W
William C.
How to check whether eg. certain UDP or TCP ports are closed or open?
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Dusko Savatovic
To display all open ports (TCP and UDP) open cmd prompt and run command:
netstat -ano
To find out which ports are blocked, consult your firewall software. If you
use ICF in WinXP/2003, then only ports that were explicitly opened are
opened, others are blocked. Explicitly opened ports are configured ports
like FTP, Messenger Service, Remote Desktop etc, plus high numbered ports
that are opened when initiating outbound connection. When reply is received
on that port, it is automatically closed and a new one is opened.
If, however, you are not using firewall, then any packet that is received is
forwarded to the corresponding listening service. If listening service does
not exist for that packet (port), the packet is discarded. This may lead to
flooding certain services with malformed packets that may crash the service
and in certain cases can enable attacker to crash service or entire system
or gain complete control of your system.
Dusko Savatovic
netstat -ano
To find out which ports are blocked, consult your firewall software. If you
use ICF in WinXP/2003, then only ports that were explicitly opened are
opened, others are blocked. Explicitly opened ports are configured ports
like FTP, Messenger Service, Remote Desktop etc, plus high numbered ports
that are opened when initiating outbound connection. When reply is received
on that port, it is automatically closed and a new one is opened.
If, however, you are not using firewall, then any packet that is received is
forwarded to the corresponding listening service. If listening service does
not exist for that packet (port), the packet is discarded. This may lead to
flooding certain services with malformed packets that may crash the service
and in certain cases can enable attacker to crash service or entire system
or gain complete control of your system.
Dusko Savatovic
O
Oli Restorick [MVP]
I believe the -o option was introduced in Windows XP, so on Windows 2000
you'd need to omit the "o" from the options.
Oli
you'd need to omit the "o" from the options.
Oli
M
Marc Reynolds [MSFT]
That is correct. Of course you could always use tcpview from
www.sysinternals.com
--
Thanks,
Marc Reynolds
Microsoft Technical Support
This posting is provided "AS IS" with no warranties, and confers no rights.
www.sysinternals.com
--
Thanks,
Marc Reynolds
Microsoft Technical Support
This posting is provided "AS IS" with no warranties, and confers no rights.