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Nmap: Techniques for improving scan times

August 16th, 2006 · No Comments


Your objectives for running an Nmap scan will determine how you want it to run: slow and quietly, networksecurity.jpgfast and furious, or somewhere in between. Therefore, Nmap includes a variety of timing options that allow you to affect almost every aspect of a scan.

By default, Nmap is set to not abort a scan due to time — no matter how long it may take to complete. This can be overridden with the Host Timeout option (–host_timeout), which sets the amount of time a scan will wait before giving up on an IP address. This can be useful when scanning network devices over a slow connection or when the scan comes across a device that is slow in responding.

Nmap’s other timing options can basically be split into four categories: round trip time, delay, parallel host scanning and parallel port scanning. Round trip time is the number of milliseconds required to receive a response to an Nmap request. Nmap automatically adjusts its response time timeout during a scan. However, you can force it to use a larger timeout value using the Minimum Round Trip Time Timeout option (–min_rtt_timeout) if, for example, your network is experiencing dropped packets. The Maximum Round Trip Time Timeout (–max_rtt_timeout) is useful for ensuring an accurate scan across slow or problematic networks. Nmap: Techniques for improving scan times

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