(ISC)2 Certified in Cybersecurity Practice Exam

How many possible ports are there on a network?

1. A) 65,300

2. B) 1,000

3. C) 10,000

4. D) 65,535

The correct answer is: D) 65,535

In the context of networking, the number of possible ports is determined by the TCP/IP protocol suite, which defines the range of ports that applications can use for communication. Ports are 16-bit numbers, allowing for a total of 2^16, or 65,536 different values. However, since the port numbering begins at 0, the available port numbers effectively range from 0 to 65,535, making the total count of possible ports 65,536. This total accounts for a variety of ports, including well-known ports (0 to 1023), registered ports (1024 to 49151), and dynamic or private ports (49152 to 65535). The well-known ports are assigned to specific services and protocols, while registered and dynamic ports provide additional flexibility for various applications. The other options do not capture the full range of ports defined by the protocol suite, making them less accurate. Thus, the correct answer reflects the full extent of possible ports available in a networked environment.