What is Nmap?
Nmap is free tool of network and vulnerability scanning.Network administrators use Nmap to discover how many and which device is connecting in network. It is also use for port scanning.
Though Nmap has evolved over the years and is extremely flexible, at heart it's a port-scan tool, gathering information by sending raw packets to system ports. It listens for responses and determines whether ports are open, closed or filtered in some way by, for example, a firewall. Other terms used for port scanning include port discovery or enumeration.
How it's works?
Basically,Nmap is a port-scan tool, gathering information by sending raw packets to system ports. It listens for responses and determines whether ports are open, closed or filtered in some way by, for example, a firewall. Other terms used for port scanning include port discovery or enumeration.
Port Scanning
Nmap is also use for port scanning.The packets that Nmap sends out return with IP addresses and a wealth of other data, allowing you to identify all sorts of network attributes, giving you a profile or map of the network and allowing you to create a hardware and software inventory.
How to use Nmap?
One of the beauties of Nmap is that beginners with little system or network knowledge can get started with simple commands for basic scanning, while professionals can take advantage of more complex sorts of probes, which result in more fine-grained view of a network.
What you get when you use Nmap is essentially a list of the targets you've scanned, along with information associated with those targets. The information you receive depends on the sort of scan you do – in other words, the commands you've used.
Depending on the command, scans don't necessarily generate a lot of traffic and don't have to be very intrusive. Scanning all ports on all systems would be inefficient, primarily since only a fraction of available ports are going to be in use at any one time (a system can have 65,535 TCP ports and 65,535 UDP ports). Different options allow for finetuning or expanding scans. In service version detection for example, available options include:
sV (enables version detection)
version-intensity (sets scan intensity)
Intensity ranges between 0 and 9, and establishes the sort of probes that you want to apply. A lower-number intensity scan will probe for common services, while a higher-number intensity scan can identify lesser-used services correctly but takes longer.
Different commands can also, for example, let you specify which ports or subnets to scan or skip.
Nmap includes a scripting engine using the Lua programming language to write, save and share scripts that automate different sorts of scans. Though they are frequently used to check for well-known network infrastructure vulnerabilities, all sorts of tasks can be automated.
Zenmap, The Nmap GUI
Zenmap is the Nmap security scanner graphical user interface and provides for hundreds of options. It lets users do things like save scans and compare them, view network topology maps, view displays of ports running on a host or all hosts on a network, and store scans in a searchable database.
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