This question asks us to evaluate two statements about the IPv4 loopback address, which is a special address used in computer networking.

Let's analyze each statement carefully.

Analyzing IPv4 Loopback Address Statement P: Network Class

Statement P says: The loopback(IP) address is a member of class B network.

To determine if this is true, we need to recall the standard IPv4 address classes and the assigned range for the loopback address.

IPv4 addresses are often categorized into classes (A, B, C, D, E) based on the range of the first octet. The ranges are:

• Class A: 1 to 126
• Class B: 128 to 191
• Class C: 192 to 223
• Class D: 224 to 239 (Multicast)
• Class E: 240 to 254 (Reserved)

The entire network `127.0.0.0/8` is reserved for loopback purposes. The most commonly used loopback address is `127.0.0.1`. Looking at the first octet, which is 127, this falls into the range defined for Class A networks (1 to 126, but 127 is specifically reserved as a block for loopback). Since the first octet is 127, it is part of the network `127.0.0.0/8`. The range `127.0.0.0` through `127.255.255.255` is reserved for loopback.

Based on the standard class definition derived from the first octet, addresses starting with 127 are part of the Class A range, although the entire 127 block is designated for loopback, not general Class A addressing. However, it is definitely not in the Class B range (128 to 191).

Therefore, Statement P, claiming the loopback address is a member of class B network, is False.

Analyzing IPv4 Loopback Address Statement Q: Packet Usage

Statement Q says: The loopback(IP) address is used to send a packet from host to itself.

The primary purpose of the loopback interface (associated with the loopback address like `127.0.0.1`) is for testing and local communication within a single host (computer).

When a program on a host sends a packet to the loopback address (`127.0.0.1`), the packet does not leave the host's network interface card (NIC) and travel onto the physical network. Instead, the operating system's network software stack processes the packet internally and redirects it back to the same host as if it had arrived from an external source.

This functionality allows developers and administrators to test network applications and services without needing an active network connection or another machine. It simulates sending a packet from the host and receiving it back on the same host.

Therefore, Statement Q, stating the loopback address is used to send a packet from host to itself, is True.

Summary of Statement Evaluation

• Statement P: The loopback IP address is a member of class B network. → False
• Statement Q: The loopback IP address is used to send a packet from host to itself. → True

Based on our analysis, Statement P is False and Statement Q is True.

Conclusion on IPv4 Loopback Statements

Comparing our findings with the options, the correct combination is P-False and Q-True.

Revision Table: IPv4 Loopback

Additional Information on IPv4 Loopback

The loopback address block (`127.0.0.0/8`) is formally defined in RFC 1122. While it falls numerically in the space traditionally allocated to Class A networks, it is exclusively reserved for loopback and cannot be assigned to a physical network interface or routed on the public internet.

The loopback interface, often named lo0 or lo, is a virtual network interface. It is always 'up' and reachable as long as the TCP/IP stack is functioning correctly on the host. This makes it ideal for testing local network processes, client-server applications running on the same machine, and checking the health of the network stack itself.

Any data sent to the loopback address is processed by the transport layer (like TCP or UDP) and then passed back up to the application layer on the same host, bypassing the data link and physical layers.