on a computer. I dont
> nessecarily mean testing if its open to the internet, but just on the
> computer - this rules out online port scanners since many PC's will be
> behind a router, and I am not testing that, but more software based
> firewalls that may be running.
>
> 1a. Does a service or program have to be listening on a port to test
> if its open, or is there a way for example I could open a port on a
> software based firewall, and test if its open without anything
> listening on that port?
>
> 2. With netstat -an what do the *.* mean?
>
> 2a. It appears to me that netstat -an only show ports that are (a)
> open and (b) have a program/service listening or using it?
>
> 3. Whats the best software to do this?
>
> Any positive replies appreciated.
>
> -Al 

 Al <bigal.nz@gmail.com> wrote:

>1a. Does a service or program have to be listening on a port to test
>if its open, or is there a way for example I could open a port on a
>software based firewall, and test if its open without anything
>listening on that port?

www.GRC.COM has ShieldsUP!. This statement usually starts an argument,
but it will show if you have any open ports.
-- 

Because you always wanted to know what happens when you hit a piano key.
http://www.concertpitchpiano.com/grandactionanimated.gif

"Al" <bigal.nz@gmail.com> wrote in message 
news:fe3c624c-27ad-4526-a137-3b6a435fea47@v37g2000prg.googlegroups.com...
> Hi All,
>
> I want to clarify a few misconceptions I (think) I have about ports,
> and specifically testing whether or not they are open.

Danny has given an excellent overview, which covers most points.

> 1. Whats the best way to test if a port is open on a computer. I dont
> nessecarily mean testing if its open to the internet, but just on the
> computer - this rules out online port scanners since many PC's will be
> behind a router, and I am not testing that, but more software based
> firewalls that may be running.

A simple way is to use telnet.

Open a new command prompt window and enter:
    telnet computerName port
using the name of the computer and port that you wish to test.

If it simply says "Connecting To computerName..." and eventually times out 
then there is either nothing listening on that port or its blocked. ANY 
other response indicates that something is listening on that port.

Alternatively download cryping (command line utility) and you can use it to 
test a port using:
    cryping computerName -port port
It will indicate whether or not it could successfully connect to the port. 
You can download it here http://www.cryer.co.uk/downloads/cryping/

Hope this helps.
-- 
Brian Cryer
www.cryer.co.uk/brian 

On Fri, 2 Oct 2009 10:05:18 +0100, "Brian Cryer"
<not.here@localhost> wrote:

>"Al" <bigal.nz@gmail.com> wrote in message 
>news:fe3c624c-27ad-4526-a137-3b6a435fea47@v37g2000prg.googlegroups.com...

>> I want to clarify a few misconceptions I (think) I have about ports,
>> and specifically testing whether or not they are open.
>
>Danny has given an excellent overview, which covers most points.
>
>> 1. Whats the best way to test if a port is open on a computer. I dont
>> nessecarily mean testing if its open to the internet, but just on the
>> computer - this rules out online port scanners since many PC's will be
>> behind a router, and I am not testing that, but more software based
>> firewalls that may be running.
>
>A simple way is to use telnet.
>
>Open a new command prompt window and enter:
>    telnet computerName port
>using the name of the computer and port that you wish to test.
>
>If it simply says "Connecting To computerName..." and eventually times out 
>then there is either nothing listening on that port or its blocked. ANY 
>other response indicates that something is listening on that port.

True. But alternatively, getting nothing in return with telnet
does not imply that nothing is listening on that port :-)
(As I recently found out when attempting to ascertain if a SSL
host was listening :-)

>Alternatively download cryping (command line utility) and you can use it to 
>test a port using:
>    cryping computerName -port port
>It will indicate whether or not it could successfully connect to the port. 
>You can download it here http://www.cryer.co.uk/downloads/cryping/

Nice tool ! Correction: very nice tool!
And it gets a respons from SSL :-)

>Hope this helps.

Certainly helped me :-)

-- 
met vriendelijke groet,
Gerard Bok