The Port Scan window allows you to scan a range of protocol ports to check for available services (listeners). This is especially useful for testing network security including firewalls by verifying that there are no unintended services available.
Enter the IP Address of the host you wish to scan along with the starting and ending port numbers in the corresponding fields and press Scan to begin scanning. If you have access to a Domain Name Server (DNS), you can type a DNS host name like "www.myhost.com" (or IP address) in the target field and press Return. If you leave the Ending Port empty, only the Starting Port number will be scanned. You can also specify a port range in the target field using the form address:start-end.
You can scan for TCP services, UDP services, or both.
Notice that port scanning can be used both to check the security of your own network, and to probe for weaknesses in remote networks. Some hosts or routers may interpret port scanning as a hostile attack and cut-off subsequent service. The rate of port scanning is adjusted based on the observed round trip time to avoid flooding network buffers.
TCP ports are scanned by trying to open a connection to each port and waiting 2 seconds to see if the connection is accepted or cancelled (Reset) by the remote peer. If the connection request times out after other responses have been received, a red "X" is displayed indicating that the port appears to be operating in "stealth" mode since there was no response.
UDP ports are scanned by sending a UDP datagram to each port and checking for an ICMP destination unreachable response. Since detecting a UDP listener depends on not seeing an ICMP response from the target host, spurious ports may appear if the path to the remote host is unreliable. You can use the status headings in the lower left corner of the window to verify how many responses have been received.
When you invoke one window from another, the corresponding data is automatically transferred.
You can select the results of a Port Scan and copy them to the clipboard as plain text (for pasting into email messages). If you include the first row of the table in your selection, the table headings will also be copied.
You can open and use multiple Port Scan windows at the same time.
A popup menu keeps a list of Recent Targets or history. The contents of the target field are added to the list when a test to that target is invoked. If the recent targets menu becomes full (10 entries), the least recently used item will be removed. To add or remove an item, or clear the entire list, use the corresponding selections from the History menu.