How to Supercharge Your Nmap Scans - Professor Messer IT Certification Training Courses (2024)

FAQs

How to scan 1000 ports in Nmap? ›

The simple command nmap <target> scans 1,000 TCP ports on the host <target> . While many port scanners have traditionally lumped all ports into the open or closed states, Nmap is much more granular. It divides ports into six states: open , closed , filtered , unfiltered , open|filtered , or closed|filtered .

A low --max-scan-delay can speed up Nmap, but it is risky. Setting this value too low can lead to wasteful packet retransmissions and possible missed ports when the target implements strict rate limiting. Another use of --scan-delay is to evade threshold based intrusion detection and prevention systems (IDS/IPS).

Scanning specific port ranges

There are several ways of using the Nmap -p option: Port list separated by commas: $ nmap -p80,443 localhost. Port range denoted with hyphens: $ nmap -p1-100 localhost. Alias for all ports from 1 to 65535: # nmap -p- localhost.

Alternatively, you can specify the -F (fast) option to scan only the 100 most common ports in each protocol or --top-ports to specify an arbitrary number of ports to scan. When none of these canned port sets suit your needs, an arbitrary list of port numbers can be specified on the command-line with the -p option.

Estimate and Plan for Scan Time

So the total time Nmap will spend scanning the network can be roughly extrapolated by multiplying 21 minutes per host by the number of hosts online. If version detection or UDP are being done as well, you'll also have to watch the timing estimates for those.

Masscan can be compared with other tools like Nmap. Due to its focus on high performance, this tool can be used when many systems have to be scanned at once. It can scan all internet hosts on IPv4 within 5 minutes. This impressive statistic makes the tool loved by those that do security research.

SYN scan is the default and most popular scan option for good reasons. It can be performed quickly, scanning thousands of ports per second on a fast network not hampered by restrictive firewalls. It is also relatively unobtrusive and stealthy since it never completes TCP connections.

Network probing or port scanning tools are only permitted when used in conjunction with a residential home network, or if explicitly authorized by the destination host and/or network. Unauthorized port scanning, for any reason, is strictly prohibited.

Do real hackers use Nmap? ›

However, hackers can also use Nmap to access uncontrolled ports on a system. They can run Nmap on a targeted approach, identify vulnerabilities, and exploit them. But Nmap is not only used by hackers - IT security companies also use it to simulate potential attacks that a system may face.

Nmap is the go-to tool for discovering hosts, identifying open ports, and assessing the overall security posture of a network. Wireshark, on the other hand, excels in capturing and analyzing the nitty-gritty details of network communication, making it indispensable for troubleshooting and security investigations.

Nmap builds on previous network auditing tools to provide quick, detailed scans of network traffic. It works by using IP packets to identify the hosts and IPs active on a network and then analyze these packets to provide information on each host and IP, as well as the operating systems they are running.

Nmap scripts are stored in a scripts subdirectory of the Nmap data directory by default (see Chapter 14, Understanding and Customizing Nmap Data Files). For efficiency, scripts are indexed in a database stored in scripts/script.

By default, Nmap scans the most common 1,000 ports for each protocol.

Nmap uses the flag -p for setting the port ranges to be scanned. This flag can be combined with any scanning method. In the previous example, we used the argument -p80 to indicate to Nmap that we are only interested in port 80.

A port scan will be about 10 times as fast if you only scan 100 ports instead of the default 1,000. You can scan just the most popular 100 ports with the -F (fast scan) option, specify an arbitrary number of the most commonly open ports with --top-ports , or provide a custom list of ports to -p .