RE: verifying an open or closed port on an ip address

["Jason Coombs" <jasonc () science org>]

you can't determine conclusively whether a port is 'open' from a remote
location. what actions does your CPU take when bits arrive on an exposed
network interface? If you don't know, then you can't tell whether a port is
open. judging a port to be 'open' because it responds to the TCP 3-way
handshake and 'closed' otherwise is wrong, even if you only care about TCP and
ignore UDP.

-----Original Message-----
From: ian () kingcon com [mailto:ian () kingcon com]
Sent: Thursday, August 07, 2003 7:45 AM
To: security-basics () securityfocus com
Subject: verifying an open or closed port on an ip address


Hello,

I am looking for a windows compatible utility or method, preferably command
line, where I can verify whether a port on an ip address is reachable or not.
I want to be able to do individual ports and not port scans.  Say for instance
I wish to verify that port 677 is closed to traffic on ip address Ex.
172.16.0.1, I'm looking for a utility that would do something like:

Check 172.16.0.1 port 677

and tell me whether that port was reachable.

So if I have two networks and I use this command from one I can determine
whether a port is reachable on another.  To determine whether a security
measure is failing or not.

There may be a simple way to do this...

Thanks
Ian
:)



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