CREST Practitioner Security Analyst (CPSA) Practice

How is a Class D address identified in the first bit of its binary structure?

1. It's a "0"

2. It's a "01"

3. It's a "10"

4. It's a "11"

The correct answer is: It's a "11"

A Class D address is identified specifically by having the first four bits set to "1110" in its binary representation. This means that the first bit is always "1", followed by another "1", followed by another "1", and the fourth bit is a "0". Thus, in the context of the entire four-bit prefix "1110", the critical aspect of identifying a Class D address is that it starts with binary digits that indicate multicast communication, which is what Class D addresses are used for. The reasoning behind identifying a Class D address this way relates to how IP addresses are categorized into different classes based on their first few bits. Class D is reserved for multidestination addressing, which is typically used for multicast groups. The patterns in binary help routers and devices determine how to handle the packets destined for those addresses. Understanding the binary structure of IP addresses is essential for networking professionals, as it provides insight into how network communication flows are designed and facilitates the appropriate routing and management of data packets.