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Nmap features include: Fast scan (nmap -F [target]) – Performing a basic port scan for fast result. Host discovery – Identifying hosts on a network. For example, listing the hosts that respond to TCP and/or ICMP requests or have a particular port open. Port scanning – Enumerating the open ports on target hosts.
Port scanning, and nmap, may help to identify which ports are open on suspect IPs, however, even when it says that proxy ports are open the default scan does not check to see if it is an open proxy using that port. It could be a closed proxy expecting authentication, or even a normal website.
The port numbers in the range from 0 to 1023 (0 to 2 10 − 1) are the well-known ports or system ports. [3] They are used by system processes that provide widely used types of network services. On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the ...
Network enumeration is the discovery of hosts or devices on a network. Network enumeration tends to use overt discovery protocols such as ICMP and SNMP to gather information. It may also scan various ports on remote hosts for looking for well known services in an attempt to further identify the function of a remote host.
Most UDP port scanners use this scanning method, and use the absence of a response to infer that a port is open. However, if a port is blocked by a firewall, this method will falsely report that the port is open. If the port unreachable message is blocked, all ports will appear open. This method is also affected by ICMP rate limiting. [4]
Banner grabbing is a technique used to gain information about a computer system on a network and the services running on its open ports. Administrators can use this to take inventory of the systems and services on their network.
Performing a port scan and OS identification (-O option in nmap) on the zombie candidate network rather than just a ping scan helps in selecting a good zombie. As long as verbose mode (-v) is enabled, OS detection will usually determine the IP ID sequence generation method and print a line such as “IP ID Sequence Generation: Incremental”.
On the other hand, a network attacker may use a special type of service scanner, known as a vulnerability scanner, to find devices that have not been patched to find a known vulnerability. [8] An attacker may also use a service scanner to find open administrative ports such as Telnet on TCP/21 and SSH on TCP/22. Once an attacker finds those ...