1. Port Scanner:
   1. An application designed to probe a server or host for open ports.
   2. Used by administrators, to verify security policies of their networks, and by attackers, to identify network services running on a host they wish to exploit.
2. Enumeration:
   1. A complete listing of items.
   2. Extract information, including:
      1. Network Shares
      2. Services Running
      3. Groups of Users
3. Network Scanner Operation:
   1. Port Scan:
      1. A process that sends client requests to a range of server port addresses on a host, with the goal of finding an active port on a remote machine. While port scans are not malicious in an of themselves, system administrators would be wise to block inbound ICMP echo request packets anyway.
   2. Port Sweep:
      1. To scan multiple hosts for a specific listening port.
4. Examples:
   1. nmap
      1. A free and open-source security scanner used to discover hosts and services on a computer network, thus building a "map" of the network.
      2. To accomplish its goal, Nmap sends specially crafted packets to the target host(s) and then analyzes the responses.
      3. nmap Cheat Sheet:
         1. https://blogs.sans.org/pen-testing/files/2013/10/NmapCheatSheetv1.1.pdf
   2. netcat
      1. A computer networking utility for reading from and writing to network connections using TCP or UDP.
      2. Netcat is designed to be a dependable back-end that can be used directly or easily driven by other programs and scripts.
      3. At the same time, it is a feature-rich network debugging and investigation tool, since it can produce almost any kind of connection its user could need and has a number of built-in capabilities.
      4. Its list of features includes port scanning, transferring files, and port listening, and it can be used as a backdoor.
      5. netcat Cheat Sheet:
         1. https://www.sans.org/security-resources/sec560/netcat_cheat_sheet_v1.pdf