Re: nmap udp scan time

Kevin,
    I believe UDP scans can take such a long time because UNLIKE TCP scans UDP 
does not rely on a handshake and therefore their is no STATE assigned to a 
connection.  If your scanning a firewalled machine that is not replying to the 
UDP packets that are sent to CLOSED ports then I believe your scan will take 
quite sometime to complete. With TCP you will be sending out a SYN packet that 
will only wait a short time frame before determining that that port is either 
Open, Closed, or Filtered.  UDP is a less reliable scan which I believe is 
based on correlating results. It is hard for a UDP scan to determine if a port 
is Open|Filtered unless it discovers a true Closed port. So your scanner may be 
sitting around waiting for responses from ports that will never respond. Next 
time you scan try using a protocol analyzer like Wireshark/Ethereal to see if 
you are getting responses from the majority of ports you have scanned.  This is 
just my understanding of differences in scan types an
 d I apologize if any of my statements are incorrect.


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