Port scanning may be defined as a surveillance technique, which is used in order to locate the open ports available on a particular host. Network administrator, penetration tester or a hacker can use this technique. We can configure the port scanner according to our requirements to get maximum information from the target system.
Now, consider the information we can get after running the port scan −
Information about open ports.
Information about the services running on each port.
Information about OS and MAC address of the target host.
Port scanning is just like a thief who wants to enter into a house by checking every door and window to see which ones are open. As discussed earlier, TCP/IP protocol suite, use for communication over internet, is made up of two protocols namely TCP and UDP. Both of the protocols have 0 to 65535 ports. As it always advisable to close unnecessary ports of our system hence essentially, there are more than 65000 doors (ports) to lock. These 65535 ports can be divided into the following three ranges −
System or well-known ports: from 0 to 1023
User or registered ports: from 1024 to 49151
Dynamic or private ports: all > 49151