The easiest way to make a scan run faster is to use the built-in timing flags. These flags are invoked using -T and a number from 1 (slowest) to 5 (fastest). The default scanning speed is -T3, right in the middle.

There are a few risks to use significantly faster scanning, since it creates certain unreliable aspects in the scan. Particularly, if your network interface is known to be reliable, these options should be used with caution!

The default timing flags change six different elements—many of which we'll go into specific detail, later in this chapter. Specifically, the timing flags change the individual values of initial_rtt_timeout, min_rtt_timeout, max_rtt_timeout, max_parallelism, scan_delay, and max_scan_delay. Don't worry if these flags sound strange to you—we'll cover the different ones you need to know in enough detail that you should be able to debug a large variety of network and performance issues.

The preceding screenshot, downloaded from http://www.professormesser...